Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session G60: Poster Session IPoster Undergraduate
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Room: LACC West Hall A |
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G60.00001: UNDERGRADUATE RESEARCH
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G60.00002: Visualizing Fluid Physics of Microswimmers Sara Al Bassri, Wylie Ahmed Microscopic swimming organisms must generate forces that result in fluid flows to facilitate their motion and feeding. Studying the flow physics of swimming microorganisms is important to have a better understanding of their thermodynamics and interactions with their environment. Therefore, we developed an analysis based on the visualization of fluid flow using the flowtrace algorithm in ImageJ/Fiji. This allows us to quantify universal fluid flow patterns generated by a variety of organisms. So far, we observed that organisms generate vortices via cilial beating. The average velocity of the vortex exhibited a characteristic decay with distance from the cilia. Additionally, in organisms that vary in size by nearly 10 times, we found that the ratio of vortex size to cilia length is conserved, with a value of 5.00 ±0.86 (mean ±SD). This observation suggests the underlying flow physics may follow a scaling behavior for organisms of different sizes as they generate vortices for feeding. |
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G60.00003: Fly Swarms and Complexity Bebee Austin, Troy Taylor, Joelle Murray A system is considered complex if it is composed of individual parts that abide by their own set of rules while the system, as a whole, exhibits unexpected properties. The motivation for studying complexity spurs from the fact that it is a fundamental aspect of many systems, including forest fires, earthquakes, stock markets, fish schools, plant root growth, and fly swarms. We are particularly interested in fly swarms and the possible complex properties that swarms exhibit, arising from individual fly interactions. |
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G60.00004: Illustrating the differences between a Superposition and a Mixture of States Muhammad Aziz, Allan Delarosa, Sean Bentley This experiment is a quantum eraser experiment that makes use of a path type entanglement. Since pairs of photons are generated, the goal is to generate a double-slit interference pattern from one half of a momentum entangled photon ensemble by performing a local transformation on the other, and subsequently detecting the entangled pairs. A classical system was also prepared to mimic the quantum entangled system where we did not have entangled photons and the two paths were attenuated to a single photon level. It was found that in a mixture, unlike a superposition, there is no way to erase the which-slit information and generate a double-slit interference pattern. |
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G60.00005: Nonequilibrium Dynamics of Active Colloids Paris Blaisdell-Pijuan, Mauricio Gomez, Ngoc La, Wylie Ahmed Self-propelled colloids are an example of an active matter system that can be precisely controlled to investigate their nonequilibrium behavior. Under blue-light illumination, the asymmetric colloids generate phoretic and osmotic driving forces that cause self-propulsion and deviate their dynamics from non-active equilibrium particles. Here, we present the thermal and non-thermal diffusion of the colloids using video microscopy, image analysis, and approaches from statistical mechanics. Using a mean-squared displacement (MSD) analysis we characterize the motion of these colloids as directed and non-directed. The velocity autocorrelation function (VACF) was also studied to investigate directional persistence. The diffusion coefficient of these colloids was calculated using both methods (MSD and VACF), and compared to particles in equilibrium. Active and thermal diffusion has been characterized, helping to indicatie transitions between random and directed motion. We have examined the efficiency of the active colloids by comparing the energy provided and dissipated in the system. This study helps set the foundation for understanding the fundamental physics of active matter and complex diffusive systems. |
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G60.00006: Charge Current Quasi-Elastic Neutral Hyperon Production in ArgoNeuT Samuel Borer
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G60.00007: Investigation of the system La2-xSrxNiO4+δ via measurements of thermodynamic and transport properties Jefferson Carter, Benjamin White Stripe order in cuprates and nickelates has been the subject of intense research activity over the last few decades. The potential connection between stripe order and high-temperature superconductivity makes elucidating the underlying mechanism that drives stripe order an important problem. Stripe order has been observed in the system La2-xSrxNiO4+δ for 0.25 ≤ x ≤ 0.8. Chemical substitution of Sr2+ for La3+ dopes holes into the NiO2 planes and induces a variation of the Ni2+/Ni3+ ratio. In the stripe-ordered state, homogeneous striped regions of Ni3+ ions bisect regions of antiferromagnetic order associated with magnetic moments on the Ni2+ ion sites. To investigate the system |
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G60.00008: jlj;kl Michelle Chen, Alex koch jkj;k |
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G60.00009: Mixing Analysis of Serpentine Microfluidic Mixers with Non-Rectangular Cross-Section Joshua Clark, Petru Fodor Serpentine or spiral shaped channels have been used in the past as a way to induce mixing in microfluidic type devices. In this approach one exploits the cross-sectional flows, also known as Dean flows, resulting from the centripetal forces experienced by the fluid as it is forced to move around a curved trajectory. However, it has to be noted that the quality of mixing is strongly dependent on the Reynolds number, with good results being achieved only at high flow rates. In this work we exploit the use of channels with asymmetric non-rectangular sections to improve the mixing quality in this type of microchannels. Alternating the orientation of the non-rectangular cross-section between the serpentine channel segments generates more complex fluid flows with a positive impact on the performance of the mixers. The fluid flows characteristics are determined numerically from computational solutions to the Navier-Stokes equations and the concentration - diffusion equation. We found that the performance of these mixers exceeds that of unmodified channels and we currently assess their performance relative to other state of the art methodologies. |
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G60.00010: PIXE Analysis on Artificial Turf Skye Conlan, Michael Vineyard, Scott LaBrake, Sajju Chalise, Zachary Porat In recent years, there has been debate regarding the use of the crumb rubber infill in artificial turf on high school and college campuses due to the potential presence of heavy metals and carcinogenic chemicals. We performed Proton-Induced X-Ray Emission (PIXE) analysis of artificial turf infill and blade samples collected from high school and college campuses around the Capital District of NYS to search for potentially toxic substances. Crumb rubber pellets were made by mixing 1g of rubber infill and 1g of epoxy. The pellets and the turf blades were bombarded with 2.2 MeV proton beams from a 1.1-MV tandem Pelletron accelerator in the Union College Ion-Beam Analysis Laboratory and x-ray energy spectra were collected with an Amptek silicon drift detector. We analyzed the spectra using GUPIX software to determine the elemental concentrations of the samples. The turf infill showed significant levels of Ti, Fe, Co, Ni, Cu, Zn, Br, and Pb. The highest concentration of Br in the crumb rubber was 1500 +/- 100 ppm while the highest detectable amount of Pb concentration was 110 +/- 20 ppm. The artificial turf blades showed significant levels of Ti, Fe, and Zn with only the yellow blade showing concentrations of V and Bi. |
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G60.00011: High-Resolution Interference Patterns using Nonlinear Absorption Allan Delarosa, Sean Bentley, Muhammad Aziz We use thin films of CdSe nanoparticles as a multi-photon absorber in order to write interference patterns with two to three times the resolution that would normally be allowed by the diffraction limit for linear techniques. Using a patented phase-mask, nonlinear interference method developed in our lab, we will demonstrate the generation of arbitrary patterns with the higher resolution. |
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G60.00012: Speed of Cosmic Ray Muon Using Silicon Photomultipliers Jose Diaz, Jefferson Quiambao Recently, the silicon photomultiplier (SiPM) has attracted considerable attention as a possible replacement for the conventional photomultiplier detector (PMT). To realize the practicality of the SiPM detectors, we developed a 4-fold coincidence experiment to measure the speed of the cosmic ray muons. Moreover, cosmic rays are highly energetic atomic nuclei mainly originating outside the Solar System. After striking the Earth’s atmosphere, cosmic rays are broken into different particles, one of which is the muon. Furthermore, our experimental apparatus consisted of a coincidence setup, a digitizer, and two pairs of cosmic ray detectors involving SiPMs and PMTs. The distance between the two pairs of detectors was periodically altered to determine the arrival time difference between them in order to accumulate time histograms with 3000 coincidence events. Detailed data analysis was conducted using the CERN software package Physics Analysis Workstation (PAW) in a Linux-based operating system. Utilizing the data for the distance and time difference, we were able to measure the speed of the cosmic ray muons. |
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G60.00013: Chemical Vapor Deposition of Two-Dimensional Heterostructures Tania Diaz Marquez, Prasana Sahoo, Humberto Gutierrez Two dimensional (2D) materials such as transition metal dichalcogenides (TMDs) are being studied for their potential applications in opto-electronics, given their distinct structural and electro-optical properties. Laterally stacked TMD heterostructures are crucial components for constructing p-n junctions, light-emitting diodes, photovoltaic devices, and tunneling transistors. A large scale and controlled growth of these lateral heterostructures is necessary to exploit the TMDs potential for applications in flexible nanoelectronics.The objective of this research was to optimize the growth of laterally connected semiconducting MoSe2-WSe2 and MoS2-WS2 bilayer heterostructures, using the Chemical Vapor Deposition (CVD) technique.This synthesis method is relatively simple, and allows the fabrication of single and multiple junction heterostructures with the change of the carrier gas supplied during growth.Through Raman and Photoluminescence characterization, the heterostructure samples were examined to confirm chemical composition, structural homogeneity, and distinguishable interfaces of the TMDs heterojunctions. The optimal conditions for the bilayer growth of MoSe2-WSe2 and MoS2-WS2 heterostructures were established and the growth was repeated to corroborate effective replication. |
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G60.00014: Pristine Mica: cleaving under organic solvents and variable temperature Au sputter deposition Brian Evans, Indrajith Senevirathne, Tyler Adams, Chadd Miller Mica is a versatile material that can be cleaved to form pristine layers allowing it to be an excellent substrate for mico/nanotechnological processes. Such as a smoother starting substrate for a film provides a more consistent film. Blade cleaving under the ambient conditions exposes the process to unique set of conditions. To vary such conditions mica was Blade cleaved submerged under different organic solvents. The varying surfaces resulted will be discussed in terms of the surface roughness and consistency. Surfaces were imaged via Atomic Force Microscope (AFM) using intermittent contact mode. Surfaces with varying roughness and consistency obtained and where analyzed and compared. Subsequently Au was deposited via magnetron sputtering. Sputter deposition was carried out at different substrate temperatures to facilitate/inhibit surface diffusion and agglomeration kinetics of the nanoclusters on the surface. The resulting varying surfaces were imaged via intermittent contact AFM. The results will be discussed with respect to the varying deposition temperatures. Many surfaces were shown to be of Stranski – Krastanov (SK) type growth. |
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G60.00015: Computational and Analytical Modeling for Senate Decision Dynamics Rossella Gabriele, Rebecca Melkerson, Margaret Kallus, Irina Mazilu For decades, congressional scholars have struggled to measure and describe the impact of influences on Senate decisions. While quantitative data on these political issues is scarce, this study introduces an interdisciplinary stochastic model to determine Senate decision outcomes based on assumptions about influence. We consider both interactions between Senators and the effect of external lobbying. The model is based on the classic Ising Model, and the system is defined as a 1D lattice with 100 sites, where the sites hold values for the senators’ political convictions. Peer influence is analogous to the spin-to-spin coupling constant in the Ising model, and the effect of professional lobbying replaces the interaction of the spins with an external magnetic field. Lobbying influence approximates the effects of social media campaigns, face-to-face meetings with Senators, and financial contributions. Peer-to-peer influence is modeled by using each Senator’s partisan score, such that the influence is a function of the numerical difference between these scores. We analyze the model using Python and matrix algebra. Given a specific political issue, the model predicts the outcome of the senate vote. |
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G60.00016: Zinc Tungstate Scintillators for Low Energy Electron Microscopy Derek Grove Zinc tungstate is a crystalline material that emits light as result of electron bombardment. We have deposited ZnWO4 films with electrical conductivity enough to prevent charging, photoluminescence quantum efficiency of 23%, which are mechanically durable. This makes it a viable thin film coating for scintillators inside an SEM with the added benefit that it can deliver signal even at low energy of the electrons. Our theory is that zinc tungstate as a thin film on top of scintillators offers more benefits for low energy back scattered electron microscopy than ITO or Al, two materials that do not emit light in the presence of electron radiation. We have taken images at low accelerating voltages with two types scintillators, YAP with a thin film of zinc tungstate on top and YAG with ITO. The comparison shows much higher signal to noise ratio for the scintillator with zinc tungstate, and imaging with it at electron energies, where no image can be collected with the scintillator with ITO. The ability of the zinc tungstate film to prevent charging was confirmed with measurement of the electron emission vs. accelerating voltage. These curves are however, very sensitive to the surface properties of the sample. |
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G60.00017: Magnetotelluric Investigations of the Yellowstone Caldera: Understanding the Emplacement of Crustal Magma Bodies Rebeca Gurrola, Bryce Neal, Adam Schultz, Ninfa Bennington, Brady Fry, Laney Hart, Esteban Bowles-Martinez, Naoto Imamura, David Miller, Reagan Cronin, Kathryn Scholz, Anna Kelbert, Rolando Carbonari Wideband magnetotellurics (MT) presents an ideal method for imaging conductive shallow magma bodies associated with contemporary Yellowstone-Snake River Plain (YSRP) magmatism. Particularly, how do these magma bodies accumulate in the mid to upper crust underlying the Yellowstone Caldera, and furthermore, what role do hydrothermal fluids play in their ascent? During the summer 2017 field season, two field teams from Oregon State University and the University of Wisconsin-Madison installed forty-four wideband MT stations within and around the caldera, and using data slated for joint 3-D inversion with existing seismic data, two 2-D vertical conductivity sections of the crust and upper mantle were constructed. These models, in turn, provide preliminary insight into the emplacement of crustal magma bodies and hydrothermal processes in the YSRP region. |
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G60.00018: Diagnostic Evaluation of NuMI Hadron Monitor Ion Chambers Bernadette Haig, Katsuya Yonehara The performance of the NuMI Hadron Monitor ion chambers was evaluated. Possible sources of ion chamber performance degradation are discussed, based upon analysis of Monitor data. The quality of the signal is reviewed, and it is concluded that the Monitor still functions for its main tasks. Repair is not possible, but replacement of the Hadron Monitor during the 2017 summer shutdown was not deemed necessary. Lastly, a diagnostic apparatus for potential impurity of the helium gas inside the chamber has been designed and installed. A vacuum chamber is connected to the Hadron Monitor exhaust line to collect gas samples. These samples are analyzed by a GCMS (gas chromatograph-mass spectrometer). |
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G60.00019: Synthesis and Computational Analysis of Novel IspF Inhibitors Daniel Harper, Matthieu Rouffet, Lane Votapka We present a mixed chemical, biological, and physical approach to the identification of novel inhibitors of 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase (IspF). This enzyme is involved in the synthesis of an essential class of biomolecule in pathogens, isoprenoids. Therefore, a potent inhibitor of this enzyme has potential to produce a new class of antibiotics. A selection of potential inhibitors was generated using chemical methods and tested for activity against IspF using biological methods. These results were used to inform and verify the validity of a computational approach for identification of further inhibitors. This computational approach used Newtonian mechanics, the AMBER force field, and free energy perturbation to predict the relative inhibition of potential inhibitors. |
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G60.00020: Studying the Volume Phase Transition of Polymeric Microgels Samantha Hudson, Samantha Tietjen, Kiril Streletzky This project investigated volume phase transition of polysaccharide microgels synthesized in a surfactant solution. The addition of surfactant raises the Lower Critical Solution Temperature (LCST) of the polymer. Maintaining LCST for 3 hours is crucial for microgel synthesis. Three baths were used to achieve these stable synthesis conditions. While most microgels were synthesized in +/-0.1C bath, microgels synthesized in a less stable baths were found to have larger hydrodynamic radii (Rh). The synthesis conditions were varied systematically by changing amount of used cross-linker and surfactant. The resulting microgels were characterized using Dynamic Light Scattering (DLS) at multiple angles and temperatures varying from 20 to 60C. Flory-Huggins Mean Field theory was used to describe microgel’s deswelling with increase of temperature. The theoretical model was fit to the experimental DLS data. Fit results, including enthalpy, entropy, number of polymer chains per microgel, and a material constant, suggest a dependence of polymer chain interactions during synthesis on the amount of cross-linker. Further development of the Flory-Huggins model is needed to fully account for effect of cross-linker and surfactant on synthesized microgels. |
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G60.00021: A New Paramagnetic and Piezoelectric Organometalic Material Alessa Ibrahim, Gabriel Lopez, John Montano We have synthesized a new organometallic material that is predicted to be multiferroic. Ferroelectric materials can pave a way to exciting new technologies, such as FRAM. Bis(Diisopropylamonium) Cobalt(II) Tetrachloride, BLUE, is grown from beaker solutions containing; molar solution Cobalt(II) Chloride Hexahydrate(237.93g/L), Hydrochloric Acid (HCL), and Diisopropylamine (DIPA). Crystals can form in small needle like morphology within one week, larger crystals can take two or more months. Its density is 1.309 g/cm3 and melting point is above 130°C. Dipole strength along each axis (a, b, c) respectively are -7.8541, 99.567, and -56.677 e-Å. The dipole strengths indicates the polar axis along a diagonal, predicted from theory to be 28° off the b-axis. Atomic Force Microscopy testing has shown ferroelectric and piezoelectric results. The Radiant System testing has shown butterfly curves that indicate piezoelectric responses for different samples of blue when tested with an electric field that ranges between 5-15 Kv/cm. However, at the electric field of 11-15 Kv/cm the break down voltage of blue crystals is noted. Further testing is to be conducted on larger crystals and different axes with Atomic Force Microscopy and bulk capacitance testing. |
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G60.00022: Optical Tweezers for Force Measurement in Living Cells Corbyn Jones, Wylie Ahmed Optical tweezers are used to manipulate microscopic objects and measure forces and displacements at the piconewton and nanometer scale. This is accomplished by tightly focusing a laser, which is capable of locally trapping objects. Measurements are often done with beads in simple viscous liquids, where calibration is relatively simple. However, in order to analyze the inner components of living cells (embedded in cytoplasm) with unknown optical and physical properties, new calibration methods for the optical tweezers must be used. Two methods of force calibration for intracellular measurements are the Photon Momentum Method and the Active-Passive Method. We are developing a system capable of using both calibration methods. This will enable us to precisely measure the force kinetics in the cytoplasm of living cells and quantify their mechanical activity. We are investigating the relationship between thermal and non-thermal fluctuations (an active non-equilibrium state). Once this relationship is quantified, it will provide insight on the basic physics of the biological processes occurring in living cells. We aim to use both calibration methods to verify accurate force measurements in living cells to characterize their non-equilibrium fluctuations. |
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G60.00023: Organic Solar Cells: Construction and Characterization Jake Keiper, Marian Tzolov An Organic Solar Cell is a type of photovoltaic cell that uses organic polymers for light absorption and charge transport. Organic Solar Cells have benefits such as being light weight, flexible, conforming to variety of surfaces, and potentially inexpensive and disposable. Different polymers are used in these cells to alter the band gap and utilize different parts of the solar spectrum. Structure can vary in the sequence of the layers, such as the cells being regular or inverted cells. We will present results on regular cells with hole injection layers PEDOT:PSS and PLEXCore, and active layers of P3HT, PCPDTBT, and PCBM (C-60). The interaction of the HIL with the solvent of the subsequent polymer blend solution was studied, as well as other aspects of solution deposition. We show that if this process is not well controlled substantial electrical shorts form in the device deteriorating the photovoltaic performance. Methods of characterization include Current-Voltage characteristics and Impedance spectroscopy, which give a great insight on the electrical processes in the devices. Understanding all the parameters and characterizations of the devices allows us to improve and achieve reproducibility in the devices. |
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G60.00024: Soda Wall (Testing the Strength and Force of Sand Filled Plastic Bottle-Bricks) Kaitlyn Kelly Gonzalez, Jency Pricilla Sundararajan Every year millions of people lose homes through natural disaster or armed conflict. Safe, inexpensive homes can serve as an optimum alternative for places that are highly prone to such calamities. This project will help resolve the crisis by building houses reusing trash, namely two-liter plastic bottles filled with sand or dirt. It will also help to reduce some of the waste that is plaguing the planet by putting it to a constructive use. The variables tested during this project were the strength of the bottles as bricks using either sand or dirt as well as the durability of the wall against the force of different bullets fired from a firearm. The bullet sizes tested for this project were .40 caliber, .22 caliber and a 9 millimeter bullet. Using the amount of energy read by an infrared thermometer we determined the velocity of the bullet as it hit the wall and thus could determine the force of the projectile at the moment of impact. This enabled us to easily determine how deep the bullet penetrated the wall, without risking further damage to the wall. We tested the same bullets against both a wall with bottles filled with sand and a wall with bottles filled with dirt to similar results. |
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G60.00025: Analysis of the magnetic and ringing properties of nickel-zinc-ferrite for use in pulsed nuclear magnetic resonance applications Richard Korneisel, Cajetan Nlebedim, Neelam Prabhu Gaunkar, David Jiles Pulsed nuclear magnetic resonance (NMR) techniques are used in the oil industry to survey land for hypogeous fluid deposits. Inductive sensors act as both transmitters and receivers to detect these deposits and often require a magnetic core to enhance the quality of signals recorded. Ideal magnetic properties of a core include a high magnetic permeability and saturation magnetization. However, it is also observed that the magnetic core responds to the input signals producing oscillations which interfere with the NMR measurements, thus necessitating reduction of ringing amplitude and increase in peak linewidth. If not suppressed, the ringing of the core would cause significant noise in measurements and render the device inoperative for some time. To meet the criteria of the application, sintered nickel-zinc-ferrite (Ni-Zn ferrite) powder set in epoxy were chosen for the core material. The relative amounts of nickel and zinc were varied and the compositional effect on magnetic and ringing properties were analyzed to determine an optimal core composition. In this work, an analysis of the magnetic and ringing properties of Ni-Zn ferrites suited for pulsed NMR systems will be presented. |
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G60.00026: Electrochemistry of DNA Nucleobases, Nucleosides, and Nucleotides and their Computational Analysis under Aqueous Condition Gakyung Kwon, Ryan Wong, Seung Soon Jang The general electrochemistry of deoxyribose nucleic acid (DNA) was investigated for real-life electrochemical applications. For a systematic approach in electrochemical analysis, DNA was subdivided into its structural units – nucleobases, nucleosides, and nucleotides. Additionally, reduction potentials were utilized as dependent variables calculated via density functional theory (DFT) with PBE0/6-31G**+ to determine the electrochemical characteristics of DNA and better highlight the contributing electrochemical effect caused by the addition of deoxyribose and phosphate group. Furthermore, considering a real-life application where solvent may be present, PBF calculations using the default solvent–water –were executed. Solvation condition was considered at every level of computation to identify the influence of chemical reactions originated from the presence of solvent and results were examined in contrast to the redox potentials computed under vacuum condition. Furthermore, the results were once again compared to those using EC-DMC as a solvent to analyze the effect of different solvents on redox potentials of DNA subparts. |
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G60.00027: Spectral Analysis of Low-Energy 22- and 23-atom Boron Clusters using DFT Ryan Lashley, Hikmat BC, Christopher Varney Previous studies using density functional theory have shown that 22-atom boron clusters tend to prefer a three-dimensional double ring structure in its neutral, cationic, and anionic states while 23-atom boron clusters prefer planar structures. These results agreed with a pattern from smaller boron clusters where clusters with an odd number of atoms tend to form planar structures while clusters with an even number of atoms tend to form the double ring structures. Here we present the density of states, infrared, Raman, and vibrational spectra for B22 and B23 clusters. |
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G60.00028: Best secular light curve for comet Hale-Bopp and implications for dust production rates Nathan Lastra, Anthony Curtis, Maria Womack, Olga Harrington, Kacper Wierzchos, Nicholas Ruffini, Charles Mentzer, Chloe Jackson, David Rabson, Timothy Cox, Isabel Rivera, Anthony Micciche We present an algorithm for reducing scatter and increasing precision in a comet light curve. We processed apparent magnitudes of comet Hale-Bopp from 17 experienced observers (archived with the International Comet Quarterly), correcting for distance from Earth and phase angle. Different observers tend to agree on the difference in magnitudes of an object at different distances, but the magnitude reported by observer is shifted relative to that of another for an object at a fixed distance. We estimated the shifts with a self-consistent statistical approach, leading to a sharper light curve and improving the precision of the measured slopes. The final secular lightcurve for Hale-Bopp ranges from -7 au (pre-perihelion) to +8 au (post-perihelion) and is the best secular light curve produced to date for this “great” comet. We discuss Hale-Bopp’s lightcurve evolution and the possible physical implications and usefulness of this light curve for comparisons with other future bright comets. We then assessed the suitability of using secular lightcurves to characterize dust production rates via the quantity "Afp" in Hale-Bopp and other dust-rich comets. We find that this method produced results congruent with more rigorously derived measurements for Hale-Bopp when it was pre-perihelion. |
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G60.00029: Genetically engineered human ferritins over expressed in E. coli with various H/L chain ratios: A comparative Mossbauer study of their iron cores. Thomas Longo, Arthur Viescas, Georgia Papaefthymiou, Lara Varden, Britannia Smith, Fadi Bou-Abdallah, Paolo Arosio Ferritin is responsible for the storage and regulation of iron in living organisms. Mammalian ferritin consists of a spherical, hollow protein shell composed of 24 amino acid subunits of two forms: H and L. Iron is bio mineralized within the hollow protein as ferrihydrite. In our studies the electronic, magnetic and morphological properties of the ferrihydrite core are studied via Mossbauer (300<T<4.2K) and TEM measurements. Genetically engineered human ferritins overexpressed in E. coli, with controlled H/L ratio, are investigated. Herewith we present data on two samples: an H-rich ferritin with 21H- and 3L-chains and an L-rich ferritin with 2H- and 22L-chains. There is one ferroxidase center, which catalyzes the Fe2+→Fe3+ oxidation, per H-chain, while L-chains lack a ferroxidase center. The temperature profile of the Mossbauer spectra is analyzed in order to determine the blocking temperatures of the cores, which inform of their relative magnetic anisotropies and therefore their relative degree of crystallinity. This study aims to correlate the degree of crystallinity with the number of ferroxidase centers on the protein. |
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G60.00030: Selective Adsorption of CO2 / CH4 in a Graphene Pocket Brandon Markham, Silvina Gatica Abstract: The goal of this work is to predict the selective adsorption of CO2 from a 1:1 mixture with CH4 into the pocket region between a slotted layer of graphene fixed above a graphite surface. Molecular dynamics in a canonical ensemble was used to simulate this adsorption. In the system, methane is modeled as a single, spherical Lennard-Jones (LJ) fluid. Carbon dioxide is modeled by a three site, quadrupole, rigid body LJ fluid. The slits in graphene are made by cutting and deleting carbon atoms from the lattice within a region of specified width, and the reactivity of the edges are not taken into account. Graphite is modeled in the walls perpendicular to the z-direction by a 10-4-3 LJ potential. Trials at 273K are performed with cutting regions varying from 3Å-15Å. Simulations were also conducted for a cutting region held at 4Å, and the temperature varied. Results show that there is not significant selectivity in the pocket region, though both gases are highly attracted to the region. Edge effects, such as narrow slits, and low temperature tend to increase initial selectivity, but once equilibrium is reached, little selectivity is observed. |
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G60.00031: Morphology & Ferroelectric Properties of Organic Films Luis Martinez, Xiaoshan Xu, yuewui yin In this research study, a thin film of a ferroelectric material, croconic acid (C5O5H2), was grown using a high vacuum sputtering deposition system and afterwards investigated to obtain its properties in a real capacitor device structure. The organic material, croconic acid, was selected in order to ultimately establish organic ferroelectric devices through the fabrication of multilayer thin films with multiferroic properties. Organic materials are highly favorable due to their distinctive advantages over inorganics in terms of flexibility, cost efficiency, and sustainability. The potential of organic materials to become viable material alternatives to the inorganic counterparts hinges on the availability of strategies to fabricate thin films with defined structure and morphology on a large scale. |
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G60.00032: Study of the Role of Disorder in SmB6 with Samarium Vacancies and Alloys of SmB6 Dmitri Mihaliov, Yun Suk Eo, Alexa Rakoski, Juniar Lucien, Priscila Rosa, Cagliyan Kurdak Samarium Hexaboride (SmB6) is a unique strongly correlated electron material that hosts topologically protected surface states and a truly insulating bulk. With our newly developed inverted resistance measurement method, we were able to obtain bulk transport data below the temperature wherein surface conductivity becomes dominant. Through this data we find strong evidence that the bulk is immune to disorder due to identical activation energies in samples with varying vacancies. At temperatures below 2.5 K, however, there is a plateau present which functions almost independent of temperature and whose magnitude seems dependent on the amount of samarium vacancies present in the sample. We hypothesize that some form of extended defects may be responsible for this behavior. We have characterized the crystals using X-ray diffraction, Auger, high-resolution TEM, energy dispersive X-ray spectroscopy, and Vicker’s hardness measurements. With increasing vacancy concentration, we found a significant reduction in the hardness of SmB6 crystals and direct evidence for twinning in X-ray studies, confirming the presence of extended defects. |
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G60.00033: Active Self Assembled Monolayers investigated via Atomic Force Microscopy Chadd Miller, Tyler Adams, Brian Evans, Indrajith Senevirathne Self-Assembled Monolayers (SAMs) of thiols Au(111) are one of the useful bases for designing many NEMS (Nano Electro Mechanical Systems) and MEMS (Micro Electro Mechanical Systems) focused on diverse array of applications. Thiol based SAMs from Mercapto-1-undecanol, an aromatic dithiol, and Amino -1- Hexane thiol-hydrochloride were synthesized in stabilizing ultra-pure ethanol solvent on Au(111) coated mica to create both negative and positive surfaces. These were investigated via Atomic Force Microscopy (AFM) with and without functionalized tips to assess their surface packing, consistency, charge/energy characteristics. These were further investigated with the contact angle measurements for macroscopic coverage and their long range surface reactivity on the substrates. Discussion of the results obtained compared with the existing literature will follow. |
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G60.00034: Exoplanetary Atmospheres in the Near I.R. Spectrum: Departures from a Homogeneously Distributed Gas Assumption Lauren Miller, Gael Roudier, Mark Swain Radiative transfer models that are calibrated for exoplanet transit use both well-understood atmospheric mechanisms and measurements from our own solar system to set up the relative abundances of gases contributing to the observed total spectral modulation. This procedure helps to narrow down the possible composition of exoplanet atmospheres. However, existing retrieval codes depend on a uniform vertical mixing ratio (VMR), in order to cut computation costs. Departures from an atmosphere where gas is homogeneously distributed may reflect the effects of chemical quenching and photochemistry. |
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G60.00035: A bursting assay for Giant Unilamellar Vesicles containing gangliosides Fernanda Murillo, Aurelia Honerkamp-Smith We know that certain cell types are constantly exposed to flow, that these cells sense flow and that flow is essential for normal function in these cells. We want to study the effect that flow has on membrane proteins. Our lab creates phospholipid bilayers in the form of Giant Unilamellar Vesicles (GUV) in order to investigate the effect of flow on membrane proteins. We break the vesicles using a saline solution; the vesicles sink and rupture on the glass surface to form a flat sheet (splat), which we refer to as a supported lipid bilayer (SLB). We then apply a flow to the SLB to see its effect on membrane proteins.This work studied how to optimize the breaking conditions of GUV to use the SLB to study the effect of flow. In order to characterize splatting conditions, we took a movie of the vesicles breaking on a glass surface and developed a Python program to detect the vesicles in each frame of the movie to observe the properties of the splatting. We found that as expected, there was a decrease in vesicle count through time, increasing gangliosides did not have an observable effect on splatting, and cleaning the slides with plasma did not make the vesicles splat faster. |
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G60.00036: Statistically Determining the Shape of a Glowing Object Zakary Noel, Suzanne wheeler, Keeley Fairchild, Daniel Dove, Gabrianna Escamilla, Nurul Azam, Cristian Bahrim Preliminary experiments have shown that is possible to determine the shape of a glowing object with polarimetric measurements. Introducing a new quantitative method of interpreting our data, we have expanded upon our proof of concept by implementing statistical analysis to differentiate between regular polygons of n sides. By refining our experiment and creating a well-calibrated system, we have identified a method for extracting the best possible measurements from our setup so that we may compare them against a control signal. Improving upon the data acquisition process, we use an improved optical setup to focus the contour of the glowing object on the light sensor. Combined with calibration data suggesting an ideal measurement window, we expect a reduction in error for the experiment stemming from issues with equipment. Based on trends in the distribution of spreading, we now believe that we can construct unique profiles for each shape and use them to characterize the signals that we collect. From this result, we can relate the shape of the object to the theoretically predicted ratio of the area of luminosity between a probe signal and the control signal. |
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G60.00037: Controlling Atomic Excitation with Frequency-Modulated Lasers Kristen Oldja, Matthew Wright
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G60.00038: Ambipolar transport in CVD grown MoSe2 monolayer using an ionic liquid gel gate dielectric Deliris Ortiz, Idalia Ramos, Nicholas Pinto, Mengqiang Zhao, Alan Johnson Ambipolar charge transport was observed in CVD grown crystalline MoSe2 monolayers using an ionic liquid gel gate dielectric in a field effect transistor configuration. Gold electrode contacts with the device resulted in Schottky barriers that were higher for electron transport. Applying a gate voltage lowers this barrier allowing electrons and holes to flow through the same channel at room temperature. The threshold voltage for electron transport was lower than that for holes indicating strong electron doping or Fermi level pinning to the conduction band. The high specific capacitance of the ion gel permitted device operation at low applied voltages. Preliminary calculations for the electron (hole) mobility was found to be 0.2 (0.1) cm2/V-s and the on/off ratio was ~106 for holes and electrons. The device was successfully tested in a resistor loaded inverter circuit and showed a gain of ~3. The ambipolar feature of MoSe2 makes it an excellent candidate for use in low power consumption flexible complimentary logic circuits. |
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G60.00039: Molecular Organization in Cell Membranes Austin Osby, Theja De Silva Cell is the fundamental building blocks of all living matter. The cell consists of cytoplasm enclosed within a membrane where cell membrane is composed of lipids and protein molecules. Lipid molecules form a bilayer structures in cell membrane when they are in aqua environments. All membrane proteins carry out their cellular functions while they are sitting at membrane sites. Due to the collective behavior of these molecules, they undergo self-organization and form various structures, such as phase separation and domain formations. We use a thermodynamics approach to study three-component molecular organization by modeling the interaction between molecules using spin variables. Converting the interacting spins into an effectively non-interacting variables using a mean-field theory, we calculate the Helmholtz free energy (HFE). Then by investigating the HFE, we construct the phase diagram and study the molecular organization in cell membranes. |
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G60.00040: Localization in Disordered Lattices of Classical Magnets Jordan Pack, Erik Henriksen We have constructed a system of freely rotating 1” permanent bar magnets that can be organized in arbitrary lattices. Here, we looked for classical localization in a square lattice (of 7 x 22 sites) by driving one magnet on the boundary and observing the motion of the others in response. We began with a regularly spaced square lattice, and then looked at disordered lattices formed by introducing geometric disorder to the square lattice by displacing lattice sites by fixed distances in random directions. With larger displacements, which we characterize as larger disorder, we find that motion is localized to small regions about the moving magnet. We will share our progress in studying the dynamics of these lattices and the localization in disordered lattices. |
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G60.00041: Radiation Shielding Capabilities of Glasses with Potential Applications in Spacecraft and Laboratories Greg Palmer, Blake Bailey, Collin Wilkinson, firdevs duru Radiation shielding glass is a good candidate to be used in the future manned spacecraft missions, as well as in radiation intensive laboratory environments. This study investigates radiation shielding properties of a number of semiconducting glass compositions produced at Coe College. To test radiation shielding abilities, Geant4 simulations were created where protons, electrons, and neutrons, with energies ranging between 1 keV and 100 GeV, were fired into semiconducting photovoltaic amorphous materials. The data were converted into stopping power, which correlates with the shielding capabilities of these glasses. In this system of analysis 0.4TeO2-0.6V2O glass provides greater than a 13% increase in stopping power when compared to other glasses tested at 8.4 eV cm2/g. The post-shielding distributions, which show considerable variations, are also provided. Comparison with aluminum and water suggests that some of these glasses are good candidates for missions requiring radiation shielding. Of particular interest is the applicability of these materials to manned missions to Mars in order to shield astronauts from dangerous solar winds and galactic cosmic rays. |
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G60.00042: Diurnal variability of total suspended particulate, PM 2.5, by using Sensidyne Nephelometer Luke Parkhurst, Anthony Barinelli, Raymond Miller, Chelsea Bitter, Rudra Aryal This research will be viewing the air quality around the South-Western towns of New Hampshire; Keene, Rindge, and Jaffrey, by using the Sensidyne Nephelometer. It uses the light scattering techniques to determine the particle concentration. By measuring heavier traffic areas, these tests can view a diurnal variation of pollution around the area. Using this Nephelometer, the average particle concentration during the morning, afternoon and evening were observed and found a significant concentration of particles during the heavy traffic period in Jaffrey than in other areas. The results show both traffic and geography of the location impact on the concentration air particles or dust particles. |
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G60.00043: Infrared Response of a Quasi-Crystalline Filter Samantha Pedek The cosmic microwave background (CMB) is the left over radiation from the Big Bang. Studying this faint microwave signature gives insight into the conditions of the early universe. In order to make precision measurements of the CMB polarization, cryogenic detectors maintained at ~0.1 Kelvin are needed to operate the detectors. Background infrared radiation can warm the instrument and degrade its performance. This thermal radiation can be mitigated by using a series of infrared blocking filters. Traditionally, infrared metal mesh filters consist of several layers of a translationally symmetric tiling (e.g. squares or hexagons) are used to block radiation in large apertures. This approach can lead to diffraction at large angles, which can create a pattern in the angular response. This decreases the angular resolution and beam symmetry, which is vital for polarimetry measurements. This study uses a rotationally symmetric tilling of pentagons which cannot be tiled in two dimensional translational space, also known as a non-periodic quasi-crystal. The quasi-crystalline filter has been fully designed and is awaiting fabrication. |
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G60.00044: Cavity Enhanced Raman Spectroscopy of Optically Trapped Aerosols Lars Poppy, Jackson Kock Small transparent particles can be suspended in air using a laser to create an optical trap. It has been observed that the intensity of the laser affects the position of trapped aqueous aerosol droplets. The stable positions that the droplet varies between are caused by a resonance of the light from the trapping beam on the surface of the droplet, called Whispering Gallery Modes. When this resonance occurs, forces acting on the droplet cause it to move. To determine an understanding for this behavior, the droplet’s position is correlated to the Raman scattered light. The spectrum of light scattered from the droplet’s surface produces peaks in intensity, known as Cavity Enhanced Raman Spectroscopy. Certain properties of the droplet, such as the diameter and refractive index, can be harvested by analyzing the location and spacing of the peaks. This analysis gives precise measurements of the droplet’s radius, which can be used to determine if a resonance occurs when the droplet moves. |
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G60.00045: Small-scale fluctuations of cytoplasmic vesicles Danielle Posey, Paris Blaisdell-Pijuan, Wylie Ahmed Intracellular environments are dynamic spaces filled with various particles moving in every direction. Included in this diverse group of particles are vesicles, which are involved in transport of molecular cargo throughout the cell. Vesicles move in either a directed or non-directed fashion, often depending on cytoskeletal proteins such as microtubules, actin filaments, and myosin-II motors. However, it is uncertain exactly how these cytoskeletal proteins affect the mobility of vesicles in the cytoplasm since they could both facilitate and impede motion. Here we show that vesicle motion is significantly affected by cytoskeletal elements. We found that myosin-II has the largest impact on vesicle mobility: when present, it increases the effective diffusivity and decreases the duration that vesicles spend undergoing non-directed motion. We also found evidence that actin filaments act as a barrier to vesicle motion, trapping them in the cytoplasm and blocking potential pathways for directed and non-directed motion. Our study suggests that by modulating myosin-II activity in the cytoplasm cells can tune the mobility of vesicles. This allows a mechanism for cells to dynamically tune the cytoplasmic environment in space and time. |
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G60.00046: Graphene Synthesis, Transfer, Characterization, and Application Kathrine Quiros, Madison Berger, Alex Koch, Michael Lambert, Estifanos Mekuria, Daniel Solar, Lan Wei, Howard Chen, Michelle Chen Graphene’s unparalleled electrical and physical properties hold immense promise in biomedical applications including sensing and drug delivery. However, the ability to synthesize and transfer large-area graphene onto substrates to interface with biological systems remains a challenge. Furthermore, graphene’s potential cytotoxicity is yet well understood and limits downstream biomedical applications. We report here the synthesis of large-area single and a few layers of graphene on copper via chemical vapor deposition. The roles of growth time and hydrogen were systematically investigated. After synthesis, the graphene was transferred onto silicon and glass substrates while maintaining the integrity of the synthesized graphene. The graphene samples were characterized using scanning electron microscopy, Raman spectroscopy, and optical imaging to qualitatively and quantitatively assess the coverage and quality of the graphene. Finally, the cellular impact of graphene on glass was evaluated in fluorescently-labeled heart myocytes (H9C2 cells) by imaging and biochemical assays. We found that large-area single layer graphene enhances cell growth, and exerts no apparent cytotoxic effect. Large-area graphene is thus biocompatible and facilitates further biomedical integrations. |
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G60.00047: Graphene Synthesis, Transfer, Characterization, and Application Kathrine Quiros, Madison Berger, Alex Koch, Michael Lambert, Estifanos Mekuria, Daniel Solar, Lan Wei, Howard Chen, Michelle Chen Graphene’s unparalleled electrical and physical properties hold immense promise in biomedical applications including sensing and drug delivery. However, the ability to synthesize and transfer large-area graphene onto substrates to interface with biological systems remains a challenge. Furthermore, graphene’s potential cytotoxicity is yet well understood and limits downstream biomedical applications. We report here the synthesis of large-area single and a few layers of graphene on copper via chemical vapor deposition. The roles of growth time and hydrogen were systematically investigated. After synthesis, the graphene was transferred onto silicon and glass substrates while maintaining the integrity of the synthesized graphene. The graphene samples were characterized using scanning electron microscopy, Raman spectroscopy, and optical imaging to qualitatively and quantitatively assess the coverage and quality of the graphene. Finally, the cellular impact of graphene on glass was evaluated in fluorescently-labeled heart myocytes (H9C2 cells) by imaging and biochemical assays. We found that large-area single layer graphene enhances cell growth, and exerts no apparent cytotoxic effect. Large-area graphene is thus biocompatible and facilitates further biomedical integrations. |
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G60.00048: Introducing Quantum Causality Threshold into General Relativity Dmitri Rabounski, Florentin Smarandache, Larissa Borissova An ultimate case occurs as soon as the space rotation velocity reaches light velocity. If particles A and B are located in the space entirely in this ultimate state, neither A nor B can be the cause of events located “over” the spatial section. So in this ultimate case the entire space-time is in a special state called the Quantum Causality Threshold. Particles located in General Relativity’s space-time reach the Quantum Causality Threshold as soon as the space rotation reaches light velocity. Quantum Causality Threshold is impossible if the space does not rotate (holonomic space), or if it rotates at a sub-light speed. Thus, the Quantum Causality Threshold has been introduced into General Relativity. |
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G60.00049: Development of a Solid State NMR Physics Laboratory Russell Ramirez, Rosa Cardenas We report on the progress of the development of a new physics laboratory at the University of the Incarnate Word (UIW). This laboratory will be the first physics research laboratory at this institution. It will include a new solid state NMR experimental setup. This experimental setup will be comprised of a 400 MHz cryogen free, superconducting magnet manufactured by Cryogenic. It will also include a Tecmag Redstone NMR Spectrometer. This spectrometer is very flexible and therefore many different samples may be analyzed. For example, we plan to analyze the superconducting transition of the iron-chalcogenide FeTeSe and the hydrogen storage characteristics of metal hydrides. |
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G60.00050: Galactic Cosmic Radiation Shielding Utilizing Active and Passive Methods Matthew Sailer, Heide Doss Radiation shielding is essential to future missions of space exploration due to increased exposure to radiation harmful to humans. One of the most damaging and hardest types of radiation to stop consists of High Atomic Number and Energy (HZE) particles in Galactic Cosmic Radiation (GCR). These particles are fully ionized and travel at near light speeds. The most dangerous of these is iron nuclei. Many shielding options have been proposed in both active and passive categories of shielding. This research explores several previously proposed methods of both active and passive shielding and seeks to demonstrate why active shielding is more advantageous than passive shielding. Active shielding, however, cannot fully protect against all types of radiation, so a combination of active and passive shielding must be used. A combination of active and passive shielding is proposed in an attempt to maximize the deflection of radiation, minimize the produced secondary radiation, create a net thrust from the redirected particles, and account for space being a diffuse plasma. |
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G60.00051: Designing and 3D Printing Lab Equipment Whitley Sapp, Cody Emberton, Bryce Kapitzky, Casey Watson We use Autodesk Fusion 360 and a MakerBot Replicator 5th Generation 3D printer to design and manufacture lab equipment. Using this process, we can create various instruments at much lower cost than retail value. This allows us to provide excellent learning experiences for science students at reduced cost, without sacrificing quality or precision. |
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G60.00052: Calculating Boosted Higgs Boson Production as a Function of Couplings to Top Quarks, Bottom Quarks, and Vector Bosons Jesus Serrano, Jason Nielsen In 2012 the Higgs boson was discovered at the Large Hadron Collider (LHC) at |
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G60.00053: Building a Custom Microscope – An advanced lab to study Brownian motion Hunter Seyforth, Wylie Ahmed The process of building a microscope from scratch provides the students with a basic understanding of each individual component of the optical set-up. Subsequent digital image recording and data analysis provide an introduction to image processing and statistical analysis. Our goal is to create an advanced laboratory module for students to build an optical microscope, calibrate it, and make precise measurements of Brownian motion. We constructed an optical microscope based on the design by Kemp et al. (arXiv:1606.03052). Then, using a 40x objective, we study the Brownian motion of 1 micron colloidal particles. A digital camera is used to record videos of colloidal motion, ImageJ is used to post-process the images, and Matlab is used to calculate the diffusion coefficient of the particles. We use these measurements as an opportunity to explore error quantification in measurements of Brownian motion (Catipovic et al. AJP 81(7) 2013). Our advanced lab module is intended to be an introduction to physics research, fortify concepts from optics and statistical physics, and give students hands-on experience in building optical systems and analyzing noisy data. |
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G60.00054: Hierarchical Bayesian Modeling Karan Shah The grav |
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G60.00055: Phase Stability of bcc MgScY via Cluster Expansion and Monte Carlo Methods Adam Shaw, Gregory Pomrehn, Aurora Pribram-Jones, Patrick Conway, Michael Ferry, Kevin Laws, Lori Bassman The MgSc disordered bcc lattice has the potential for light weight, high strength applications, but is only stable far above room temperature. It is thought that the addition of ternary or quaternary components to the binary system could stabilize this phase at accessible lower temperatures. However, the search space for possible ternary candidates is too large to fully explore experimentally. Thus, to guide the physical alloy development, computational methods are applied to determine the relative phase stability of the MgSc binary to the model ternary, MgScY. A lattice cluster expansion model is developed based on density functional calculations, and finite temperature thermodynamic behavior is computed from Monte Carlo simulations. The method may be applied to further ternary components, elucidating elements that best lower the stable temperature regimes of the bcc phase. |
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G60.00056: Investigation of Test Fixtures and Measurement Configurations on the Impedance of ‘Moso’ and ‘Red Margin’ Bamboo James St. John, Todd Freeborn The electrical impedance of bamboo over the frequency range of 20 Hz to 100 kHz was studied. The main objective of this work was to develop a method to reliably and reproducibly collect impedance measurements and study potential sources of error due to the test configuration. Similar research has investigated the impedance of fruits and vegetables to monitor for physiological changes. Several different test fixtures were explored yielding contact resistance (introduced between the test leads and bamboo sample) is a significant problem for taking consistent impedance measurements and the impedance of the bamboo is inversely related to its moisture content. |
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G60.00057: Multidisciplinary REU site at Cleveland State University: Synthesis, Assembly, and Characterization of Soft Matter. Kiril Streletzky, Jessica Bickel Researchers at Cleveland State University’s Department of Physics and Department of Chemical & Biomedical Engineering collaboratively study the unique properties and applications of soft matter materials. In 2017, these departments joined forces to start a new NSF-sponsored Research Experiences for Undergraduates (REU) site. The objective of our site is to involve undergraduate physics and engineering majors in meaningful interdisciplinary research projects within soft matter science and engineering. A primary focus of our site is to encourage students to continue in STEM fields as either graduate students or workforce members. CSU’s focus on Engaged Learning has cultivated a strong culture of support for undergraduate research, and REU participants benefit from this culture. Students receive one-on-one mentoring from experienced faculty and participate in a variety of professional development opportunities. This poster will give an overview of the student research accomplishments and program challenges encountered in the first year of our multidisciplinary REU. It will also discuss the benefits of the experience to both students and faculty mentors. |
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G60.00058: Control and Stabilization of Frequency and Intensity of an External Cavity Diode Laser Kidan Tadesse, Matthew Wright We are enhancing a magneto optical trap toward collision students with ultracold atoms using frequency chirped laser light. Toward this goal, we have developed an intensity servo feedback circuit to control the intensity of the incoming laser beam and a frequency-lock control system that results in stabilization of the laser's frequency to an atomic-line. We will discuss our progress in further improving the stability of our magneto-optical trap. |
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G60.00059: A Low-cost Microfluidic Device to Study Nonequilibrium Physics of Colloids Monika Tadrous, Abi Mendez, Wylie Ahmed Microfluidics is a field of research that involves manipulating micron-scale volumes of fluids. Microfluidic devices have many applications; in our lab, we use microfluidic devices to study active colloidal particles. In this study we develop a low-cost microfluidic device and use the device to study the dynamics of microscopic particles. To create a low-cost microfluidic device in the lab, we implement a method pioneered by Michelle Khine at UCI which utilizes inexpensive equipment. Materials needed to build a functioning chip are: an oven, a handheld Corona discharger, Shrinky-Dinks, and polydimethylsiloxane (PDMS). In a matter of minutes, a complete microfluidic device can be made. We use the devices to study the nonequilibrium dynamics of active self-propelled colloids. Active colloids are spherical particles that have a hematite cube embedded in them to create a Janus particle. These active colloids, under equilibrium conditions, undergo Brownian motion; however, when the particles are illuminated with blue light, they self-propel and generate active motion. We use microfluidic devices to study the dynamics of active colloids under flow. Our low-cost microfluidic devices allow us to study the microscale motion and force dynamics of active colloids. |
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G60.00060: Light Scattering Characterization of Anisotropic Nanoparticles Dan Terrano, Ilona Tsuper, Victor Rudoy, Kiril Streletzky Depolarized dynamic light scattering (DDLS) can be used to measure the rotational and translational diffusion of nanoparticles suspended in solution. The particle size, shape, diffusion, and interactions can then be inferred from the DDLS data using various models of diffusion. Incorporating the technique of DDLS to analyze the dimensions of easily imaged elongated particles, such as Iron (III) oxyhydroxide (FeOOH) spindles and gold nanorods, allows testing of the models for rotational and translational diffusion of elongated particles in solution. This study can further be used to help better interpret DDLS data on hard-to-image anisotropic soft matter systems such as micelles, microgels, and protein complexes. This study focused on FeOOH Spindles and gold nanorod particles. The light scattering results on spindles using the basic model of non-interacting prolate ellipsoids yielded results within 17% of the SEM measured dimensions. The dimensions of gold nanorod obtained from the straight cylinder model of DDLS data provided results that varied depending on the solvent used and the aspect ratio. |
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G60.00061: Synthesis Optimization and Characterization of Polymeric Microgels Samantha Tietjen, Samantha Hudson, Kiril Streletzky Microgels are spherical particles suspended in solution, comprised of crosslinked polymer chains. Due to the amphiphilic property of the parent polymer, microgels display a temperature dependent volume phase transition (de-swelling), and thus have the potential to be used for drug delivery. Microgels were synthesized using a polysaccharide polymer and cross-linker, in a surfactant solution. Synthesized particles were characterized using dynamic light scattering (DLS) for temperature and angular dependence to study their shape and determine the apparent hydrodynamic radius (Rh) of the swollen and de-swollen states. Previous studies suggest that increasing the concentrations of the chemical cross-linker reduces Rh and the de-swelling ability. Initial microgel synthesis revealed a dependence of Rh on microgel concentration in samples, requiring a correction factor during analysis. Primary experiments focused on the variation of cross-linker concentration ratios. Increasing the ratio from 1 to 30 causes Rh to decrease from 150 - 190 nm at 25oC, and from 65 - 95 nm at 50oC. Ratios from 30 to 50 resulted in swelling from 70 nm at 25oC to 165 nm at 50oC. At a ratio of 60, an apparent bulk gelation occurred. |
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G60.00062: Enhancing outreach and building community in the University of Alaska Fairbanks physics department through an active chapter of the Society of Physics Students Riley Troyer The Society of Physics Students (SPS) is a national organization dedicated to “helping students transform themselves into contributing members of the professional community.” The University of Alaska Fairbanks (UAF) has had a local SPS chapter for many years. Recently, the chapter has grown significantly and become much more active. In this poster we will showcase the opportunities and outreach that our chapter has provided to UAF students and the Fairbanks community within the last several years. Through these activities we have worked to create a strong undergraduate physics community at UAF and raise the public awareness of the department through community outreach. It is our hope that this poster will offer ideas and inspiration to other physics departments and SPS chapters across the nation. |
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G60.00063: Impacting the field of physics by creating a pipeline for undergraduate physics students to work in Congress Riley Troyer When it comes to science policy, undergraduate students are rarely mentioned, despite having the necessary skills for success in the field. In this poster, I will use my experience as a physics undergraduate and intern for the majority side of the U.S. Senate Committee on Energy and Natural Resources, to highlight the need for more scientifically trained people in Congress. I will provide arguments as to why undergraduate physics students offer a solution to this problem. I will also show how that solution can be implemented through the funding of more policy internships for physics students. Finally, I will demonstrate how a relatively small investment in this area can have large impacts on the field of physics. |
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G60.00064: Examination of external cavity diode lasers’ stability by demonstrating optical beat notes through optical heterodyne experiments STAVRINI TSANGARI The main goal of our optical heterodyne experiments is to examine the stability of our own in house-built external cavity diode lasers (ECDL) under different locking methods. In any laser system, it is of a great use to be able to identify and remove noise sources and narrow the linewidth. |
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G60.00065: Integrating Fluid Dynamics into the Undergraduate Physics Curriculum Jason Turner, Scott LaBrake Fluids permeate all of human existence, and fluid dynamics serves as a rich field of research for |
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G60.00066: Measuring mitochondrial transcription factor A using graphene transistors Agatha Ulibarri, Megan Bestwick, Michael Crosser Graphene, an allotrope of carbon in which atoms are arranged entirely within a two dimensional sheet, has been shown to be a sensitive probe for biological activity. We report on efforts to functionalize graphene with mitochondrial DNA which should make the devices sensitive to mitochondrial transcription factor A (TFAM). |
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G60.00067: Device for Measuring the Seebeck Coefficient Jesus Velasquez, Pei-Chun Ho Applying a temperature gradient across a conducting material will create an electric potential difference across the corresponding material. This phenomenon is called the Seebeck effect, and a given material’s response is determined by the Seebeck coefficient, which is defined as the negative ratio of the electrical potential to the temperature difference across the material. We are interested in characterizing the Seebeck coefficient of intermetallic compounds, from 10K-300K, and have constructed a device to measure the corresponding physical parameters. Using a sample of nickel 201 alloy, data from device testing showed moderate accuracy within a limited temperature range, with large discrepancies observed below 60K. This error possibly stems from the limited measuring capability of a lab built type-T thermocouple in the low temperature range. Therefore, extending the accuracy and reliability of the device to measure over the 10K-300K range will require modifications to the temperature sensing elements with subsequent tests. |
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G60.00068: Production of Ethanol from Sequestered Carbon Dioxide Andrea West, Selby Jakachira, Casey Watson, Paris Barnes We built an anoxic environment for methanogens, which convert hydrogen gas and carbon dioxide into methane. We then use the methane along with water and other catalysts to produce ethanol. Our ultimate goal is to create carbon-neutral fuel with the Carbon Sequestration Center in Decatur, Illinois. |
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G60.00069: Room Temperature Characterization of MEMS Devices: Effects of Nearby Solid Boundary Lucas Wilkins, Colin Barquist, Yoonseok Lee Micro-electro-mechanical-systems (MEMS) are common devices used in consumer technologies and scientific research. MEMS devices are implemented to study quantum fluids by analyzing their mechanical resonance when submersed in fluid. Fundamental equations that describe these devices provide significant information, allowing for quantitative analysis of the oscillators’ resonance. In this study, the effects of damping on the harmonic oscillators are reviewed. Comparisons are made between MEMS devices with and without a substrate. These comparisons are made by varying the pressure of N2 gas and examining the resulting resonance frequencies. Examination of the results suggests that a damped harmonic oscillator without a close boundary experiences a changing rate of damping with pressure and that an oscillator with a close boundary experiences a linear relationship between damping and pressure when submersed in a classical fluid. |
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G60.00070: A GUI to study Active Matter Lovell Willmore, Nicholas Brubaker, Wylie Ahmed Active matter is a field of research that studies the phenomena and complex behavior emerging in systems of interacting objects. It has been used to describe schools of fish, flocks of birds, and even things as small as molecules in living cells. The Vicsek Model is a canonical model of active matter—composed of locally aligning, self-propelled particles—that has potential to be applied to a wide variety of topics, and could attract aspiring new students to science. However, since the field of active matter has only recently developed over the past two decades, it is largely inaccessible to students outside the field. To address this problem we have developed a Graphical User Interface (GUI) that simulates the Vicsek Model for user-defined variables, and then calculates corresponding order parameters and density plots. Within the GUI, the user can tune the control parameters and see the change in dynamics in real-time. The simulations will allow the user to make observations on the complex behavior and patterns based on geometric effects and reflecting boundary conditions. The GUI makes basic active matter simulations widely accessible and allows students and researchers to explore the complex dynamics. |
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G60.00071: Computational Electrochemistry of DNA and its Structural Units: Effect of Lithium Ryan Wong, Gakyung Kwon, Seung Soon Jang Through first-principles computational methods, the general electrochemistry of deoxyribose nucleic acid (DNA) was explored in connection to redox potential. The overarching objective was to uncover the redox capabilities of novel materials for potential electrochemical applications. Thus, in a systematic approach for its analysis, DNA was divided into three structural units of interest: the nitrogenous base, the deoxyribose sugar, and the phosphate group. By analyzing nucleobases, nucleosides, and nucleotides as separate species, the contributing electrochemical effects from each of these units were elucidated. Redox potentials were calculated from an alternative thermodynamic cycle, via density functional theory (DFT) modeling with PBE0/6-31G**+. Furthermore, given that solvents are often involved in electrochemical applications, it was necessary to consider the extent of their interactions with DNA, through PBF calculations. Results were compared among cases – with solvation applied at every level of optimization and calculation, and with solvation only applied via electrostatic potential fitting. From this study, new insights are offered on the relationship between structures and properties in DNA, promoting a fuller understanding of its electrochemistry for material design. |
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G60.00072: Synthesis and Purification of Silver Nanoparticles for Metal-Enhanced Fluorescence Briana Young, Joel Solomon, Bruce Wittmershaus Silver nanoparticles have many applications due to their surface plasmon resonance which makes them optically active to visible light. When organic dye molecules are close to their surface, the nanoparticles can increase the dye’s fluorescence quantum yield and photostability through metal enhanced fluorescence (MEF). To optimize the effects of MEF, the absorption spectrum of the nanoparticles must overlap the fluorescence spectrum of the dye. Prism-shaped particles enhance MEF through the strong electric fields at their points. To create them, silver perchlorate and sodium citrate were combined in the presence of sodium borohydride. This solution was then exposed to light from green, light-emitting diodes. The pH of the solution was varied to adjust the nanoprism’s size and optical properties. Following preparation, the nanoprisms were purified using centrifugation techniques to have a narrow absorbance peak at around 610 nm. By adjusting the pH and centrifugation parameters, a homogeneous sample of nanoprisms is isolated with the correct absorption wavelength to overlap with the dye’s fluorescence and maximize MEF. |
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G60.00073: PHYSICS EDUCATION
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G60.00074: Propagation of Gravity Waves through Periodic Media Leopoldo Diaz III, Luis Grave de Peralta The visualization of quantum mechanics tends to be difficult for new students and current quantum analogs do not do just in providing a clear picture of what quantum mechanics looks like. In this work, we have investigated the interaction of gravity waves and periodic media using a ripple tank. Through these interactions, we have found analogs for many of the introductory quantum mechanics cases, more specifically, the potential barrier, step potential, particle in a box, etc. We have shown through calculation that what we see in our ripple tank is analogous to what one would expect from a quantum mechanics scenario. |
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G60.00075: FABRICATION AND CHARACTERIZATION OF TIN FILMS FOR APPLICATIONS IN NANO-AND BIOLOGICAL SCIENCE AND ENGINEERING Meenakshi Singh, Svitlana Fialkova
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G60.00076: The Effects of Summer Camp on Participants’ Affective Views of Science Iliana De La Cruz, Micha Kilburn There exists a movement to draw more diverse groups of students to science, technology, engineering, and math (STEM) careers. While limited research on the effect of informal education on K-12 students’ views of science exists, recent data suggests children decide for or against STEM as early as grade school. This research quantitatively examines the effect a STEAM summer camp had on its participants’ affective views of science. Using pre-post surveys, the participants were asked to rate their interest in science, list career aspirations, and associate words they thought describe science or art. Researchers analyzed four years of these programmatic surveys for correlations between words associated with science, and age or gender. This summer, researchers also interviewed camp participants to better understand the reasoning behind word associations and to evaluate the survey instrument. Preliminary statistical analysis suggests camp affects participant word associating. Interview results highlighted points of confusion in participant survey instruction interpretation. |
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G60.00077: Taking Microcontrollers For a Spin: Revolutionizing Accessibility of Lab Activities Cody Jordan Introductory physics courses involve expensive and proprietary lab equipment not available after completion of the course, meaning that students are unable to make use of experimental techniques learned. Recent developments in the hobbyist electronics market have produced a wide range of components useable for accurate scientific measurement. We propose a method for conducting lab activities using inexpensive and open-source technologies, which will empower students in their own investigations and in formal lab settings. |
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G60.00078: Neutrosophic Methods in General Relativity Dmitri Rabounski, Florentin Smarandache, Larissa Borissova Applying the concepts of Neutrosophic Logic to the General Theory of Relativity to obtain a generalisation of Einstein’s four dimensional pseudo-Riemannian differentiable manifold in terms of Smarandache Geometry (Smarandache manifolds), by which new classes of relativistic particles and non-quantum teleportation are developed. Fundamental features of Neutrosophic Logic are its denial of the Law of Excluded Middle, and open (or estimated) levels of truth, falsity and indeterminancy. Both Neutrosophic Logic and Smarandache Geometry were proposed some years ago by F. Smarandache. The application of these purely mathematical theories to General Relativity reveals hitherto unknown possibilities for Einstein’s theory. The issue of how closely the new theoretical possibilities account for physical phenomena, and indeed the viability of the concept of a four-dimensional space-time continuum itself as a fundamental model of Nature, must of course be explored by experiment. |
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G60.00079: Cosmic Ray Cherenkov Detector Yessica Torrez Hernandez, Martin Reyes Jr. Cosmic rays are high energy particles that travel through space and shower Earth. Cherenkov radiation consists of electromagnetic radiation that is produced when remnants of secondary cosmic rays travel through earth’s atmosphere and surpass the speed of light in a material medium. Quantitative and qualitative analysis of cherenkov radiation can help determine the cosmic ray’s energy and speed. Our research project was to create simple and reliable Cherenkov detectors for use to outreach to high school STEM students. For this, we used two modified thermos bottles with distilled water as the medium to produce Cherenkov radiation. To observe the Cherenkov radiation from cosmic rays, two Photomultiplier detectors (PMT) were used and each was submerged in a thermos bottle and covered with light tight foils. Extensive evaluations were done for various placements of the detectors in both the vertical and the horizontal directions to obtain coincidence cosmic ray events. Results from our experiments indicated that the thermos detectors were detecting Cherenkov radiation produced by cosmic particles. |
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G60.00080: The nature of gravitational wave Han Quan Gravitational waves are radiation and the gravitational waves are a phenomenon that affects the relatively stable radiation network. Because of the rotation of the radiation source, the radiation is curved, and the bending radiation intersects and entangles to form a huge radiation net. The movement of the celestial bodies is the result of this huge radiation net. Often, this huge net is "very calm". Gravitational waves are hard to find because we exist in gravitational waves. Only when the huge celestial body abnormal movement, the radiation intensity, the scope of an instant increase, re-disturb the original quiet radiation network, this huge radiation network "abnormal" move, we can observe the "gravitational wave." Nevertheless, we can not observe the direct radiation after two black holes collided, observing anomalous changes in the cosmic gravitational wave net, such as gravitational lens and so on. Any celestial body has its scope of action, the scope of the celestial body should be the speed of light and celestial angular velocity ratio. If there is a gravitational effect between the two celestial bodies, then the radiation between the two celestial bodies must exist, the whole universe is a gravitational wave connection of the community. |
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G60.00081: The PLIC: Physics Lab Inventory of Critical Thinking Katherine Quinn, Cole Walsch, N Holmes The Physics Lab Inventory for Critical thinking (PLIC) is a new assessment under development and validation for physics lab courses. A great deal of time and money is spent on science lab courses, but there is little evidence evaluating whether they are providing good educational value. Labs also suffer from a lack of consensus on goals and on accepted assessment instruments. The PLIC aims to fill gap by assessing students' proficiency with critical thinking as related to making sense of data, variability, and models. Here we present the development and validation efforts thus far, and early data and findings. |
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G60.00082: Boosting Retention and Success in Introductory Physics Courses Through Math Assessment and Concurrent Remediation Miriam Simpson, V Glasser In introductory undergraduate physics courses, math is crucial to student success. Students come into these classes with diverse math backgrounds making it difficult to parse whether they are strugling with the physics concepts, the underlying math, or both. In order to establish a baseline for math skills, an assessment test was designed covering algebra, geometry, trigonometry, and calculus and given to students in the beginning of their first semester of introductory physics. The following year this same test was given, but then followed up with resources (videos and worksheets) to improve mathematical skills in areas of the test where they received low scores. The course content and instructor were kept the same. Both years 70-75% of the class recieved low scores in at least one subject. Students who were given additional math resources experienced better retention (16% dropped the course versus 26%) and the students who did not drop had better success (79% passed the course with a C or better versus 73%). This initial success has prompted the design of a more comprehensive study to identify how math weaknesses can be moderated with early interventions to increase success in these introductory courses. |
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G60.00083: Video Analysis of Argument and Explanation in an Introductory Classroom Eduardo Velazquez, James Laverty Recent efforts to transform science education have highlighted the importance of engaging students in scientific practices in order to develop their understanding of both the process and knowledge of science. This work focuses on identifying the scientific practices of Engaging in Argument from Evidence and Constructing Explanations in classroom video data. Our goal is to answer, “How can we identify when students are engaging in scientific practices in the classroom?” We are analyzing video recordings from an introductory physics class where students work on problems in groups of four for the entire two-hour class period. I have analyzed these videos for signs of students both engaging in argument and constructing explanations. This poster will discuss similarities and differences between these two practices and discuss how we can identify these practices in a valid and reliable way. This will allow us to investigate how students’ use these practices throughout a semester. |
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G60.00084: Angular velocities of particles Chen Xiao-Fan The expression of the angular velocity for a particle is given. The angular velocity of the particle is different from the angular velocity of a rigid body about a fixed point. |
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G60.00085: The value of out-of-class interactions: Attitudes vs. practice in introductory physics courses Justyna Zwolak From industry to government to academia, attracting and retaining science, technology, engineering, and mathematics majors is recognized as a key element of the 21st century knowledge economy. The ability to retain students seems to be intimately tied with understanding their immersion into the academic and social system of an institution. For instance, it has been noted that insufficient interactions with peers can lead to a low commitment to the university and, ultimately, affect one’s decision about whether to drop out. Since nearly half of first-time students who leave a university by the end of the freshman year never come back to college, the importance of understanding experiences in introductory courses as a means for improving students’ persistence is particularly pronounced. We investigate students’ experiences in an introductory physics courses, focusing on their self-reported perception of the values of and attitudes towards out-of-class collaborations. We find that, even though students consider the out-of-class collaborations to be important for success, it takes a relatively long time – basically an entire semester – before they start seeing benefits of collaborative learning and start translating their attitudes into practice. |
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G60.00086: PHYSICS OUTREACH AND ENGAGING THE PUBLIC
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G60.00087: The New SOCK: The Society of Physics Student’s Reimagined Outreach Program Jacob M. Robertson, Zakary Noel The Society of Physics Students (SPS) is a chapter-based professional association for undergraduate physics students. In addition to providing professional development for its members, SPS also encourages physics outreach on the chapter level. The major yearly outreach initiative, the Science Outreach Catalyst Kit (SOCK), has supplied SPS chapters with materials and instructions to perform outreach demonstrations in their communities since 2001. The SOCK development process also provides 1-2 SPS members the opportunity to develop science outreach and program development skills as summer interns. In 2017, the format of the SOCK was examined and reimagined to make more effective use of the budget and to expand the impact of the program on SPS chapters. As a result, 100 SOCKs were delivered in 2017 compared to approximately 25 in previous years. With the addition of online outreach resources, the remaining 712 of the total 812 SPS chapters can still benefit from the outreach program. Overall, the new program provides more outreach support to more members using approximately the same budget as previous years. |
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G60.00088: Qhord: A Detailed Dive into Music, Visualization, and Playing Quantum Mechanics Michael Seaman, Aaron Grisez, Justin Dressel The Qhord Project’s purpose is to promote playful curiosity about science (specifically among non-scientists), to foster science literacy in a wide demographic, and to advocate for the adoption of the STEAM (Science, Technology, Engineering, Arts, and Mathematics) model of education in the American education system and globally. Here, we present some of the finer mathematical details involved in our flagship development: a mobile application which lets users interact with an accurate quantum mechanical simulation through a musical interface. We explore the issues surrounding the inaccessibility to quantum physics and offer viable solutions to generate more public interaction with science experts. |
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G60.00089: 21st Century Challenges: Developing Sustainable Energy & Facing the Climate Change Irina Bariakhtar, Victor Bariakhtar, Ya. Bykovsky It is well known that the industrial societies of modern days require a significant amount of energy to support their vitality. Therefore, a question of usage and optimal proportion between the traditional energy sources and new sustainable energy sources comes as an important issue and challenge to both scientists and policymakers. In this presentation, the authors suggest their views, analytical calculations and scientific predictions as to the usage of atomic energy, solar, thermal and wind energy as the sustainable and efficient energy sources of modern human society. |
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G60.00090: Flying with NASA Leandro Oka, Itália Barbosa, Paulo Gomes The internet allows high quality and free scientific content to be available anywhere on the planet. Whether it's propaganda for future missions or reporting results of already accomplished ones, the american space agency NASA and the european one ESA make and release several didactic videos about space exploration and astrophysics. The videos aim the general public and have detailed and well crafted animations about the physical concepts studied on the missions. The outreach project called "Flying with NASA" aims to bring the debate of these topics to the high schools of the small city Jataí in central Brazil through the presentation of the NASA videos (Youtube channels such as Hubble Space Telescope, NASA Gorddard, NASA Jet Propulsion Laboratory, NASA Spitzer among others). Subtitles translated into Portuguese by users and also by ourselves allow students to overcome the language barrier. Several topics were addressed such as solar system, space telescopes, Sun, Jupter, Saturn and stars. The most successful topics were time travel, black hole, wormhole, universe size, and existence of life outside Earth. The visual appeal of videos is crucial in attracting the students' interest. |
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G60.00091: Future Faces of Physics: Palomar Planetarium Outreach Event Josefa Gregorio, Jesus Perez, Edwin Robles, Justin Perron With support from the 2017 Society of Physics Students Future Faces of Physics award CSUSM students organized an outreach event for students at San Marcos Middle School which has a large population of minority students underrepresented in the STEM fields. The event involved a field trip to a planetarium and included various activities and discussions between the middle school students and CSUSM undergraduates. Pre and post surveys were administered in an attempt to gage efficacy of the outreach. This talk will describe the details of the activity, the results of the surveys, and how future iterations may be adapted in hopes of improving the events impact. |
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G60.00092: Why the History of Physics Matters Lexxi Reddington The Niels Bohr Library & Archives boasts a robust archival collection about the history of physics. As an SPS Intern for the Library, I was tasked with highlighting the human story behind scientific discoveries through a physical and online, museum-style exhibit that utilizes the Library’s documents and images. In contemplating a theme for the exhibit, I determined that questioning why the history of physics matters in the first place would be important. The intent was to engage people outside of the field of history, especially other physics students, with the resources that the Library provides. Initiating this engagement necessitated an explanation of the relevance of the history of physics to physics. History is often disregarded as extraneous or inconsequential to scientific work. But, history is inherently connected to all facets of scientific inquiry because it documents all attempted, achieved, and anticipated discoveries. Drudging up the history textbooks may seem like an absurd way to advance science, but because history involves a collection of ideas, theories, and equations that becomes the foundation for future improvements, understanding the history of physics is undoubtedly indispensable. |
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G60.00093: PHYSICS OF CLIMATE
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G60.00094: In-Situ Measurement of Forrest Soil Gases using Quadrupole Mass Spectrometry Tim Porter, T. Dillingham The net effect of forest soils on the overall atmospheric concentration of methane and carbon dioxide is complex and relies upon many different factors. The flux of these gases from the soils may vary significantly depending upon temperature, water content, soil compaction, soil composition, root structure within the soil, decaying forest components within the soil, and other factors. We have developed and tested a portable, battery powered quadrupole mass spectrometer that allows for in-situ, real time measurement of the concentration of gases in soils. This instrument allows for rapid, simultaneous quantification of methane, carbon dioxide, water vapor and other gases in the near surface region of the soils. Here, we have measured the concentrations of methane and carbon dioxide in the soils of the Coconino National Forest, comparing gas levels in regions of the forest that have been mechanically thinned vs. nearby regions that have been undisturbed. |
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G60.00095: Tropical Cyclone Effects on Seasonal Climatology in the Gulf and the Atlantic Ocean Alex Burnette, Todd Emmenegger, Jose Rial The hurricane season of 2017 experienced long-lived, destructive, tropical cyclones (TCs). Harvey, Irma, and Maria developed successively, registering at least at Category 4 status before making landfall. Harvey resulted in 80 deaths and extreme flooding in the Houston, Texas area. Irma followed shortly after in the Florida Keys, resulting in 132 deaths, and was the second most intense cyclone in the world in 2017 behind Hurricane Maria. Maria hit Dominica and Puerto Rico, resulting in 93 deaths, and is the worst natural disaster recorded in Dominica to date (modis.gsfc.nasa.gov). This study aims to investigate the effects of tropical cyclones on seasonal climatology in the Gulf and bordering regions of the Atlantic Ocean using NOAA’s HURDAT 2 record for TCs since 1981. Previous studies explore the ocean’s response to the passing of a TC and conclude that sea surface temperature experiences a downward spike before returning to its climatology after a period of around 26 days (Price 1981). We revisit studies of ocean response and the variability of other climactic factors known to contribute to a TC’s intensification, and we examine whether a TC’s passing makes conditions more favorable for another TC to develop in the same region and season. |
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G60.00096: Studies of stationary waves controlling monsoon precipitation in climate change - using North American monsoon during Last Galcial Maximum Hung-I Lee, juan lora, jonathan mitchell, Aradhna Tripati Understanding the response of monsoon precipitation distributions to different climate states can serve to test climate model simulations, but many challenges remain owing to multiple controlling factors. Here, we quantitatively compare a synthesis of pollen proxies of precipitation during Last Glacial Maximum (LGM, 21ka) precipitation over North America to constrain the Paleoclimate Intercomparison Model Project (PMIP3) ensemble. In model simulations that compare favorably with proxy synthesis, we find a strong correlation between monsoon precipitation and meridional wind anomaly, suggesting the patterns are mainly governed by extra-tropical forcing. The major perturbations of meridional wind anomaly under LGM consist of topographic forcing due to rising elevation from the Laurentide ice sheets and thermodynamic forcing due to alteration of the mean state from albedo change. Weak westerlies are generated by models with favorable comparison to the proxy synthesis. We are testing if the alteration of westerlies contributes to Rossby waves and monsoon precipitation distributions in North America during LGM. |
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G60.00097: Estimating Carbon Dioxide Emissions from Cities using In-situ and Remote Measurements on Low Cost Drones Siona Prasad Carbon dioxide (CO2) emissions, especially from large cities have resulted in the build-up of greenhouse gas concentrations. Existing sensor technology is too expensive for large-scale use and cannot distinguish between anthropogenic and biogenic emissions. Current platforms for measurement are limited in height and stability. In this paper, I develop a low-cost in-situ sensor for direct CO2 measurements and a spectral imaging system to remotely monitor vegetation phenology. The sensor and camera were installed on a drone for greater mobility and mathematical models used collected data to estimate emission inventories. The low-cost sensor compared favorably with state-of-the-art instruments (correlation factor = 0.99) and exhibited expected annual, seasonal and diurnal trends. The normalized difference vegetation index was computed from spectral data, and correlated with plant transpiration and carbon exchange. The predicted CO2 emission inventory for Washington DC showed a large contribution from the transportation sector. In summary, I demonstrate a methodology to measure and monitor city-wide CO2 emissions by combining low-cost in-situ measurements, multispectral imaging, small drone technology and puff modeling. |
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G60.00098: GENERAL
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G60.00099: Generation of Gravitational Waves by the Spin, Orbital Angular Momentum and Interaction of Fundamental Particles, or Gravitational Waves Hypothesis Hassan Gholibeigian Gravity like magnetism is a quantum mechanics phenomenon. Different mechanical motions of the fundamental particles like spin, orbital angular momentum, and interaction between these two are the origin of the waves (gravitational and magnetic waves (GMW)) in quantum area. The waves which are arising from these motions interact with each other in processes and enhanced their strength. Physicists can detect magnetic waves; however, they are not able to detect gravitational waves in quantum level yet, due to its weakness. In black hole, the orbital angular momentum and interaction between particles involving local and global large scale convection systems, become highly more. Therefore, radiated GMW become highly more. An observable factor is; observation of the binary neutron star merger GW170817 by LIGO, Virgo, Fermi, and Integral indicate that the association of gamma-ray and gravitational-wave signals are the progenitors of one class of gamma-ray bursts. It implies that the origin of gravitational and magnetic waves may be from fundamental particles. In other words, the gravitational waves are continually generating by fundamental particles. Moreover, in Big Bang, GMW and fundamental particles may be created together. In this viewpoint, theory of everything may be proven. |
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G60.00100: Gravitational Lensing by Dark Matter Halos Sergio Grijalva-Castillo, Carlos Calcaneo-Roldan In the last two years, with the confirmation of gravitational waves, its clear that a new window in the area of professional astronomy has opened; in particular "gravitational wave astronomy". In this work we study the magnification effects of the amplitude of the gravitational wave due to a spherically symmetric distribution of mass between the source and the observer. The effect on the wave amplitude is via the magnification function, a procedure developed originally by T.T. Nakamura and S. Deguchi (PTP Supp 133, 137. 1999) via de deflection integral formula. We concentrate our efforts particularly on studying the effects of realistic dark matter haloes on the gravitational wave, in the hope that the magnification effect may be used to distinguish between different dark matter halo density profiles. |
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G60.00101: GOLDBACH-CONJECTURE-(IN NUMBER(#)-THEORY) IS ANTI-COOPER-PAIRING(IN NON-SC) GapFUL Fermion/PAIR-BREAKING SC-TO-NORMAL PHASE-TRANSITION CRITICAL-PHENOMENON: Primes N-BEC-Factorization/DEncryption-Cyber-THREATS(IBM/BlockChain) Are MANDATORY!!! E. Carl-Ludwig Siegel, Gian-Carlo Rota, Jules Henri Poincare, Frederic Young UNreasonable Effectiveness of Physics in Maths: Watkins [www.mathewwatkins.net]-Schulmeyer/Hutchinson[arXiv Physics of RH]-Wolf[arXiv.Will a Physicist Prove RH?]-Derbyshire[Prime Obsession(04)-Sabbagh[Prime-Numbers/RH(06)]-Siegel[APS Nuclear-Div. Mtg(10): Google: Nuclear-Physics in Number-Theory in Nuclear Physics; AMS Joint-Mtg, SD(02)=3 papers!; (18)=several papers!!!; SEVERAL SIAM ConfS. (18)-… POSITING(NON-FACTORABLE/FACTOR-LESS) PRIMES = (ATTRACTING) BOSONS VS. (FACTORABLE) COMPOSITES = (REPELLING) FERMIONS WITH Holthaus[(04)] FACTORING NUMBERS BY BEC, in ostensibly “pure”-maths NUMBER-theory GOLDBACH-(1732)-CONJECTURE: “EVERY EVEN-COMPOSITE-NUMBER>2 IS SUM OF TWO-PRIMES” is shown analogous to ANTI-COOPER DE-PAIRING/ANTI-BCS-THEORY/ANTI-SC, ie a (COOPER-DE-PAIRING) BCS-SC-TO-(NON-COOPER-PAIR-ING) NORMAL/NON-SC PHASE-TRANSITION CRIT8CAL -PHENOMENON! Critical-ExponentS?/Scaling-RelationS? Renormalization-group analytics of ostensibly “pure” maths number-theory GOLDBACH-conjecture as a (Cooper-pairing)-BCS-SC-T0-(NON-COOPER-DEpairing)NON-BCS/NORMAL phase-transition critical-phenomenon is STRONGLY indicated! ApplicationS: encryption Cyber-“security” RSA-“secure”-encryption protocol |
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G60.00102: RIEMANN-Hypothesis STATISTICAL and SOLID-STATE CRYSTAL-LATTICE PHYSICS Floquet-Theory-Bloch-Brllouin OBSERVATIONS/ . . ./ INSPIRATIONS as to a COLLABORATIVE Eventual Formerly Hoped For “Pure”-Mathematics” Proof “BOSON-ICS”!!!; Renormalization-(SEMI)-Group Analytics of (Analytic/Computational)-Number-(#)- E. Carl-Ludwig Siegel, Gian-Carlo Rota, Jules Henri Poincare, Frederic Young RIEMANN-Hypothesis STATISTICAL and SOLID-STATE PHYSICS FLOQUET-Theory-Bloch-Brillouin[“Wave-Propagation in Periodic-Structures” (46); (31); (22) |
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G60.00103: RIEMANN-Hypothesis STATISTICAL and SOLID-STATE CRYSTAL-LATTICE PHYSICS Floquet-Theory-Bloch-Brllouin OBSERVATIONS/ . . ./ INSPIRATIONS as to a COLLABORATIVE Eventual Formerly Hoped For “Pure”-Mathematics” Proof “BOSON-ICS”!!!; Renormalization-(SEMI)-Group Analytics of (Analytic/Computational)-Number-(#)- E. Carl-Ludwig Siegel, Frederic Young, Gian-Carlo Rota, B. Riemann
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G60.00104: PUBLIC POLICY
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G60.00105: Research Integrity and the Responsible Conduct of Research Aaron Manka
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G60.00106: INTERNATIONAL ISSUES
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G60.00107: Updates on the African Synchrotron Light Source (AfLS) Project Tabbetha Dobbins, Sekazi Mtingwa, Ahmadou Wague, Simon Connell, Brian Masara, Tshepo Ntsoane, Lawrence Norris, Herman Winick, Kenneth Evans-Lutterodt, Tarek Hussein, Feene Maresha, Krystle McLaughlin, Philip Oladijo, Esna du Plessis, Romain Murenzi, Kennedy Reed, Francesco Sette, Sverker Werin, Jonathan Dorfan, Mohammad Yousef Africa is the only habitable continent without a synchrotron light source. A full steering committee was elected at the African Light Source (AfLS) conference on November 16-20, 2015 at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The conference brought together African scientists, policy makers, and stakeholders to discuss a synchrotron light source in Africa. Firm outcomes of the Conference were a set of resolutions and a roadmap. Additionally, a collaborative proposal to promote Advanced Light Sources and crystallographic sciences in targeted regions of the world was submitted by the International Union of Pure and Applied Physics (IUPAP) and the International Union of Crystallography (IUCr) to the International Council for Science (ICSU). www.africanlightsource.org. |
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G60.00108: MAGNETISM
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G60.00109: Hole Binding in the One-Dimensional Dimerized Heisenberg Model with Next-Nearest-Neighbor Interactions Jay Mancini, Samuel Bowen, Vassilios Fessatidis Here we wish to study the 1D dimerized Heisenberg model given by H=∑k J1[1-(-1)kδ]{S(+)k+1S(–)k+2S(z)k+1S(z)k}+∑k J2{S(+)k+2S(–)k+2S(z)k+2S(z)k}, where S(±) are the usual spin ½ stepping operators and δ is the dimerization parameter. In particular, we shall use a Lanczos formulation to study the binding energy of two holes, ΕB = Ε0 wo holes) + Ε0 (no holes) – 2Ε0 (one hole), where we have varied the ground-state configuration so that we may evaluate ΕB as a function of hole separation. |
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G60.00110: The Possible Mechanism of the Change of Carrier Types in SrRuO3 Films SSU-TING LIN, GOPESHWAR DWIVEDI, PO-YU CHEN, Chou Hsiung, Shih-Jye Sun SrRuO3 is widely used as a conduction layer for multilayer system, which exhibits a ferromagnetic transition around 165K. The SRO films were grown by a standard PLD system with a thickness of 180nm. The X-ray and Neutron scattering show the quality of the films is as good as a single crystal. The transport and magnetic measurement indicates a parallel-ferromagnetism transition at 155K. Hall measurements shows a clear hysteresis loops at low field region, the anomalous Hall effect, when the temperature is lower than the TC. At high field region, corresponding to a normal Hall effect, the conduction carriers is found to be electron-like below TC and hole-like above TC. Since the Hall coefficients changes sign from negative to positive around TC indicating the spin-split coupling strongly affects the local band structure. The split bands is simulated as a two-band model to describe the Hall measurement results. Two bands changes while magnetic coupling is introduced at low temperature. |
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G60.00111: Hole Binding in a One-Dimensional Long-Range Spin ½ Interaction System Jay Mancini, Samuel Bowen, Vassilios Fessatidis Using a Lanczos tridiagonal scheme to generate our basis, we study the novel spin chain Hamiltonian (expected to be in the same universality class as an XY Heisenberg system) given by H = ∑N−1j=1 ∑Nk=1 j(−1−p) [S(+)k+j S(−)k + S(−)k+j S(+)k + λ (S(z)k+j S(z)k + S(z)k S(z)k+j)]. By varying the initial (trial) state, we then study the hole binding energy, EB = E0 (two holes) + E0 (no holes) − 2E0 (one hole), as a function of hole separation, anisotropy parameter λ as well as the parameter p. |
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G60.00112: Robustness of low-field anomalous magnetism in kagome Co3Sn2S2 Po-Jung Sun, Hung-Cheng Wu, D Chandrasekhar Kakarla, Hung-Duen Yang Kagome Co3Sn2S2 polycrystalline samples with different nominal mixtures of starting materials have been synthesized using solid-state-reaction method and characterized by X-ray diffraction (XRD) and electron probe microanalyzer (EPMA). AC susceptibility (χ'ac) with fine tuning temperature and magnetic field dependence were measured. The H-T phase diagram of Co3Sn2S2 derived from χ'ac –T and dχ'ac /dT–T with various magnetic fields is presented. The phase diagram including so-called A phase with 0 Oe ≦ H ≦ 600 Oe and 132 K ≦ T ≦ 173 K, which had been reported earlier. More interestingly, within 150 Oe ≦ H ≦ 300 Oe and 132 K ≦ T ≦ 160 K, a new feature so-called phase is found. These and phases are negligibly dependent on S-rich doping samples Co3Sn2S2+x (0 ≦ x ≦ 0.34) indicating the robust of anomalous magnetism in low magnetic field. The possible origins for the novel observations in kagome Co3Sn2S2 will be discussed. |
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G60.00113: Curie Temperature Dependence on Chemical Ordering in FePt and CoPt Nanoparticle Frank Abel, Onur Tosun, Vasileios tzitzios, Ralph Skomski, David Sellmyer, George Hadjipanayis Current ultra high density recording media utilize the high magnetocrystalline anisotropy of L10 FePt allowing for ferromagnetism down to 3 nm. To use these materials, the media must be heated close to the Curie temperature for a small applied field to switch the particles or grains [1]. The technological requirements for the realization of heat assisted magnetic recording requires a precise understanding of the temperature dependent magnetic properties of FePt and CoPt nanomaterials. |
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G60.00114: Synthesis of Chiral Three-Dimensionally Ordered Mesoporous Superconducting Niobium Nitride Gyroids using Block Copolymer Self-Assembly Peter Beaucage, Sol Gruner, Ulrich Wiesner Superconductors with three-dimensional (3D) mesoscale order and porosity are expected to have properties very different from their bulk counterparts. For example, flux pinning in mesoscale lattices may result in enhanced upper critical fields or novel angle-dependent behavior, and a chiral mesostructure might allow nonlinear magnetoelectric couplings or other properties. The exploration of these properties has been limited by a lack of versatile, tunable synthetic approaches to such 3D mesoscale ordered superconductors. We report the synthesis of gyroidal mesoporous niobium nitride from block copolymer self-assembly derived mesoporous niobium oxide with subsequent high temperature treatment in flowing ammonia gas. The resulting materials have a Tc of about 7.8 K and a mesoscale lattice with the I4132 (alternating gyroid) structure with lattice spacings between 27 and 36 nm. Recent efforts to improve the superconducting properties of these materials and to expand the accessible range of length scales and structures will be discussed. We expect block copolymer-inorganic hybrid co-assembly will prove to be a versatile platform for exploration of the impacts of mesoscale order and porosity on the magnetic properties of superconductors. |
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G60.00115: Deterministic Magnetization Rotation in Nano Magnetoelastic Rings Abdon Sepulveda, Cai Chen, Greg Carman, Jin-Zhao Hu, Kevin Landry Realizing deterministic magnetization rotation remains a challenging problem in multiferroic system. This work examines conditions required for deterministic magnetization rotation in a Nickel ring with dimensions: inner radius 350 nm, outer radius 500 nm. The ring is on top a piezoelectric substrate where electrodes are placed to induce in-plane stresses. The study determines how strains must be applied to have magnetization rotation at const. angular speed. The in-plane flexibility of rings makes it difficult to induce the correct strain profile for rotation. Since the ring is made of Ni which is negative magnetostrictive, we determine the attraction area of influence (i.e. how far can the magnetization rotates from induced strain location) for each electrode as a function of applied voltage, electrode config. and rigidity of inner core. Parametric studies determine speed of rotation (when it does) and the input energy required. These results are then used to determine optimal electrode geometry and the way in which strains should be applied. This work will provide practical framework for the design of actuation systems for the control of the magnetization in rings. Multiple applications in the field of nano-motors are envisioned, for example cell manipulation. |
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G60.00116: Novel Exchange-coupled Core / Shell Nanoparticles for Advanced Magnetic Hyperthermia Caroline Collins, Joshua Robles, Raja Das, Manh-Huong Phan, Hariharan Srikanth In the search for novel non-harmful cancer treatments, magnetic nanoparticles (MNPs) have shown potential to engage in localized destruction of cancer cells via magnetic hyperthermia—a process that minimizes damage to the patient. It has been found that as the size of the MNP decreases, the heating efficiency drastically decreases. Recently, however, a large improvement in heating efficiency has been reported in exchange-coupling of MNPs between a soft and a hard magnetic material. In this study, we optimized the heating efficiency of exchange-coupled MNPs composed of a soft magnetic core (Fe3O4) and a hard magnetic shell (CoFe2O4) by tuning both the shape of the nanoparticles and their concentration in solution. The MNPs show high magnetization (~80 emu/g) and superparamagnetic-like behavior at room temperature. We compare the specific absorption rate (SAR) for each set of MNPs and correlate the results to shape distribution and concentration in solution. This study shows that exchange-coupled MNPs for magnetic hyperthermia are promising as route for non-harmful cancer treatment. A new approach for controlling the inductive heat for cancer treatment using a mixture of spheres and cubes is proposed. |
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G60.00117: Modeling Static and Dynamic Properties of Magnetic Nanowire Arrays using MuMax3 Robert Eimerl, Karl Muster, Ranko Heindl We simulated first order reversal curves (FORC) and ferromagnetic resonance (FMR) in arrays of magnetic nanowires using open-source micromagnetic simulation program MuMax3 running on a graphics processing unit (GPU). Nanowires in our work are either made of a single element (eg. Ni, Co), alloys (eg. CoFe, NiFe), or multilayers (eg. Co/Ni, Cu/Ni). Nanowire arrays were electrodeposited into anodic alumina templates. FORCs were measured using vibrating sample magnetometry, and FMR was measured using the broadband ferromagnetic resonance method. We compare the simulated with the experimental results. Our interest is to study the relationship between static (FORC) and dynamic (FMR) properties as well as their relationship to crystalline properties, texture, defects, and composition of nanowires, which we both simulate and measure using X-ray diffractometry. |
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G60.00118: Effect of particle size on Curie temperature and coercivity of Gadolinium silicide (Gd5Si4) Shivakumar Hunagund, Ahmed El-Gendy, Shalabh Gupta, Vitalij Pecharsky, Shane Harstad, R. L. Hadimani Nanoparticles (NP) exhibit different properties from their parent bulk materials due to finite size & surface effects. In this study, size dependent magnetic properties of Gadolinium Silicide (Gd5Si4) NP from ball-milled ingot are investigated. NP were size separated into 8 fractions using time sensitive sedimentation in an applied dc magnetic field. SEM image analysis shows average NP sizes of 700nm,615nm,560nm,470nm,342nm,223nm,84nm and 82nm for the 8 corresponding fractions. XRD analysis indicates that Gd5Si4 is the major phase and Gd5Si3 is the minor phase present in all fractions. VSM measurements reveal that as the NP sizes decreases, the transition temperature (Tc) of Gd5Si4 is reduced from 316K to 312K and to 310K, while the ordering of the minor phase is independent of the NP sizes with stagnant Tc at 110K. The M-H curves at 300K exhibits ferromagnetic behavior descending to paramagnetic across fractions. Coercivity (Hc) obtained from hysteresis plots show that Hc increases with decrease in NP size across fractions until it reaches critical single-domain size & then decreases toward zero where it becomes superparamagnetic. |
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G60.00119: Theoretical Study of the Fe(btr)2(NCS)2 Spin-Crossover Complex with Reparametrized Density Functionals Saho Kajikawa, Azusa Muraoka Under various constraints, such as temperature or pressure variations, spin crossover (SCO) solids can be switched from the low-spin (LS) state, diamagnetic S = 0 to the high-spin (HS) state, paramagnetic S = 2 conversely. In many cases, the elastic interactions between the SCO units are strong enough to induce a hysteresis at the thermal spin transition which occurs as a first-order phase transition. Such “switchable” molecular solids are promising in terms of optical data storage. In this study, we explore the functional for density functional theory (DFT) calculations that reasonably reproduce the first-order transition, LS/HS energy, electronic state and IR spectral assignment of Fe(II) SCO compounds [Fe(btr)2(NCS)2]. A suitable functional was selected by comparing the experimental value of the LS/HS enthalpy difference. The configuration coordinate diagram of LS/HS shows that the LS state has higher stability than the HS state. It was found that the average Fe - ligand distance in the HS state is 0.22 Å longer than the LS state, and the structure is greatly changed. Moreover, the vibrational intensity of C ≡ N group and Fe are greatly different depending on the spin state and on the intramolecular interactions for the structure configuration around Fe. |
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G60.00120: New Nuclear Radiation Detector Made by Core-Shell Magnetic Nanoparticles Lokendra Khanal, You Qiang Iron/iron-oxide core-shell nanoparticles (NPs) have been found potential nanomaterials for radiation sensing and monitoring in the nuclear radiation. It has been shown extremely sensitive behavior under Si2+ ions irradiation even at very low dose of ion fluxes. Since heavy ions behave like neutron in terms of the radiation effect and defect creation, the core-shell NPs have been proposed for highly sensitive neutron radiation detection at high temperature in the core of the nuclear reactor. In order to study the high temperature structural and morphological behavior of the core-shell NPs, annealing tests have been performed up to 800 0C in vacuum, oxygen and argon environment. The ~18 nm size of the as prepared NPs increases slowly on annealing up to 500 0C in all three environments but increases abruptly in argon and oxygen environment but slow in vacuum when heated to 800 0C. The x-ray diffraction studies have shown that the iron core remains in the core-shell NPs only when they are annealed in the vacuum environment, which is important for the high temperature neutron detection in the core of nuclear reactor. The size distribution, size growth mechanism and phase transformation of the NPs will be discussed in this presentation. |
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G60.00121: First Principles Model of Magnetic Nanoparticle Behavior in Various Fluid Environments Pulkit Malik, Ben Shapiro Magnetic nanoparticles (MNP’s) have garnered lots of interest in various bioengineering fields for applications such as targeted drug delivery and cell manipulation. Characterization of MNP behavior in magnetic fields is an important step towards realizing these applications. This model will allow particle design to be optimized and rapidly prototyped as part of a magnetic system. The MNP’s considered in this model are spheres comprised of magnetic cores encapsulated by a non-magnetic material. In this model, four forces are considered to be acting on each particle; the force due to a magnetic gradient, dipole-dipole interactions, steric hindrance, and viscous drag. The model is a quasi-steady-state model, since the particles are assumed to reach steady-state velocity very quickly due to their small mass, meaning acceleration terms are set to zero. The model was verified with velocity and chaining length comparisons, as a reference to chaining behaviors, to PLGA nanoparticles with magnetic cores. An example of particle design in an inhomogeneous fluid environment is shown to demonstrate the ability to use the model to influence particle design. |
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G60.00122: Magnetic and Magnetotransport properties of pulsed laser deposited Fe90Ta10 thin films Surabhi Shaji, Nikhil Reddy Mucha, A.K Majumdar, Dhananjay Kumar 3d/4d structures involving heavy transition elements have long been known to possess good permanent magnetic properties because of their ability to induce large anisotropy in structures such as L10 magnets. Reports suggest that low content of Tantalum (W) has the potential to induce large magneto crystalline anisotropy and increase magnetization in iron as a result of large spin-orbit coupling of 4d elements which can lead to strong 3d/4d hybridization. Fe90Ta10 thin films exhibited enhanced coercivities (259.76 Oe) and saturation magnetization (425 emu/cm3). The results have shown that the easy magnetization direction was in-plane which was structurally determined by xrd to be (111).The anisotropy energy was calculated, which is larger than many known ferromagnetic materials. We have also observed Extra-ordinary Hall Effect in Fe-Ta films which establishes the scaling behavior of the extraordinary Hall constant, Rs. An involved analysis of high-resolution Hall (B, T) data recorded at temperature from 5 to 300 K shows that the scaling exponent, n in Rs ~ ρn, where ρ is the Ohmic resistivity, is ~ 1.1 ± 0.1. Theoretically, for homogeneous ferromagnets, n = 1 corresponds to Smit classical asymmetric scattering while n = 2 is attributed to the quantum mechanical side-jump scattering |
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G60.00123: Nano-Co synthesized by sol-gel progress with acrylamide and pea (pisum sativum) and lucerne (medicago sativa): magnetic and structural properties. Ricardo Gerardo Torres, Elizabeth Chavira, Magali Ugalde, Adriana Nereida Avendaño Gavira, Jesus Arenas, Guadalupe Zavala, Francisco Espinosa, Adriana Tejeda, Carlos Flores, Karla Eriseth Reyes-Morales, Jorge Barreto, Omar Novelo, Josué Romero-Ibarra, Martha Teresita Ochoa Cobalt nano-materials are widely used in the manufacture of biomedical, medical sensors, and contrasting agents in magnetic resonance imaging procedures. Also, its electromagnetic wave shielding properties makes the compound ideal for use in manufacture of cell phones. Co3O4 (STREM CHEMICALS) was used, X-ray powder diffraction, (PDF 43-1003) and 3% of several iron oxides impurities. Co3O4 was diluted with HCl and HNO3 at 321 K, under constant magnetic stirring, gets CoCl2 salt. With sol-gel (microwave-assisted) we added monomer acrylamide, crosslinker agent N, N'-methylenebisacrylamide and polymerization accelerator agent α, α'-azodiisobutyramidine dihydrochloride, 3 s to obtain the gel. We detect the oxidation changes of the Co in each synthesis stage process done. The pea (pisum sativum) and lucerne (medicago sativa) was grown-up in distilled water with Co3O4. Thermogravimetric analysis determines gel’s stages of degradation. In order to remove the organic compounds a thermal treatment at 873 K, was given to the gel. By Atomic Force Microscopy saw the topography of Co and crystals size (50- 120 nm). Measure of magnetic properties changes with the crystal sizes. HRTEM we visualised the Co in pea, lucerne and the shape of the nano-crystals. |
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G60.00124: Single crystal growth and magnetoelectric effect of Co4Nb2O9 Shixun Cao, Yiming Cao, Jincang Zhang, Wei Ren Multiferroics have attracted a lot of attention as they exhibit coexistence of two or more switchable states such as electric polarization, magnetization or strain rendering them very interesting for both their intriguing fundamental physics and promising applications. In the route towards materials having strong magnetoelectric (ME) responses, Co4Nb2O9 (CNO) is very attractive. Both the magnetically-induced electric polarization and the control of magnetization with an electric field were observed in polycrystalline CNO. In this work, we first grow successfully single crystal of CNO samples by using optical floating zone technique, and find that the spin flop occurred along a axis rather than c axis. Furthermore, detailed ME measurements reveal a nonlinear ME effect, with linear and quadratic coefficients. A pronounced response was observed under a small cooling magnetic field which cannot even cause the spin flop. We also found that the magnetization of every axis responds to electric field applied along a-axis, but fail to do so when the electric field is applied c-axis. |
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G60.00125: Magnetic properties of stoichiometric and defective Co9S8 Marco Fronzi, Sherif Tawfik, Mike Ford In this paper, we present a detailed study of the stoichiometric and reduced magnetic properties of Co9S8 pentlandite, based on density functional theory. We analyze both its geometry and electronic properties and show that only by the inclusion of the Hubbard term it is possible to correctly describe d−d splitting, which is necessary to accurately characterize the Co9S8 spin configuration and its antiferromagnetic nature. We also analyze the effect of sulphur vacancies and predict the formation of ferromagnetic clusters that give local ferromagnetic character to non-stoichiometric Co9S8, which may explain the contradictory experimental results reported in the literature. |
(Author Not Attending)
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G60.00126: Effective spin-orbital model for correlated 2DEGs in (111) oxide heterostructures Gideon Wachtel, Nazim Boudjada, Arun Paramekanti Recent experiments have begun exploring the physics of 2D electron gases in (111) oxide heterostructures. Motivated by understanding the nature of broken symmetry states which could be potentially realized in such 2DEGs, we have studied correlation effects and the impact of thermal fluctuations by studying an effective spin-orbital Hamiltonian. The form of the Hamiltonian is dictated by symmetry and its parameters are obtained by a detailed comparison with a Hartree-Fock mean field theory. A Monte Carlo study of this effective model shows that the system transitions from a high temperature paramagnetic phase into a low temperature nematic phase with ferro-orbital order. We discuss such ordering tendencies in light of recent experiments on such (111) 2DEGs which appear to find broken rotational symmetry. |
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G60.00127: magnetocaloric effect and its modulation by electric field in La0.325Pr0.3Ca0.375MnO3 film grown on PMN-PT Kaiming Qiao, Hongrui Zhang, Fengxia Hu, Jirong Sun, Baogen Shen We have investigated the magnetocaloric effect(MCE) and its modulation by electric field in La0.325Pr0.3Ca0.375MnO3 (LPCMO) films epitaxially grown on (011)-oriented PMN-PT substrates. As a typical perovskite manganite with phase separation, the LPCMO bulk shows a considerable MCE, but the MCE of the LPCMO films have never been investigated. We found that the LPCMO films exhibit an inverse magnetic entropy change below 25K and an normal magnetic entropy change above 25K over a wide temperature range. The evaluated refrigeration capacity of 0-5T in the present film is about 443J/kg, which is larger than that of other films such as Ni-Mn-Sn film. A modulation of magnetization by electric field has been observed in the temeprature dependent and magnetic field dependent curves. As a result, enhanced magnetic entropy change and refrigeration capacity by about 4% under an electric field of 6 kV/cm has been demonstrated. |
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G60.00128: A strain-addressed high temperature perovskite ferromagnetic insulator Xiaofang Zhai, Dechao Meng, Hongli Guo, Chao Ma, Jinghua Guo, Jin Zhao, Yalin Lu Ferromagnetic insulators with a high Curie temperature and a high symmetry structure are critical for potentially being well integrated with common single crystalline oxide films or substrates. The commonly used ferromagnetic insulators are mostly with low symmetry structures associated with poor growth integrity. The only few investigated high symmetry materials either have very low Curie temperatures (≦16 K), or require chemical doping into an antiferromagnetic matrix. Here we demonstrated a tensile-strain addressed LaCoO3 thin film to be the non-doped perovskite ferromagnetic insulator, yet with a remarkable transition temperature as high as 90 K. Both experiments and the first-principles calculation demonstrated that the tensile strain induced the intrinsically not existed ferromagnetism. The ferromagnetism reaches the strongest within a nearly stoichiometric structure, and disappears when the introduced Co2+ defect concentration reaches to a critical amount. Significance of the research includes the availability of a successful elevation of the transition over the liquid-nitrogen temperature and a high integration potential in the large area device fabrication. |
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G60.00129: Magnetic Two-Dimensional Electron Gas at A Manganite- Buffered LaAlO3/SrTiO3 Interface Hongrui Zhang, Rui Li, Kaiming Qiao, Fengxia Hu, Baogen Shen, Jirong Sun Magnetic two-dimensional electron gas (2DEG) at the LaAlO3/La7/8Sr1/8MnO3(2uc)/SrTiO3 interface has been fabricated by introducing tiny amounts of magnetic ions into the interfacial layer of SrTiO3. Experiments show that the ferromagnetic order and carrier mobility of the 2DEG have been simultaneously enhanced. The temperature range for the 2DEG to spin-polarized is six-fold increased and the anomalous Hall resistance, which is also opposite in magnetic field dependence to reported one, is tripled compared with the 2DEG without the La7/8Sr1/8MnO3 spacer. There are evidences that fast charge carriers of the 2DEG are responsible for the magnetic coupling between Mn ions in 2DEG. The present work opens a new avenue towards magnetic 2DEG. |
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G60.00130: Symmetry mismatch-driven perpendicular magnetic anisotropy for La2/3Sr1/3MnO3/LaCoO2.5 (LSMO/LCO) heterostructures Jing Zhang, Zhicheng Zhong, Xiangxiang Guan, Jine Zhang, Furong Han, Hui Zhang, Baogen Shen, Jirong Sun Grouping different transition metal oxides (TMOs) together by interface engineering is an important route towards emergent phenomenon. While most of the previous works focused on the interface effects on perovskite/perovskite (P/P) heterostructures, herein we report on a fabrication of perovskite/brownmillerite (P/B)type La2/3Sr1/3MnO3/LaCoO2.5 (LSMO/LCO) heterostructure on (001)-orientened SrTiO3 substrates.Through the magnetic measurements, we find the perpendicular magnetic anisotropy (PMA) of the LSMO layer, which keeps in-plane easy axis under tensile strian.As evidenced by high resolution lattice structure analysis and density functional theory calculations, alternatively stacking of perovskite La2/3Sr1/3MnO3 and brownmillerite LaCoO2.5 results in a distinct relaxation of the neighboring MnO6 and CoO4 polyhedra that is not seen at the P/P interface,causing distinct orbital reconstructions thus the PMA. Moreover, the PMA is robust, with an anisotropy constant two orders of magnitude greater than that the in-plane anisotropy of the P/P interface.The present work demonstrates the great potential of symmetry engineering in designing artificial materials on demand. |
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G60.00131: Quasianalytical treatment of the spin Seebeck effect on the Na2 molecule Georgios Lefkidis, Sebastian Reyes In the field of spin caloric transport one seeks to both understand and utilize thermal effects to control spin and charge transport. The discovery of the spin-Seebeck effect (SSE), where a thermal gradient induces a spin-voltage difference parallel to the wire, has given a major impetus to the field of spin caloritronics [1]. |
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G60.00132: Microscopic theory of all-optical spin switching in
ferromagnets, ferrimagnets and Laves phase C15 compounds Guoping Zhang, Yihua Bai, Thomas George Growing interest in all-optical spin switching has |
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G60.00133: Abstract Withdrawn
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G60.00134: Frustrated Magnetism in RE2SrAl2O7 (RE = Gd, Tb, Ho) with a 2D Edge-Sharing-Tetrahedral Lattice Alemayehu Admasu, Jaewook Kim, Huibo Cao, Stephen Blundell, Sang-Wook Cheong Single crystals of the refractory aluminate series RE2SrAl2O7 (RE=Gd, Tb, Ho) are grown for the first time using a laser-diode-heated floating zone method. These series belong to the Ruddlesden–Popper phase of general formula SrREnAlnO3n+1 with n=2 [1]. The structure is a periodic stacking of a rock-salt layer and a double perovskite block where rare earth cations are arranged in two square 2D lattices lying on top of each other but shifted by (1/2, 1/2). The two square 2D lattices of the only magnetic ions in these systems, RE3+, can be viewed as a 2D edge-sharing-tetrahedral lattice with nearest-neighbour antiferromagnetic interactions resulting in a 2-in, 2-out spin structure, reminiscent of spin ice. Magnetic measurements do not show magnetic order down to 1.8 K, but the susceptibility indicates competing interactions. The question of magnetic ground state and crystalline anisotropy is further investigated by low temperature µSR and neutron scattering experiments. |
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G60.00135: Magnetic Properties of Triangular-Lattice Materials Li4CoTeO6 and Li4NiTeO6 Darian Bender, Ryan Rawl, Martin Mourigal, Haidong Zhou In this poster, I will discuss two materials, Li4CoTeO6 and Li4NiTeO6, in which Ni and Co ions with effective spin-1 and spin-1/2 each occupy a triangular lattice. We performed thermodynamic and magnetization measurements which indicate a possible exotic magnetic ground-state in both materials. We then performed elastic neutron scattering, providing additional evidence for exotic magnetism in these materials. The next step of our research will be to perform inelastic neutron scattering on powder samples to probe the nature of the magnetic correlations. |
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G60.00136: Quantum phase transitions in the transverse Ising model with three-spin interactions Osiel Bonfim, Beatriz Boechat, Joao Florencio The ground-state properties of the transverse Ising model with competing three-spin interactions are investigated using exact diagonalization for lattice sizes up to 24 spins. The phase diagram in the $(J_2,J_3)$-plane for fixed magnetic field is obtained using the fidelity susceptibility method. Here, $J_2 < 0$ (AF) and $J_3$ > 0 (F) are the energy couplings for the two- and three-spin interactions, respectively. The ground-state phase diagram shows an antiferromagnetic phase near the $J_2$-axis and a <1,2>-phase near the $J_3$-axis, which are always separated by a paramagnetic phase in between them. Therefore we do not observe any tricrical point, contrary to what has been reported in the literature. |
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G60.00137: Monte-Carlo study of dipolar spin ice under uni-axial pressure Richard Edberg, Patrik Henelius The spin-ice materials are exemplars of magnetic frustration in three dimensions. |
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G60.00138: Reentrant Spin Glass and Mixed Phases in Amorphous EuTiO3 Uppalaiah Erugu Amorphization of magnets disturbs the various competing exchange interactions and gives unique magnetic properties. Such unique properties are evident in amorphous EuTiO3 (ETO) films as it exhibits ferromagnetic (FM) order in contrast to its crystalline antiferromagnet counterpart. Here we present the consequences of amorphization of ETO - the existence of reentrant spin glass (RSG) phase and the mixed phase of RSG and FM ordering using AC susceptibility (χ). The amorphous films were prepared with pulsed laser deposition. The FM and RSG phase transitions are observed around Tc = 6.2 K and TSG = 4.2 K respectively. To understand the magnetic nature of RSG, the linear and non-linear χ have been measured. The real and imaginary linear χ exhibit peaks at the two phase transitions. The peak at Tc is frequency independent while the other peak at TSG shifts to higher temperatures with decreasing height as the frequency is increased. The presence of χ2 signal even below TSG indicates the coexistence of SG state with FM order. Moreover, the divergence of χ3 at TSG confirms the RSG phase transition. |
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G60.00139: Magnetic properties of Rare Earth Spinels Pablo De la Mora, Andrés Gallegos
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G60.00140: Effects of element substitutions on frustrated magnetism of chromite spinel ZnCr2O4 Takayoshi Kusada, Hayato Yamada, Tadataka Watanabe Cubic spinel chromite ZnCr2O4 is a geometrically-frustrated antiferromagnet with the Neel temperature TN = 12.5 K, and the Weiss temperature θW = -390 K. The magnetism of this compound is fully dominated by the orbital-inactive Cr3+ (3d3) with spin S = 3/2, which forms a sublattice of corner-sharing tetrahedra (pyrochlore lattice). We study effects of element substitutions on the geometrically-frustrated magnetism of ZnCr2O4 by investigating structural and magnetic properties of polycrystalline Zn(Cr1-xFex)2O4, Zn(Cr1-xVx)2O4, and Zn(Cr1-xMnx)2O4. For these mixed crystals, the substituted Fe3+ (3d5) with S = 5/2 is an orbital-inactive ion, but V3+ (3d2) with S = 1 and Mn3+ (3d4) with S = 2 are orbital-active ions. The experiments reveal that the antiferromagnetic order of ZnCr2O4 is sensitively suppressed by the element substitutions, and instead, the spin-glass-like behavior appears at low temperatures below ~ 10 K. This result implies the competition of geometrical and bond frustrations in Zn(Cr1-xFex)2O4, Zn(Cr1-xVx)2O4, and Zn(Cr1-xMnx)2O4. |
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G60.00141: Structural Refinement of Potential Quantum Spin Liquid Li2RhO3 via Neutron Diffraction Erik Lamb, Christian Balz, Clarina Dela Cruz, Stephen Nagler Interest in Kitaev materials stems from their potential to realize a quantum spin liquid ground state with Majorana-Fermion excitations that follow non-Abelian statistics useful for quantum computing. The newly synthesized honeycomb rhodate Li2RhO3 is a promising candidate material for bond directional Kitaev interactions as it is isostructural with Na2IrO3, which exhibits dominant Kitaev coupling in its magnetic Hamiltonian. Additionally, Li2RhO3 lacks the highly neutron absorbing Iridium ions of Na2IrO3, making it well suited for investigation via neutron scattering. High resolution neutron powder diffraction was performed on Li2RhO3 at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). Because Li2RhO3 is comprised of nearly decoupled hexagonal planes, it is prone to stacking faults which can alter the ground state. Therefore, we present refinements on collected neutron diffraction data via the Rietveld method using the FullProf Suite and discuss site disorder and stacking faults in Li2RhO3. |
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G60.00142: Probing short-ranged order in spin-liquid Gd3Ga5O12 by spin Seebeck effect Changjiang Liu, Stephen Wu, John Pearson, Nicholas D'Ambrumenil, J Jiang, Anand Bhattacharya Geometrically frustrated magnets have been predicted to host many novel states such as quantum spin liquids and spin ices. A characteristic of these states is the lack of long-range magnetic order, which makes it very difficult to detect them using standard experimental methods. Here, we demonstrate that an application of thermal gradient to the geometrically frustrated spin-liquid Gd3Ga5O12 (GGG) gives rise to a pure spin current, a phenomenon known as spin Seebeck effect (SSE). At low temperatures (2 – 5 K), we observe that the spin current is modulated by a field-induced antiferromagnetic ordering in GGG. These magnetic orderings are short range in character and show distinct anisotropies, also confirmed by our model calculations of the spin configuration. Notably, these structures are not observed in neutron scattering measurements at T > 0.9 K. Additionally, previously unexplored spin excitations in the high field regime are revealed in our SSE measurement. Our findings suggest that SSE is a new and sensitive probe for emergent states in geometrically frustrated magnets. |
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G60.00143: Magnetism of spinel cobaltite ACo2O4 (A = Zn and Li) Bungo Nakagawa, Tadataka Watanabe Cubic spinel cobaltites ZnCo2O4 and LiCo2O4 are expected to be geometrically-frustrated magnets, where magnetic Co ions form the sublattice of corner sharing tetrahedra (pyrochlore lattice). For ZnCo2O4, the magnetism is expected to be dominated by Co3+ (3d 6), which has orbital degentracy in the high-spin state. For LiCo2O4, the magnetism is expected to be dominated by Co3.5+ (3d 5.5), which has orbital and charge degeneracies. We synthesized plycrystals of ZnCo2O4 and LiCo2O4 to investigate the structural and magnetic properties. ZnCo2O4 exhibits the absence of magnetic transition at temperatures down to ~ 2 K, although the magnetic susceptibility measurements in this compound reveal the antiferromagnetic Weiss temperature qW ~ -130 K. LiCo2O4, on the other hand, exhibits an antiferromagnetic transition at TN ~ 30 K with the antiferromagnetic Weiss temperature qW ~ -110 K. The experimental results suggest that, while ZnCo2O4 is a highly-frustrated magnet, the antiferromagnetic transition in LiCo2O4 is driven by the charge degree of freedom. |
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G60.00144: Abstract Withdrawn
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G60.00145: Synthesis and Magnetic Characterization of Geometrically Frustrated Double Perovskites Demetrios Papakostas, Connor Williams, Jeremy Carlo Geometric magnetic frustration occurs when magnetic ions are arranged spatially such that magnetic order is inhibited. Frustrated materials are of interest to the research community due to their rich magnetic phase diagrams, exhibiting exotic physics and high sensitivity to parameters such as doping and structural distortion. We have successfully synthesized and performed SQUID susceptibility measurements on the following 4d1 and 5d1 (Mo5+/W5+) double perovskite compounds: Ba2YbMoO6, Ba2LuWO6, Ba2YWO6, Ba2ScMoO6, and Sr2ScMoO6 |
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G60.00146: Phase transitions of the bilayered spin one XY model Antonio Pires The bilayered spin one quantum antiferromagnetic XY model with single ion anisotropy on a square lattice is studied using two different approaches. In the disordered phase we use the SU(3) Schwinger boson representation followed by a mean field decoupling. This technique is appropriate to study disordered phases in the presence of easy plane single ion anisotropy. The phase diagram at zero temperature is obtained. The ratio r =JT/J between the interlayer JT to the intralayer J exchange interactions exhibits a quantum phase transition at a critical ratio rc = 21.725 that separates the small r Neel phase from the large r quantum disordered paramagnet. There are two different ways to destroy the Neel order, by increasing the anisotropy parameter D or increasing the coupling between the layers. We calculate the dispersion relation in the Brillouin zone for some values of D and r, and the gap as a function of r and temperature. The ordered phase is studied using a self consistent harmonic approximation that takes into account topological effects. We calculate the Kosterlitz-Thouless transition temperature as a function of r. |
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G60.00147: Very High Frequency Electron Paramagnetic Resonance Studies on γ-BaCo2(PO4)2 Luis Martinez, Christian Saiz, Harikrishnan Nair, Jesse Brown, Kate Ross, Johan Van Tol, Srinivasa Rao γ-BaCo2(PO4)2 (γ-BCPO) is a quasi-two-dimensional frustrated honeycomb magnet with two separate short-range magnetic order – collinear and helical. Through magnetometry, specific heat and inelastic neutron studies, it was confirmed that the magnetism of γ-BCPO balances at the edge of the competing phases of the XXZ J1-J2-J3 model. To better understand the local magnetism, very high frequency (120 – 614.4 GHz) electron paramagnetic resonance (VHF-EPR) measurements have been performed from 1.5 – 80 K. At any applied microwave frequency, we found no EPR signal from γ-BCPO above 20K. For T < 20 K, a broad signal is visible at low fields, with the spectral features better defined. As the frequency changed from 120 - 336 GHz, the broad signal split into several narrow modes, and for frequency 406.6 GHz and 614.4 GHz, a broad, but complete signal appeared with no splitting. The effective g-value shifts from g = 14.62 to 11.18 as the frequency increased from 406.6 to 614.4 GHz, in line with a magnetic gap of 300 GHz. The EPR signal narrows and shifts to lower fields as the temperature is lowered from 20 – 1.5 K. These features indicate that the resonances are likely related to antiferromagnetic modes because of large internal fields due to complex magnetic interactions in γ-BCPO. |
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G60.00148: Theory of a quantum spin liquid in hydrogen-intercalated honeycomb iridate, H3LiIr2O6 Wonjune Choi, Kevin Slagle, Li Ern Chern, Yong-Baek Kim We propose a theoretical model for a gapless spin liquid phase that may have been observed in a recent experiment on H3LiIr2O6. Despite the insulating and non-magnetic nature of the material, the specific heat coefficient C/T∼1/√T in zero magnetic field and C/T∼T/B3/2 with finite magnetic field B have been observed. In addition, the NMR relaxation rate shows 1/(T1T)∼(C/T)2. Motivated by the fact that the interlayer/in-plane lattice parameters are reduced/elongated by the hydrogen-intercalation of the parent compound Li2IrO3, we consider four layers of the Kitaev honeycomb lattice model with additional interlayer exchange interactions. It is shown that the resulting spin liquid excitations reside mostly in the top and bottom layers of such a layered structure and possess a quartic dispersion. In an applied magnetic field, each quartic mode is split into four Majorana cones with the velocity v∼B3/4. We suggest that the spin liquid phase in these "defect" layers, placed between different stacking patterns of the honeycomb layers, can explain the major phenomenology of the experiment, which can be taken as evidence that the Kitaev interaction plays the primary role in the formation of a quantum spin liquid in this material. |
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G60.00149: Element substitution effects on magnetism of cadmium chromite spinel CdCr2O4 Yuto Sugaya, Hayato Yamada, Tadataka Watanabe Cadmium chromite spinel CdCr2O4 is a geometrically-frustrated magnet with the Neel temperature TN ~ 8 K, and the Weiss temperature qw ~ -70 K. The magnetic properties of this compound are fully dominated by the orbital-inactive Cr3+ (3d3) with spin S = 3/2 residing on the pyrochlore network. To study the element substitution effects on the geometrically-frustrated magnetism of CdCr2O4, we investigate structural and magnetic properties of polycrystalline Cd(Cr1-xFex)2O4,Cd(Cr1-xVx)2O4, and Cd(Cr1-xMnx)2O4. For these mixed crystals, the substituted Fe3+ (3d5) with S =5/2 is an orbital-inactive ion, but V3+ (3d2) with S = 1 and Mn3+ (3d4) with S = 2 are orbital-active ions. The experiments reveal that the antiferromagnetic order of CdCr2O4 is sensitively suppressed by the element substitutions, and instead, the spin-glass-like behavior appears at low temperatures below ~ 10 K. This result implies the competition of geometrical and bond frustrations in Cd(Cr1-xFex)2O4, Cd(Cr1-xVx)2O4, and Cd(Cr1-xMnx)2O4. |
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G60.00150: Doping effects on itinerant-electron magnetism of Laves compound AFe2 (A = Ti and Zr) Yuki Takei, Sou Enomoto, Tadataka Watanabe Laves compounds TiFe2 and ZrFe2 have C14-type hexagonal and C15-type cubic crystal structures, respectively. C14-type hexagonal crystal structure of TiFe2 contains Kagome lattice sheets of Fe atoms. C15-type cubic crystal structure of ZrFe2 contains Fe sublattice of corner-sharing tetrahedra (pyrochlore lattice). TiFe2 and ZrFe2 both exhibits itinerant-electron magnetism, where Fe 3d electrons are expected to play dominate role. While ZrFe2 exhibits a ferromagnetic transition at TC ~ 620 K, TiFe2 exhibits an antiferromagnetic transition at TN ~ 290 K. To study doping effects on the itinerant-electron magnetism of TiFe2 and ZrFe2, we investigate structural, electric, and magnetic properties of polycrystalline Ti(Fe1-xCox)2 and Zr(Fe1-xCox)2. The experiments reveal that, for Zr(Fe1-xCox)2, the ferromagnetic order is suppressed with increasing Co concentration x. On the other hand, Ti(Fe1-xCox)2 is found to exhibit a variety of antiferromagnetic and ferromagnetic orders depending on Co concentration x. |
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G60.00151: Synthesis and Structural Characterization of Geometrically Frustrated Doube Perovskites Connor Williams, Demetrios Papakostas, Jeremy Carlo In geometrically frustrated materials, magnetic order is inhibited by the arrangement of magnetic ions. Typically seen with triangular or tetrahedrally coordinated moments favoring antiparallel (antiferromagnetic) alignment, frustrated materials exhibit a variety of magnetic ground states due to the cancellation of normally dominant interactions, providing a window into exotic physics, and thus have attracted great research interest. |
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G60.00152: Element substitution effects on magnetism of cadmium chromite spinel CdCr2O4 Sugaya Yuto, Hayato Yamada, Tadataka Watanabe Cadmium chromite spinel CdCr2O4 is a geometrically-frustrated magnet with the Neel temperature TN ~ 8 K, and the Weiss temperature qw ~ -70 K. The magnetic properties of this compound are fully dominated by the orbital-inactive Cr3+ (3d3) with spin S = 3/2 residing on the pyrochlore network. To study the element substitution effects on the geometrically-frustrated magnetism of CdCr2O4, we investigate structural and magnetic properties of polycrystalline Cd(Cr1-xFex)2O4,Cd(Cr1-xVx)2O4, and Cd(Cr1-xMnx)2O4. For these mixed crystals, the substituted Fe3+ (3d5) with S =5/2 is an orbital-inactive ion, but V3+ (3d2) with S = 1 and Mn3+ (3d4) with S = 2 are orbital-active ions. The experiments reveal that the antiferromagnetic order of CdCr2O4 is sensitively suppressed by the element substitutions, and instead, the spin-glass-like behavior appears at low temperatures below ~ 10 K. This result implies the competition of geometrical and bond frustrations in Cd(Cr1-xFex)2O4, Cd(Cr1-xVx)2O4, and Cd(Cr1-xMnx)2O4. |
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G60.00153: Spin Selectivity in Photoelectron Transmission through Self-Assembled Monolayers of Mercurated DNA Helices John Abendroth, Matthew Ye, Dominik Stemer, Kevin Cheung, Mohammed El Hadri, Eric Fullerton, Paul Weiss Chiral molecules have been shown to act as electron spin filters at room temperature, however the mechanisms remain elusive. Molecular spin-orbit coupling is thought to play a dominant role due to the chiral electrostatic potential that breaks inversion symmetry experienced by transmitted electrons. To test this hypothesis, we designed helical DNA molecules that contain mercury atoms bound at base-pair mismatches. By controlling the number and location of mercury atoms along the DNA axis, we manipulate the strength of the helical spin-orbit field via the heavy atom effect. Monolayers of mercurated DNA are formed on ferromagnetic substrates. Using ultraviolet photoemission spectroscopy, efficiencies of electron transmission through DNA monolayers is probed. Photoelectrons from ferromagnetic surfaces are spin polarized, while adsorbed chiral molecules act as spin filters. Thus, emission intensities and energies of the secondary-electron cutoff are compared using DNA monolayers with varying mercury content. Demonstrating control over molecular spin-orbit coupling to tune spin selectivity by chiral molecules is critical to assess their practically for spintronics applications. |
(Author Not Attending)
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G60.00154: Skyrmion morphology in ultrathin magnetic films Mohammad Akhtar, I. Gross, A. Hrabec, J. Sampaio, L.J. Martinez, S. Chouaieb, B.J. Shields, P. Maletinsky, A. Thiaville, S. Rohart, Vincent Jacques Nitrogen-vacancy magnetic microscopy is employed in quenching mode as a non-invasive, high resolution tool to investigate the morphology of isolated skyrmions in ultrathin magnetic films [1]. The skyrmion size and shape are found to be strongly affected by local pinning effects and magnetic field history. Micromagnetic simulations including static disorder, based on a physical model of grain-to-grain thickness variations, reproduce all experimental observations and reveal the key role of disorder and magnetic history in the stabilization of skyrmions in ultrathin magnetic films. This work opens the way to an in-depth understanding of skyrmion dynamics in real, disordered media. [1] I. Gross et al. arXiv:1709.06027 (2017). |
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G60.00155: Precipitating Ordered Skyrmion Lattices from Helical Spaghetti Dustin Gilbert, Alexander Grutter, Paul Neves, Guo-Jiun Shu, Fangchang Chou, Kathryn Krycka, Nicholas Butch, Sunxiang Huang, Julie Borchers
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G60.00156: Magneto-Raman Spectroscopy on Vanadium-derived Lacunar Spinel GaV4S8 Gary Knight, Zhengguang Lu, Ganesh Pokharel, Hasitha Suria Arachchige, Andrew Christianson, David Mandrus, Dmitry Smirnov, Komalavalli Thirunavukkuarasu GaV4S8(GaVS) is a magnetic semiconductor with a Neel-type skyrmion phase lattice displaying multiferroic properties [1]. Magnetic susceptibility measurements indicate the presence of a structural transition at 42 K followed by a ferromagnetic order at 12 K [2]. Recent temperature-dependent infrared and Raman spectroscopic measurements identified the various phonon modes and the presence of Jahn-Teller distortions in this compound [3]. To obtain more detailed information on the various exchange interactions in this compound, we performed magneto-Raman measurements at magnetic fields up to 14 T at temperature down to 5 K. In this poster I will present the main results of our magneto-Raman investigations and its implications. |
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G60.00157: Resonant Ultrasonic Spectroscopy: A new access to Skyrmion lattice Yongkang Luo, Shizeng Lin, David Fobes, Nicholas Wakeham, Zhiqi Liu, Eric Bauer, Jonathan Betts, Albert Migliori, Joe Thompson, Marc Janoschek, Boris Maiorov We employed Resonant Ultrasonic Spectroscopy (RUS) measurements as an approach to the Skyrmion crystal (SKX) lattice. The elastic modulus and attenuation of MnSi were systematically investigated. The important findings are: (1) We reported the first complete measurement of the elastic tensor of MnSi with RUS, and studied their behaviors near the SKX phase. The phase diagram is mapped out. (2) In the presence of a DC current, we studied the decoupling of SKX and the crystallographic lattice and got a critical current density jc≈61.8 kA/m2. (3) With a field angular dependent RUS measurement, we observed abrupt changes of the elastic modulus and attenuation when the magnetic field is parallel to the [011] crystallographic direction. Calculations based on phenomenological Ginzburg-Landau theory were performed to understand the nature of magneto-crystalline coupling between the SKX lattice and the underlying crystallographic lattice. |
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G60.00158: Experimental Evidence of Chiral Ferrimagnetism in Amorphous Materials Robert Streubel, Charles-Henri Lambert, Noah Kent, Peter Ercius, Alpha N'Diaye, Colin Ophus, Sayeef Salahuddin, Peter Fischer Inversion symmetry breaking has become a vital research in modern magnetism with phenomena including Rashba effect, spin Hall effect and Dzyaloshinskii-Moriya interaction (DMI). The latter one may stabilize chiral spin textures with topologically non-trivial properties, such as Skyrmions. So far, chiral spin textures have mainly been studied in helimagnets and thin ferromagnets with heavy-element capping. Here, we show, using the example of chiral ferrimagnetism in amorphous GdCo, that the concept of chirality driven by interfacial DMI can be generalized to complex multicomponent systems. Utilizing Lorentz microscopy and X-ray magnetic circular dichroism spectroscopy, and tailoring thickness, capping and rare-earth composition, we find that a 2nm-thick GdCo film preserves ferrimagnetism and stabilizes chiral domain walls. The type of chiral domain walls depends on the rare-earth composition/saturation magnetization, enabling a possible temperature control of the intrinsic properties of ferrimagnetic domain walls. |
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G60.00159: Characterizing the spin-polarization of bulk antiferromagnetic tips using single atom magnets Patrick Forrester, Tobias Bilgeri, François Patthey, Harald Brune, Fabian Natterer
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G60.00160: Emerging exchange bias and magnetic coupled layer at molecular interface Junhyeon Jo, Inseon Oh, Mi-JIn Jin, Jungmin Park, Jung-Woo Yoo Exchange bias (EB) effect is one of the integral part in spintronics which describes a magnetic coupling at the interface between a ferromagnetic (FM) and an antiferromagnetic material (AFM). Recently, this effect has been received great attention in a logical memory device by acting as 'effective magnetic field' without external magnetic field. In this report, we realize the EB effect at the interface between small molecule and ferromagnetic metal thin film system. Electrical transport and SQUID-VSM analyses show a clear EB and further newly developed exchange coupled layer at the organic/inorganic interface, giving us opportunity to realize new functionalities by tuning the unique interface. Several spectroscopy data support the phenomenon in detail and shed light on the origin of the interfacial EB in the system. This research will be the foundation of a tunable organic/inorganic device in spintronics without external magnetic field. |
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G60.00161: Photoinduced Magneto-Structural Interplay at the Interface of Core@Shell Nanoparticles of RbCoFe@KNiCr PBA John Cain, Ashley Felts, Daniel Talham, Mark Meisel Core@shell heterostructures of Prussian blue analogues (PBAs), namely RbxCo[Fe(CN)6]y@KaNi[Cr(CN)6]b, show a photoinduced decrease in magnetization when irradiated with white light below Tc = 70 K of the non-photoactive KaNi[Cr(CN)6]b shell [1,2]. This decrease is magnetomechanical in origin, where the photoinduced volume changes of the core and the resulting change of strain in the shell reduce the shell magnetization. A simple model provides an estimate of the strain depth in the shell, but only one core size was studied [2]. The data from three new sets of core@shell heterostructures provide evidence of the core size dependence on the shell strain depth (one set = one RbCoFe PBA core and three KNiCr PBA shells). Increasing the core size from 328 ± 29 nm to 575 ± 113 nm modifies the shell strain depth from ≈ 50 nm to > 90 nm. The assumption of a rigid core fails, and PXRD data show a quantitative model for the strain depth must also account for the effect of the strain induced in the core [2]. SANS studies of the strain-sensitivity of the shell magnetization are being developed and potential samples are presented. |
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G60.00162: Optical and Magnetic Properties of Manganese Phthalocyanine Thin Films Anh Nguyen, Mariyeh Mafi, Thomas Gredig Metallo-phthalocyanine-based thin films have been widely used in applications, such as electronic and photonic devices, organic photovoltaic devices, and gas sensors. Thin films of manganese phthalocyanine with different nanostructures are prepared onto Silicon and glass substrates. Both the magnetic and optical properties are studied. The absorption spectra show prominent peaks in the B- and Q-band as expected for phthalocyanine molecules. The energy band gap is measured from the optical spectrum of the transmission data. From the peak in the B-band, the fundamental energy gap near 3.6 eV can be estimated, which is higher than for iron phthalocyanine thin films. A comparison of the magnetic measurements of manganese phthalocyanine thin films with iron phthalocyanine thin films is made. These results provide insight towards designing organic-based spintronic devices. |
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G60.00163: Magneto-Raman Spectroscopy on multiferroic metal-organic framework [(CH3)2NH2]Co(HCOO)3] Rachael Richardson, Zhengguang Lu, Dmitry Smirnov, David Mandrus, Komalavalli Thirunavukkuarasu Designing functional materials is one of the important goals of materials research. One of the route towards achieving this goal involves using organic groups to synthesize wide variety of compounds with intriguing properties. Metal-organic framework is a class of compounds where organic groups are used in combination with transition metal ions to obtain multifunctional materials. Recently, it has been demonstrated that the family of compounds [(CH3)2NH2]M(HCOO)3 (with M=Ni,Mn,Co and Fe) exhibit multiferroic properties [1]. Therefore, several efforts have been made to understand the nature and strength of exchange interactions in these materials [2]. To obtain more information about the interplay between the spin, charge and lattice degrees of freedom, we performed magneto-Raman spectroscopy on [(CH3)2NH2]Co(HCOO)3 at magnetic fields up to 15 T. In this poster, I will discuss the main results of our investigations and its potential functionality. |
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G60.00164: Spin Filtering in Chiral Quantum Dot Assemblies Dominik Stemer, John Abendroth, Paul Weiss Chiral molecules have recently attracted attention due to their capacity to act as room temperature spin filters without the need for strong magnetic fields. Chiral signatures have been identified in quantum dots (QDs) coated with chiral ligands using circular dichroism (CD). These CD signals are intrinsic to the QDs. The CD signals are dependent on QD size, and so may be tuned. Chiral QD assemblies are covalently tethered to ferromagnetic substrates. We engineer a system with two spin-selective processes: charge transport through the chiral ensemble and charge injection into the magnetized substrate. The combination of these processes enables quantitative analyses of spin filtering through chiral QD assemblies as a function of various experimental parameters. We compare fluorescence lifetime asymmetry in chiral QD ensembles with varying QD size and tether length. Shorter fluorescent lifetimes corresponds to lower barriers to charge transfer through the chiral ensemble and into the substrate. By measuring fluorescent lifetime asymmetry, we quantitatively determine the spin-filtering efficiency, and thereby the practicality of incorporating chiral QDs into spintronic devices as spin-polarized electron sources. |
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G60.00165: Magnetism and magnetocrystalline anisotropy in single-layer PtSe2: Interplay between strain and vacancy Wei Zhang, Lifa Zhang The exploration of the magnetism is a hot topic in the field of 2D materials research because most of the well known 2D materials such as graphene, h-BN, single-layer (1L) transition-metal dichalcogenide (TMD) are intrinsically nonmagnetic. In our recent work, using the first-principles calculations, we systematically studied the magnetic and electronic properties of the newly synthesized 1L-TMD PtSe2. We found the selenium vacancy (VSe) or strain alone could not induce the magnetism. However, an interplay between VSe and strain led to the magnetism due to the breaking of Pt-Pt metallic bonds. Different from the case of 1L-MoS2 with VS, the defective 1L-PtSe2 had the spatially extended spin density, which was responsible for the obtained long range ferromagnetic coupling. Moreover, the 1L-PtSe2 with VSe underwent a spin reorientation transition from out-of-plane to in-plane magnetization, accompanying a maximum magnetocrystalline anisotropy energy of 9~10.6 meV/VSe. Our work show that the strain not only can effectively tune the magnetism but also can manipulate the magnetization direction of 1L-TMDs. |
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G60.00166: Spin Seebeck effect in the antiferromagnet nickel oxide at room temperature José Holanda da Silva Júnior, D. S. Maior, O. Alves Santos, L. H. Vilela-Leão, Joaquim Mendes, Antonio Azevedo, R. L. Rodríguez-Suárez, Sergio Rezende NiO is a room-temperature antiferromagnetic (AF) insulator with important applications in AF spintronics. It is considered a prototypical AF material with a simple magnetic structure with two sublattice spins aligned in easy planes and having small in-plane magnetic anisotropy. Recently the spin Seebeck effect (SSE) has been observed, at low temperatures and high magnetic fields, in bilayers made of the antiferromagnets MnF2 and Cr2O3 with Pt-capping layer. Usually, the SSE is detected by an electric voltage generated in the metallic layer in contact with the magnetic film produced by the spin to charge current conversion through the inverse spin Hall effect (ISHE) [1]. Here we report measurements of the SSE in a film of antiferromagnetic NiO at room temperature and low magnetic fields. The detection of the spin current generated by the thermal gradient in the NiO layer is made by means of the ISHE in the non magnetic metals Pt and Ta, in the AF metal IrMn and in the ferromagnetic metal permalloy [2]. |
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G60.00167: Spin to Charge Current Conversion in the Topological Insulator (Bi0.22Sb0.78)2Te3 Films at Room Temperature Joaquim Mendes, Obed Alves Santos, Jose Holanda, Renan Loreto, Clodoaldo de Araujo, Cui-Zu Chang, Jagadeesh Moodera, Antonio Azevedo, Sergio Rezende Topological Insulators (TIs) constitute a new class of quantum materials, and here we report spin to charge current conversion in an intrinsic TI (Bi0.22Sb0.78)2Te3 film at room temperature. The spin currents are generated in a thin layer of permalloy (Py) by two different processes, spin pumping effect (SPE) and spin Seebeck effect (SSE). In the first process, we use microwave-driven ferromagnetic resonance of the Py film to generate a SPE spin current that is injected into the TI (Bi0.22Sb0.78)2Te3 layer in direct contact with Py. In the second process, we use the SSE in the longitudinal configuration in Py without contamination by the Nernst effect made possible with the use of a thin NiO layer between the Py and (Bi0.22Sb0.78)2Te3 layers. The spin-to-charge current conversion is attributed to the inverse Edelstein effect (IEE) by the spin-momentum locking in the electron Fermi contours due to the Rashba field. The measurements by the two techniques yield very similar values for the IEE parameter, which are larger than the reported values in the previous studies on TIs. |
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G60.00168: Efficient Excitation of Perpendicular Standing Spin-Waves in Undulating CoFeB Films Aryan Navabi, Cai Chen, Anthony Barra, Mohsen Yazdani, Guoqiang Yu, Mohammed Aldosary, Junxue Li, Mohammad Montazeri, Kin Wong, Jing Shi, Greg Carman, Abdon Sepulveda, Pedram Khalili Amiri, Kang Wang We report on efficient excitation of perpendicular standing spin-waves (PSSWs) in undulating CoFeB films. PSSWs are exchange dominated spin-waves and have been observed through non-uniform excitation of spin-waves across a ferromagnetic (FM) layer film, and current methods have proven to be inefficient, resulting in weak excitations. We achieve efficient coupling to PSSWs by creating periodic undulations in 100 nm thick CoFeB. The S11 parameter was measured using coplanar waveguides and a network analyzer. An additional mode, not present in flat control samples, was observed for undulating CoFeB films. We attributed this mode to PSSWs being excited due to the non-uniform excitation of spin-waves across the thickness of the FM film. The dispersion relations for Magnetostatic surface spin-waves (MSSW) and PSSWs were used to fit the measured curves and determine key material and excitation parameters such as the exchange constant. Simulations were also used to visualize the dynamics of the oscillations in the CoFeB film. Efficient excitation of such exchange coupled spin-waves can help realize spintronic applications where exchange coupled magnetic oscillations are critical. These undulating structures also provide a simple method to measure the exchange constant for thin FM films. |
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G60.00169: Non-Uniform Strain-Driven Magnetic Domain Wall Motion in PMN-PT/Ni Microstructures Cai Chen, Roberto Lo Conte, Michael Cui, Jeffrey Bokor, Greg Carman, Abdon Sepulveda Strain-mediated multiferroic hetero-structures are of great interest since they offer a possible path towards high energy-efficient magnetic memory and logic devices. In this simulation work, a finite difference model is developed to study the strain induced magnetic domain wall (DW) motion in micron size Ni squares onto a PMN-PT substrate. The analysis consists of solving the coupled micromagnetic with elastodynamics. In the model, a non-uniform strain is introduced inside the Ni squares in order to reproduce real devices’ conditions. Initially a magnetic Landau flux-closure state is formed in Ni structures. As an electric field is applied generating compressive strain along the diagonal of the Ni square, a two-domain state forms consisting of two anti-parallel magnetic domains, separated by a DW. A further increase of the electric field produces a lateral motion of the DW. Such DW motion is understood as a result of the minimization of its energy. Good agreement with experimental result is produced by the model. This model helps to better understand the strain-induced magnetic reorientation and DW motion in real multiferroic systems. |
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G60.00170: Controlled domain evolution in magnetic heterostructures with perpendicular magnetic anisotropy and interfacial DMI Jagodage Kasuni Nanayakkara, Madison Hanberry, Sergei Urazhdin, Alexander Kozhanov Controlled evolution of magnetic textures in films with perpendicular magnetic anisotropy (PMA) is potentially important for spintronic applications such as domain wall logic in unpatterned structures and dynamic magnonic structures. In this work we use magneto-optic Kerr microscopy to study domain evolution in CoNi and CoNiPt multilayer heterostructures in presence of out-of-plane and in-plane magnetic fields. While bubble domains form in 1-4 layer structures, labyrinth-like domains are characteristic for thicker films (e.g. 10 repetitions).1 Interfacial Dzyaloshinsky Moriya Interaction in these materials result in asymmetric domain wall propagation controlled by in-plane magnetic field.2 We demonstrate capability of controlled stripe domain growth at any direction defined by the in-plane magnetic field as well as forming more complex magnetic textures “drawn” by stripe domains, such as variable angle domain intersection, circles and circle segments. We discuss the dipole, exchange and DMI interaction effects on the domain evolution in studied samples. |
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G60.00171: Origin of the Sun’s Electromagnetic Fields and Solar Cycles, or Solar Cycles Hypothesis Hassan Gholibeigian, Kazem Gholibeigian Sun’s core dislocation happens due to effect of gravitational fields of the planets to the Sun. In other words, dislocated Sun’s core rotates a round per 24-35 days in radiation zone around the Sun’s center inverse of the Sun’s rotation while it is rotating a round per 6 days around itself. Direction of the Sun’s magnetic field lines from South Pole to the sky is an observable factor. This variable large scale forced convection system generates huge momentum of inertia as the main source of the Sun’s gravitational field, Sun’s deformation, and speed-up the fusion, and hot gas “soup” motion with many free charged particles as a source of magnetic field. Moreover, this mechanism generates a thermo-magnetic shear zone between the core and radiation zone which rotates 3-4 times faster than tachocline and generates stronger magnetic field. This mechanism indicates that Jupiter with 11,856 years orbit period may be the main cause of the 11-year solar cycles. When Jupiter approaches the Sun and moves away, gravitational field in perihelion becomes 2.71 times larger. During this time (2-3 years), Earth passes 2-3 times through it, this dynamic system becomes more active inside the Sun, Jupiter, and Earth. When they are aligned, the peak of solar cycles occur, which is predictable. |
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G60.00172: Origin of the Sun’s Electromagnetic Fields and Solar Cycles, or Solar Cycles Hypothesis Hassan Gholibeigian, Kazem Gholibeigian Sun’s core dislocation happens due to effect of unbalanced gravitational fields of the planets to the Sun. In other words, dislocated Sun’s core rotates a round per 24-35 days in radiation zone around Sun’s center inverse of the Sun’s rotation while it is rotating a round per 6 days around itself. Direction of the Sun’s magnetic field lines from South Pole to the sky is an observable factor. This variable large scale forced convection system generates huge momentum of inertia as the main source of the Sun’s gravitational field, Sun’s deformation, and speed-up the fusion, and hot gas “soup” motion with many free charged particles as a source of magnetic field. Moreover, this mechanism generates a thermo-magnetic shear zone between the core and radiation zone which rotates 3-4 times faster than tachocline and generates stronger magnetic field. This mechanism indicates that Jupiter with 11,856 years orbit period may be the main cause of the 11-year solar cycles. When Jupiter approaches the Sun and moves away, gravitational field in perihelion becomes 2.71 times larger. During this time (2-3 years), Earth passes 2-3 times through it, this dynamic system becomes more active inside the Sun, Jupiter, and Earth. When they are aligned, the peak of solar cycles occur, which is predictable. |
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G60.00173: Origin of the Sun’s Electromagnetic Fields and Solar Cycles, or “Solar Cycles Hypothesis” (SCH) Hassan Gholibeigian A permanent variable dislocation of the Sun’s core has been happening inside the radiation zone due to effect of unbalanced gravitational fields of the planets to the Sun. In this way, Jupiter has important role because it has strongest gravitational field in solar system after Sun. |
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G60.00174: Origin of the Sun’s Electromagnetic Fields and Solar Cycles, or Solar Cycles Hypothesis Hassan Gholibeigian, Kazem Gholibeigian Sun’s core dislocation happens due to effect of unbalanced gravitational fields of the planets to the Sun. In other words, dislocated Sun’s core rotates a round per 24-35 days in radiation zone around the Sun’s center inverse of the Sun’s rotation while it is rotating a round per 6 days around itself . Direction of the Sun’s magnetic field lines from South Pole to the sky is an observable factor. This variable forced convection system generates momentum of inertia as the main source of the Sun’s gravitational field, Sun’s deformation, and speed-up the fusion and hot gas “soup” motion with many free charged particles as a source of magnetic field. Also, this mechanism generates a thermo-magnetic shear zone between the core and radiation zone which rotates 3-4 times faster than tachocline and generates stronger magnetic field. This mechanism leads us that the Jupiter with 11,856 years orbit period may be the main cause of the 11-year solar cycles. When it is approaching to the Sun and getting away from it, gravitational field in perihelion becomes 2.71 times more. During this time (2-3 years), Earth passes 2-3 times through it, this dynamic system becomes more active inside the Sun, Jupiter and Earth. When they are in a line, the peak of solar cycles occur, which is predictable. |
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G60.00175: Absence of static magnetic order in non-superconducting FeSe thin films on SrTiO3(001) revealed by the magnetism of Se vacancies Weijiong Chen, Zijun Tian, Ping Li, Weidong Luo, C. L. Gao FeSe, as the simplest iron-based superconductor, invokes tremendous studies on its electronic and magnetic properties. A puzzling phenomenon revealed by the experiments is that FeSe crystal undergoes a nematic structural phase transition around 90 K but without any antiferromagnetic transition in ambient pressure. However, this is not conclusive for non-superconducting FeSe multilayer films due to the stress caused by lattice mismatch and the difficulty in measuring the magnetism in the thin film limit. Here, the absence of static magnetic order is directly revealed by the magnetism of an isolated Se vacancy in FeSe multilayer films grown on SrTiO3(001) measured with spin-polarized scanning tunneling microscopy on the atomic scale. Symmetry analysis and first-principles calculation further confirmed the nonmagnetic ground state of FeSe. The discrepancy between local density approximation and generalized gradient approximation implies FeSe is near a magnetic critical point. |
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G60.00176: Ultrasound velocity measurements in perovskite cobaltites LaCoO3 and La (Co0.99Ni0.01)O3 Ryuichi Okada, Keisuke Tomiyasu, Tadataka Watanabe Perovskite cobaltite LaCoO3 has attracted much interest due to the possible occurrence of the spin-crossover phenomena. The spin state of Co3+ in this compound is considered to change from high-spin to low-spin state on cooling; from high-spin to “magnetic” low-spin state at ~ 100 K, and from “magnetic” to “nonmagnetic” low-spin state at ~ 20 K. Furthermore, for LaCoO3, it was recently suggested that, in the low-temperature “nonmagnetic” low-spin state, the light Ni substitution for Co induces the formation of Ni-centered ferromagnetic spin-state clusters. To study the spin states of LaCoO3 and lightly Ni-substituted LaCoO3 from the viewpoint of the spin-lattice coupling, we performed ultrasound velocity measurements in single crystals of LaCoO3 and La (Co0.99Ni0.01)O3. In the temperature dependence of the elastic moduli, we observed elastic anomalies in these compounds, which suggest the coupling of lattice to local magnetic excitations. Additionally, for LaCoO3, we observed a discontinuous elastic anomaly at ~ 100 K, which indicates the occurrence of phase transition. |
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G60.00177: Switchable and tunable Rashba-type spin splitting in covalent perovskite oxides Julien Varignon, Jacobo Santamaria, Manuel Bibes In transition metal perovskites (ABO3) most physical properties are tunable by structural parameters such as the rotation of the BO6 octahedra. Examples include the Néel temperature of orthoferrites or the bandgap of rare-earth scandates. Since oxides often host large internal electric dipoles and can accommodate heavy elements, they also emerge as prime candidates to display Rashba spin-orbit coupling, through which charge and spin currents can be efficiently interconverted. However, despite a few experimental reports in SrTiO3-based interface systems, the Rashba interaction has been little studied in these materials, and its interplay with structural distortions remain unknown. |
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G60.00178: Metaferroics: Quantum Electric Dipoles Under Strong Magnetic and Electric Fields Christopher Wagner, Pradeep Kumar We present properties of a Hamiltonian that has been developed to serve as a model for a multiferroic with quantum spins and a quantum electric dipole, under the influence of high fields. The Hamiltonian describes both the electric and magnetic degrees of freedom and is similar to the s = 1 model used by Shivaram et al (Phys. Rev. B89, 241107 (2014)) to study metamagnetism in heavy fermions. The two fields interact via a bilinear intereaction. We show the results for the temperature dependence of the linear as well as nonlinear susceptibilities. The linear susceptibility scales inversely with the energy gap between the s = 0 and s = +1, -1 levels. As in the single field case, the nonlinear third order susceptibility is negative at high temperatures. It has a positive peak at a lower temperature. In contrast, the fifth order susceptibility is positive at high temperatures and has a negative peak at lower temperatures. The cross response (dM/dE = dp/dB) is negative, at high temperatures it scales as T-2 and has a peak at a critical temperature. There are a variety of profiles M(B, E, T), depending on the parameters, including some where the meta response consists of more than one step. |
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G60.00179: Spin-dependent Transport in Periodical Magnetic Heterostructures Avag Sahakyan, Anahit Pogosyan, Ruzan Movsesyan, Armen Kocharian The propagation of particles with a half spin is considered in a system consisting of finite number of periodically repeating strongly magnetized barriers separated by nonmagnetic quantum wells. Such model quite well describes the transport properties of some thin-film heterostructures formed by periodically alternating magnetic and nonmagnetic layers of nanotubes. It is assumed that the vectors of the internal fields of barriers are parallel, and the internal field of one barrier is not coplanar with respect to the others. Thus, in a one-dimensional "ferromagnetic" system there is a noncoplanar "defect", the presence of which leads to two-channel scattering of particles-without a spin flip and with its flip. This significantly affects the transport properties of the system, in particular, the spin polarization of the scattered waves turns out to depend not only on the degrees of freedom describing the noncoplanarity of the "defect", but also on its coordinate. |
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G60.00180: Theoretical Study on Anisotropic Magnetoresistance Effects of I//[100], I//[110], and I//[001] for Ferromagnets Satoshi Kokado, Masakiyo Tsunoda We theoretically study anisotropic magnetoresistance (AMR) effects for ferromagnets with a tetragonal crystal field. Here, the tetragonal distortion exists in the [001] direction, the magnetization lies in the (001) plane, and the current I direction, i, is i=I//[100], I//[110], or I//[001]. We extend our previous model [1] to a model including the crystal field effect [2]. Using the model, we obtain analytical expressions of the resistivity and the AMR ratio for each i. In particular, the AMR ratio is expressed as AMRi(φ)=C0i+C2icos(2φ)+C4icos(4φ), where φ is the relative angle between the magnetization direction and the current direction and C0i, C2i, and C4i are coefficients of the constant term, twofold symmetric term, and fourfold symmetric term for i. The coefficients are composed of a spin-orbit coupling constant, an exchange field, a crystal field, and s-s and s-d scattering resistivities. As a result, we confirm the relation of C4I//[100]=-C4I//[110], which was experimentally observed for Fe4N [3] and Ni [4]. |
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G60.00181: Rectifying full-counting statistics in a spin Seebeck engine Gaomin Tang We investigate the rectification effect of a spin Seebeck engine in which the quantum dot (QD) is coupled to both the electronic reservoir and magnetic insulator. The scaled cumulant generating function (SCGF) of the system is expressed in the framework of nonequilibrium Green’s function. We present the rectification and negative differential effect of spin current and its higher order cumulants. The heat engine performances, such as the maximum output power and efficiency are also shown to exhibit rectification and negative differential effect. The strongly fluctuated interfacial electron density of states induced by QD is responsible for these intriguing properties. It can broaden our views of the nonequilibrium thermodynamics by studying the nontrivial phenomena occurred in the two terminal hybrid system involving both electronic and bosonic reservoir. |
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G60.00182: Anomalous Nernst effect in Ir22Mn78/Co20Fe60B20/MgO layers with perpendicular magnetic anisotropy Sa Tu, Junfeng Hu, Guoqiang Yu, Haiming Yu, Chuanpu Liu, Florian Heimbach, Xiangrong Wang, Jianyu Zhang, Youguang Zhang, Amir Hamzic, Kang L Wang, Weisheng Zhao, Jean-Philippe Ansermet The anomalous Nernst effect in perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO thin film is measured using well-defined in-plane temperature gradients.The geometry with out-of-plane magnetic field and in-plane temperature gradient is the natural configuration to avoid longitudinal spin Seebeck effect and allow a precise determination of the temperature gradient. The anomalous Nernst coefficient reaches 1.8 µV/K at room temperature, which is almost 50 times larger than that of Ta/Co20Fe60B20/MgO thin film with perpendicular magnetic anisotropy. The anomalous Nernst and anomalous Hall results in different sample structures reveal that the large Nernst coefficient of Ir22Mn78/Co20Fe60B20/MgO thin film is related to the interface between CoFeB and IrMn. Finally, we point out a possible application of ANE that takes advantage of the perpendicular magnetization to obtain large Nernst voltage, owing to the in-plane geometry of the device. |
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G60.00183: Spin Transport Through Antiferromagnetic/Paramagnetic IrMn Layer Using Second Harmonic Method. Yan Wen, Yuelei Zhao, Xixiang Zhang We investigate the spin transmission through an antiferromagnetic or paramagnetic IrMn layer by using second harmonic methods. The film //Ta5/IrMn0-3/Cu1/Py3 was deposited by sputtering and a Hall bar pattern was then fabricated by photolithoghy. By change the thickness of IrMn layer and the measurement temperature, we found that antiferromagnetic and paramagnetic phase do not have significant influence on spin transport. The dampinglike torque and fieldlike torque decease when temperature goes down. We also use FMR to examine the spin absorption rate in //Cu3/Py10/Cu3/IrMn0-3/Cu3 sample. The thickness of IrMn layer does have influence on the spin absorption rate but without significant difference when the temperature is above and below Neel temperature. |
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G60.00184: Enhanced Intrinsic Spin Hall Effect of Bi Atoms on Ag(001) Surface Zhe Wang, Yizheng Wu, Ruqian Wu Spin Hall effect (SHE) of Bi atoms and impuritis on Ag(001) surface is investigated with density functional theory (DFT) calculations. A free standing Ag(001) layer has neglectable Spin Hall conductivity (SHC). However, we find that the addition of a small amount Bi atoms, either through adsorption of doping on the Ag(001) surface, the SHC may suddenly increase to larger than 2000/Ω.cm. Continous increase of Bi coververage after 1/9 monolayer causes gradual decrease of SHC, which becomes a constant value for Bi > 1 ML. Analysis of band structures and Berry curvatures indicate that the large SHC mainly results from the hybridzation of Ag s bands and Bi p bands. Further more, we find significant Rashba splitting in bands for Bi > 1 ML, which also contributes to the SHC. |
(Author Not Attending)
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G60.00185: Topological Spin Transport in Non-Collinear Antiferromagnets Fengjun Zhuo, Aurelien Manchon Non-collinear antiferromagnets have recently received significant attention with the prediction and experimental observation of anomalous Hall effect in Mn3X compounds [1]. In these materials, the anomalous transport is promoted by the coexistence of both non-collinear magnetic order and spin-orbit coupling. In the present work, we investigate the transport and optical properties of an antiferromagnet with non-trivial magnetic configuration in the absence of spin-orbit coupling. The model system we consider consists in a two-dimensional 3Q antiferromagnet with a texture similar to the one predicted by Kurz et al. [2] on Mn/Cu(111) interfaces. Building a minimal tight-binding model and exploiting Kubo formula, we computed the spin transport properties of the system and demonstrate that the non-trivial magnetic texture leads to topological anomalous Hall effect, as well as topological torques and damping enabling the electrical manipulation of the structure. We also show that in spite of the absence of spin-orbit coupling, this class of materials is also optically active. |
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G60.00186: Abstract Withdrawn
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G60.00187: Direct Measurement of the Static and Transient Magneto-Optical Permittivity of Cobalt Across the Entire M-edge in a Reflection Geometry by Use of Polarization Scanning Adam Blonsky, Dmitriy Zusin, Phoebe Tengdin, Maithreyi Gopalakrishnan, Christian Gentry, Michael Gerrity, Justin Shaw, Hans Nembach, Thomas Silva, Peter Oppeneer, Henry Kapteyn, Margaret Murnane The microscopic state of a magnetic material is characterized by its resonant magneto-optical response through the off-diagonal dielectric tensor component $\epsilon_{xy}$. However, the measurement of the full complex $\epsilon_{xy}$ in the extreme ultraviolet region covering the M absorption edges of 3d ferromagnets is associated with multiple experimental challenges. We demonstrate a new technique to extract $\epsilon_{xy}$ simply by scanning the polarization angle of linearly polarized high harmonics to measure the magneto-optical asymmetry in reflection geometry. Because this technique is more practical to implement than previous approaches, we can directly measure the time evolution of $\epsilon_{xy}$ (t) during laser-induced demagnetization across the entire M2,3 absorption edge of cobalt with femtosecond resolution. For polycrystalline Co films on an insulating substrate, the changes in $\epsilon_{xy}$ are uniform throughout the spectrum. This result suggests that, for strong demagnetization, the ultrafast demagnetization response is primarily driven by magnon generation. |
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G60.00188: Inertia-driven switching of antiferromagnets via electrically induced Dzyaloshinskii-Moriya torque Beongki Cho, Taeheon Kim, Peter Gruenberg, Song Hee Han Antiferromagnetic insulator has attracted much attention as a promising material for future magnetic devices because of ultrafast, ultralow-dissipation properties. In these materials, precessional switching working on the picosecond time scale is known to occur through strict phase matching between Néel orders l = (s1+s2)/2 and driving torques. Here, we report, as being distinct from original switching process, a switching scenario by using the direct coupling of electric field with Dzyaloshinskii-Moriya (DM) interaction in the centrosymmetric system. Using antiferromagnetic pendulum model, the temporal DM interaction that is induced by pulsed electric field is found to work not only as magnetic torques, as like spin-orbit torque or magnetic field, but also as magnetic potential that limits l’s activity in a given system. Thus, we demonstrate that appropriate control of DM vector determines switching efficiency. Our finding is used widely and necessary for modern electronics as ultrafast electrical manipulation in magnetic system. |
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G60.00189: Intrinsic magnetic effects in LaO0.5F0.5BiS2 from magnetic susceptibility and NMR measurements Silverio Delgado, Shrishti Yadav, Lei Shu, Oscar Bernal We present magnetic susceptibility and NMR data in LaO0.5F0.5BiS2 that suggest intrinsic magnetic effects in the normal state of this material. Magnetization measurements in temperatures from 2.7 K to 250 K and applied fields from -4 T to 4 T, and NMR experiments (carried out in similar temperature and field ranges) are compared to estimate the intrinsic magnetic contribution to the magnetic effects observed by both techniques. With the aid of Palladium (Pd) metal as a standard to assure that our equipment is operating accurately, our analysis of the data indicates that besides the expected contribution from paramagnetic impurities in the starting materials, there exists an intrinsic susceptibility whose origin is still not fully determined. The results clarify that we do observe an interesting magnetic phenomenon in LaO0.5F0.5BiS2, potentially related to a Rashba or a Dresselhaus effect that has been predicted for the parent compound. |
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G60.00190: Investigating Vortex Core Motion Driven by Thermal Gradients Sarah Deutsch, Jaclyn Schillinger, Michael Vogel, Christian Back, Tim Mewes, Claudia Mewes Magnetic vortices can be driven by spin polarized currents. The magnetization dynamics of such motion is described by the extended Landau-Lifshitz-Gilbert equation. In this work, we focus on spin polarized currents created by thermal gradients utilizing the Spin-Seebeck effect. Using full micromagnetic simulations we have studied the effects of different temperature gradients, lateral sample sizes, sample thicknesses, and damping parameters on the resulting vortex motion. Our results show that high temperature gradients are required to excite a measurable vortex core motion in a thin Permalloy sample. To increase the vortex motion, we also discuss the use of pulsed heating, which results in resonantly driven vortex motion. To further analyze our numerical results, we use an extended Thiele equation to analyze the gyroscopic motion of the thermally driven vortices. The good agreement between the full micromagnetics simulations and the semi-analytical solutions of the extended Thiele equation allows us to extend the analytical model to include magnonic effects and random temperature fluctuations. |
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G60.00191: Spectral Characteristics of Quasi-Equilibrium Magnon Gas Driven by Pure Spin Current Ryan Freeman, Boris Divinskiy, Vladislav Demidov, Sergei Urazhdin, Sergei Demokritov The discovery of the magnon Bose-Einstein condensate (BEC) in magnetic insulators driven by parametric pumping has spurred intense studies of thermodynamics of driven magnon gases. We utilized micro-focus Brillouin Light Spectroscopy to experimentally show that the spin current generated by the spin Hall effect can efficiently drive the magnon gas in a magnetic film into a quasi-equilibrium state well described by the Bose-Einstein statistics. |
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G60.00192: Polar Angle Dependence of interfacial Dzyaloshinskii-Moriya Interaction Woo-Yeong Kim, Hyung-Keun Gweon, Dae-Yun Kim, Hyeok-Cheol Choi, Min-ho Park, Yong-Keun Park, Sang-Ho Lim, Sug-Bong Choe, Chun-Yeol You, Kyung-Jin Lee The broken inversion symmetry combined with large spin-orbit coupling at the interface between heavy metal and ferromagnet gives rise to the antisymmetric exchange interaction, namely the interfacial Dzyaloshinskii-Moriya (iDM) interaction [1, 2]. In the presence of iDM interaction, spin-wave amplitudes and frequencies become asymmetric with respect to the spin-wave propagation direction [3]. In this work, we investigate the angular dependence of iDM interaction using Brillouin Light Scattering (BLS) [4]. We found that the magnitude of iDM shows weak polar angle dependence in Pt/Co/MgO structure. The magnitude of iDM is smaller when the magnetization is perpendicular than the magnetization is in-plane. |
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G60.00193: 55Mn and 27Al NMR investigation of YMn4Al8 single crystals Moohee Lee, Kihyeok Kang, Beongki Cho 55Mn and 27Al Nuclear magnetic resonance (NMR) measurements are performed on a single crystal of YMn4Al8 at 8 T down to 4 K. The NMR spectrum, Knight shift, linewidth, spin–lattice relaxation rate 1/T1, and spin–spin relaxation rate 1/T2 are measured as a function of temperature for the c-axis parallel and perpendicular to the magnetic field. The 55Mn NMR spectrum exhibits five broad satellites due to nuclear quadrupole interaction for a nuclear spin of I = 5/2. The 27Al NMR spectrum exhibits two different sites, Al-A and Al-B, with five satellites for each site due to nuclear quadrupole interaction for I = 5/2. Based on the broader linewidths of the Al-B spectra, the Al-B site turns out to be closer to the Mn 3d electrons. The local electronic structures at the Mn and Al sites measured by NMR are almost isotropic for the c-axis parallel and perpendicular to the magnetic field. The temperature dependence of the Knight shifts and the Korringa product 1/T1T, as well as the magnetic susceptibility, show a large decrease at low temperature, indicating the opening of a pseudo-gap in YMn4Al8. The Knight shift scales with the susceptibility, from which the hyperfine coupling constant is extracted and found to be 55A = −140 kOe/μB. |
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G60.00194: Mechanisms underlying the transition to the long-range spin glass state in the layered quasi-2D III-VI diluted magnetic semiconductor Ga1-xMnxS system Thomas Pekarek, Paul Edwards, Ian Manuel, Duncan Parker, Jason Haraldsen, I. Miotkowski, Anant Ramdas Magnetization data of single crystalline Ga1-xMnxS (x=0.09) were implemented in Density Functional Theory (DFT) analysis to characterize the complex exchange channels contributing to the spin-glass transition near Tc = 11.2 K. We examine the magnetization, electronic band structure, and density of states for manganese (Mn) doped gallium sulfide (GaS), which is a quasi-two-dimensional semiconductor. For our computer calculations, we start with undoped GaS and progressively add Mn atoms into randomly determined gallium (Ga) lattice sites up to x=0.18. We find the magnetization increases linearly with Mn doping. The presence of magnetic atoms produces impurity bands in the electronic structure. Examination of density of states shows that an increase in magnetic impurity bands seems to lead to the presence of a weak, but noticeable, spin polarization at the Fermi level. This indicates a possible half-metal state due to increased Mn doping. The presence of the impurity bands or half-metal state in Ga1-xMnxS provides a likely mechanism for the higher spin-glass transition temperature in Ga1-xMnxS compared with the substantially lower transition temperatures in related II-VI based systems such as Zn1-xMnxTe. |
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G60.00195: Domain Wall Dynamics and Ensuing Spin Pumping Driven by Current Pulses: Multiscale Time-dependent Quantum-classical Approach Marko Petrovic, Bogdan Popescu, Petr Plechac, Branislav Nikolic By combining the time-dependent nonequilibrium Green function formalism (NEGF) for the evolution of electronic density matrix, implemented [1] using an efficient algorithm which scales linearly in the number of time steps, with the classical Landau-Lifshitz-Gilbert equation (LLG) describing the motion of magnetic moments in ferromagnetic materials, we study the domain wall (DW) dynamics initiated by injection of ultrashort dc current pulses. Unlike the usually employed steady-state NEGF+LLG formalism for problems where dc charge current is injected, our time-dependent NEGF+LLG makes it possible to study injection of current pulses, as well as pumping of spin current into the electrodes due to the DW motion. We also demonstrate the limits of steady-state NEGF+LLG approach to study DW motion when dc current is injected, which naively assumes that electronic Hamiltonian commutes at different times. Thus, our approach opens new avenues for theoretical and computational optimization of the memory technologies [2] based on DW dynamics. |
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G60.00196: Characterization of the Spin Reorientation Transition in HoFe1-xVxO3 Stephen Tsui, Josefa Gregorio, Jesus Perez, Lorena Aguirre, Alejandro Zafra We investigate the effect of V doping on the spin reorientation phenomenon in the holmium-based orthoferrite HoFe1-xVxO3. Spin reorientation arises from a reconfiguration of the magnetic structure that leads to a rotation of the net magnetic moment between crystal axes. Polycrystalline samples were synthesized via solid state reaction and characterized by vibrating sample magnetometry. It is established that the spin reorientation occurs below 50 K in HoFeO3, and our results show that the transition temperature increases with V substitution. A probable mechanism is that the V doping interferes with the Fe-Fe magnetic interactions and allows the Ho-Fe interactions to dominate at higher temperature, which leads to the spin reorientation. |
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G60.00197: Tunable mode coupling in nano-contact spin torque oscillators Shulei Zhang, Ezio Iacocca, Olle Heinonen Recent experiments on spin-torque oscillators (STOs) have revealed interactions between multiple magnetodynamic modes, including mode coexistence, mode hopping, and temperature-driven crossover between modes. The initial multimode theory indicates that a linear coupling between several dominant modes, arising from the interaction of the subdynamic system with a magnon bath, plays an essential role in the generation of various multimode behaviors. In this work [1], we derive a set of rate equations to describe the dynamics of coupled magnetodynamic modes in a nanocontact STO, and analyze the dependence of the coupled dynamic behaviors of modes on various experimental conditions. For a minimal two-mode system, we further map the energy and phase difference of the two modes onto a 2D phase space and demonstrate in the phase portraits how the manifolds of periodic orbits and fixed points vary with external magnetic field and temperature. |
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G60.00198: Modulation of Voltage-Controlled Magnetic Anisotropy through Interface Engineering in FeCo/MgO Heterostructures Malcolm Jackson, Nicholas Kioussis Recent experiments have reported a large modulation of voltage-controlled magnetic anisotropy in Cr/Fe/MgO interfaces which arises from the presence of Cr atoms in the proximity of the Fe/MgO interface. Using ab initio density-functional theory calculations we have investigated the modulation of magnetic anisotropy in FeCo/MgO interfaces through controlled doping of Cr into the FeCo-MgO interface. The calculations reveal that the antiferromagnetic ordering induced by Cr decreases the magnetic anisotropy energy with increasing Cr concentration at the interface. We will present results of the effect of strain and electric field on the atom-resolved spin-orbit-coupling energies and k-resolved magnetic anisotropy to shed light on the underlying mechanism of the Cr alloying. |
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G60.00199: Influence of Grain Boundary on Coercivity in Rare-earth Permanent Magnet with Grain Surface Defects Rui Li, Hongrui Zhang, Kaiming Qiao, Fengxia Hu, Jirong Sun, Baogen Shen Coercivity (Hcj) microstructure-sensitive characteristic of Nd-Fe-B or Sm-Co magnet results in their complex and rigorous fabrication process. To improve Hcj by optimizing microstructure in magnets has been researched as a hot topic. Micromagnetic simulations (MS) have successfully clarified the factors affecting Hcj, such as grain size, grain defect, grain boundary (BG) and disorientation. But few studies have focused on a collective effect of above factors while the real magnets involve many unfavorable factors to Hcj. |
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G60.00200: Computational discovery of permanent magnet materials Durga Paudyal The first criteria for permanent magnetic material design is hexagonal and tetragonal structures which allow magnetic moments to align along the anisotropic crystal-axis. The non-equivalent crystal sites play a key role in determining the permanent magnet properties. Advanced density functional calculations incorporating electron-correlation and spin-orbit coupling show highest magnetic anisotropy contributed by R-1a (rare earth) site due to the crystal-field split 4f-states followed by the R centered T-2c (transition-element) ring sandwiched by T-3g in hexagonal RT5. The split 4f-states and the formation of T-2c 3d and R-1a 5d density of states peaks at the Fermi level are the origins of the maximum anisotropy. Calculations indicate that Co sites can be substituted by Fe to enhance the magnetic moment in SmCo5. Replacing Sm by Ce indeed shows c-axis anisotropy. Further engineering CeCo5 with Cu substitution shows enhanced magnetic anisotropy without significant reduction in the magnetic moment. One third of Ce sites substitution in CeCo5 by Co derives Ce2Co17 to hexagonal. |
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G60.00201: The role of crystal structure on magnetocrystalline anisotropy in non-cubic YCo5 and ZrCo5 compounds Masahiro Sakurai, James Chelikowsky, Shunqing Wu, Xin Zhao, Manh Cuong Nguyen, Cai-Zhuang Wang, Kai-Ming Ho We perform first-principles calculations based on plane-wave and real-space implementations of pseudopotential density-functional theory to investigate the magnetic properties of seven non-cubic YCo5 and ZrCo5 compounds including experimentally observed and theoretically predicted structures. By examining the impact of crystal structure on the total magnetic moment and magnetocrystalline anisotropy constant, we find that both cannot be simultaneously enhanced in YCo5 compounds. By substituting a rare-earth (RE) element of Y with Zr, a relatively abundant element, we can achieve a large magnetic anisotropy with a moderate total magnetic moment in a RE-free Co-rich compound. |
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G60.00202: On the Synthesis and Physical Properties of PVDF Nanofibers Loaded with Maghemite Dorina Chipara, Chamath Dannagoda, Santos Garcia, Karen Lozano, Maxim Sumets, Ion Morjan, Karen Martirosyan, Mircea Chipara Nanoparticles of maghemite have been synthesized by the laser pyrolysis of a mixture of iron pentacarbonyl, air, and ethylene, where the air was used as oxidizer and ethylene as a sensitizer. Electron microscopy, X-Ray spectra, and magnetic measurements have been used to characterize the as obtained nanoparticles. Nanocomposite nanofibers of PVDF loaded with various amounts of maghemite nanoparticles have been obtained by force spinning. The polymeric matrix (polyvinylidene fluoride) has been dissolved into a 50:50 mixture of acetone and dimethylformamide, at room temperature. The magnetic nanoparticles were added to this solution and the mixture was homogenized by high power sonication for 1 hour. The obtained solution was then force spun, at various rates, ranging from 1000 to 10,000 rotations/minute. Electron microscopy was used to assess the size distribution and shape of nanoparticles and of the nanofibers. Elemental analysis confirmed the presence of the nanoparticles within the nanofibers. The crystalline structure of the polymeric matrix and of nanoparticles was determined by X-Ray analysis. Additional Raman and magnetic measurements (hysteresis, field-cooled, and the zero-field-cooled measurements) are scheduled. |
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G60.00203: Discretized excitation spectra by magnon confinement in quasi S=1 spin-chain systems Takafumi Suzuki, Sei-ichiro Suga Quantized excitation spectra below the Neel temperature have been observed in recent inelastic neutron scattering measurements on (Ba/Sr) Co2V2O8 [1-3]. Interestingly, negative zeros of the Airy functions (NZAF) well explain the energy dependence of peak positions in the spectra. Since the effective model for these compounds is considered to be S=1/2 antiferromagnetic Ising-like XXZ chains, two spinons in the excitation continuum can be confined by interchain couplings and thus, the spectra become discretized [4]. In this study, we focus on the S=1 spin chains that shows excitation continuum originated by magnons and investigate the possibility of discretization by the interchain couplings. We calculate dynamical spin structure factors by employing iTEBD method. From the numerical results, we find that the magnon continuum in the Haldane chain also shows the discretization. The peak position is explained by the NZAF only if the system is placed at the Ising limit, where the single ion anisotropy is quite strong in contrast to the Heisenberg interaction. [1]S. Kimura, et al., PRL 99, 087602 (2007). [2]Z. Wang, et al., PRB 91, 140404(R) (2015). [3]B. Grenier, et al., PRL 114, 017201 (2015). [4]H. Shiba, Prog. Theor. Phys. 64, 466 (1980). |
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G60.00204: Magnetic Behavior of a High Entropy Oxide Tahereh Afsharvosoughi, David Crandles High entropy oxides are a new group of materials that have attracted attention because of interesting properties and potential applications. Previous workers have shown that equimolar mixtures of five binary oxides undergo a reversible transformation from single fcc phase material when sintered at high temperature (1000 oC) to multiphase material when sintered at 700 oC and back to single phase material when fired for a second time at 1000 oC. Using XRD, we have confirmed the entropy-driven reversible structural transition in equimolar mixtures of MgO, CuO, ZnO, NiO and CoO. However, reversibility was not found for magnetic properties. The field-cooled/ zero-field-cooled response was measured for a sample sintered at 700 oC which showed paramagnetic behaviour. When this sample was sintered at 1000 oC - when it was single phase fcc - the sample was antiferromagnetic with transition temperature around 110 K. But when the sample was forced to become multiphase by sintering again at 700 oC the overall magnetic behaviour was still antiferromagnetic. |
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G60.00205: Extending the Magnetic Deformation Proxy to Disordered Systems Christina Garcia, Joshua Bocarsly, Ram Seshadri Identifying better magnetocaloric materials is a necessary step in the advancement of magnetic refrigeration technology. The material property which distinguishes a promising candidate is a large entropy change upon isothermal application of a magnetic field (ΔSM). The magnetic deformation, ΣM, is a computational proxy which compares the relaxed structures of a composition with and without spin polarization included in the density functional theory (DFT) framework, and it has been shown to correlate well with experimental magnetic entropy changes. In this study, we extend the magnetic deformation proxy to systems which have a degree of configurational disorder which cannot be encapsulated computationally by a single unit cell. Through generation of supercells, we scan relevant ranges of x for the known magnetocalorics MnFe1-xCoxGe and (MnCoGe)1-x(NiCoGe)x. We show that trends of ΣM vs. x match well with experimentally determined ΔSM vs. x and suggest how to apply the computational proxy to other disordered systems. |
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G60.00206: Contrasting antiferromagnetic, spin-glass and magnetic glass states in the double perovskite Sr2-xLaxFeCoO6 Pradheesh R, Haripriya G. R., Kumar C. M. N., Luis Martinez, Christian Saiz, Srinivasa Rao, Pascal Manuel, Anatoliy Senyshyn, Tapan Chatterji, Sankaranarayanan V, Sethupathi K, Harikrishnan Nair The magnetism of the double perovskite Sr2-xLaxFeCoO6 (x = 0, 1, 2) strongly depends on the type of atom at the Sr-site and on the disorder at the Fe/Co sites. In this work, by employing a combination of magnetometry, neutron scattering and electron paramagnetic resonance spectroscopy, we demonstrate that as the content of La that replaces the Sr changes, the disorder and subsequently, the magnetism of Sr2-xLaxFeCoO6 transforms from a canonical spin glass (for x = 0) to a magnetic glass (for x = 1) and further, to a long-range ordered antiferromagnet (for x = 2). The magnetism in Sr2FeCoO6 manifests through a spin freezing at Tg ≈ 75 K, with features resembling a canonical spin glass. In the case of SrLaFeCoO6, strong evidence of diffuse magnetic scattering is present up to 300 K suggesting dominant short-range spin correlations at room temperature. Though two magnetic anomalies occur at Ta1 ≈ 75 K and Ta1 ≈ 250 K in this compound, no long-range magnetic order is established down to 2 K. In striking contrast to these two compounds, La2FeCoO6 has a long-range ordered magnetic state with a TN ≈ 350 K. Protocols of cooling-and-heating-under-unequal-fields clearly map out the non-equilibrium magnetization dynamics. |
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G60.00207: Comparison of magnetic behavior in nanostructured and crystalline forms of an intercalated dichalcogenide Paul Shand, Jake Parks, Michael Kuntz, Tim Kidd, Laura Strauss, Jesse Choe, Emilia Morosan We have made temperature- and field-dependent dc magnetization and ac susceptibility measurements on polycrystalline Mn-intercalated TaS2 (MnxTaS2) for concentrations x of Mn in the range 0.15 ≤ x ≤ 0.25. This magnetic behavior was compared with previously reported results for nanostructured MnxTaS2 with 0.15 ≤ x ≤ 0.24. The crystalline samples exhibited a paramagnetic to ferromagnetic (PM to FM) transition even for the lowest Mn concentration investigated (x = 0.15). The Curie temperature exhibited a peak as x decreased. This non-monotonic behavior is consistent with the RKKY interaction. The nanostructured material exhibited cluster-glass behavior at the lowest concentrations (x ~ 0.15) and a PM to FM transition at higher x values. For x = 0.24, nanostructured MnxTaS2 is a re-entrant cluster glass. Scaling of the ac susceptibility for the crystalline samples yielded a gap exponent Δ = γ + β slightly greater than 2 whereas corresponding values for nano-MnxTaS2 were anomalously high (> 4). The differences in behavior are attributed to clustering effects attendant to the spatial distribution of Mn ions in the two morphologies. |
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G60.00208: Fixed Magnetic Skyrmion Based Resonate and Fire Neurons Md Ali Azam, Dhritiman Bhattacharya, Damien Querlioz, Jayasimha Atulasimha The membrane potential of resonate and fire neurons oscillate in a subthreshold damped fashion and fire when excited by an input frequency that nearly equals to their Eigen frequency[1]. We model such neurons by utilizing the magnetization dynamics of a fixed magnetic skyrmion in the free layer of a magnetic tunnel junction. To realize firing of a neuron, we propose to employ voltage generated strain or voltage control of magnetic anisotropy as input spike which modulates the magnetic anisotropy. This evokes continual expansion and shrinkage motion (i.e. breathing) of the skyrmion that mimics the subthreshold oscillation. Any subsequent input pulse having interval equal to the breathing period drives this motion into resonance. An annular electrode is used to identify if a threshold value is surpassed which is assumed as firing of the neuron. By rigorous micromagnetic simulation, we investigate the interspike timing dependence and response to different excitatory and inhibitory incoming input pulse such as doublet, triplet and bursts. |
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G60.00209: Treating schizophrenic patients, using high precision coils. John Germick, Youssif Alkheder, Priyam Rastogi, R. L. Hadimani, David Jiles Transcranial Magnetic Stimulation (TMS) has been used to treat many psychiatric and neurological disorders. This non-invasive treatment method is FDA approved to treat depression and much research has been done to use the treatment on other disorders, one such disorder is schizophrenia. Unfortunately, minimal research has been done in this area because of the inherent complexity and diverse array of symptoms. The most prevalent and potentially treatable symptom experienced by schizophrenic patients are persistent auditory hallucinations. The primary auditory cortex is one region of the brain responsible for the realization of such hallucinations. However, this region is relatively small, in order to stimulate this area without overstimulating surrounding areas, a higher precision coil than the commercial “Figure-of-Eight coil” (FOE) is required. The authors have performed Finite Element simulations with both the FOE and the novel Quadruple Butterfly Coil (QBC) on heterogeneous head models of both healthy and schizophrenic individuals. Our findings show that the QBC focused on the primary auditory cortex stimulates significantly of the brain cortex than the FOE. This result provides an alternative coil that could be used in order to stimulate smaller regions of the brain. |
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G60.00210: Magnonic Interferometric Switch for Multi-Valued Logic Circuits Alexander Khitun, Michael Balinskiy, Alexander Kozhevnikov, Yuri Khivintsev, Tonmoy Bhowmick, David Gutierrez, Howard Chiang, Galina Dudko, Yuri Filimonov, Guanxiong Liu, Chenglong Jiang, Alexander Balandin, Roger Lake We investigated a possible use of the magnonic interferometric switches in multi-valued logic circuits. The switch is a three-terminal device consisting of two spin channels where input, control, and output signals are spin waves. Signal modulation is achieved via the interference between the source and gate spin waves. We report experimental data on a micrometer scale prototype based on Y3Fe2(FeO4)3 structure. The On/Off ratio of the prototype exceeds 36 dB at room temperature. The utilization of spin wave interference as a switching mechanism makes it possible to build nanometer-scale logic gates, and minimize energy per operation, which is limited only by the noise margin. The utilization of phase in addition to amplitude for information encoding offers an innovative route towards multi-state logic circuits. We describe possible implementation of the three-value logic circuits based on the magnonic interferometric switches. The advantages and shortcomings inherent in interferometric switches are also discussed. |
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G60.00211: Spin wave logic devices with positive feedback Alexander Khitun, Michael Balinskiy, Howard Chiang, Sergey Rumyantsev, Alexander Balandin Spin wave logic devices is a type of magnetic devices that utilize spin waves for data transfer and processing. A fast amplitude damping is a major drawback inherent in the spin wave devices. We propose a combination of the spin wave logic devices with an auto-oscillatory circuit. This combination allows us to compensate the spin wave losses, and to significantly improve the output characteristics by providing the gain and suppressing the amplitude noise. We present experimental data showing the operation of the prototype circuit implemented with the Y3Fe2(FeO4)3 structure. The on/off ratio of the device exceeds 40 dB, and it is limited only by the non-linear decay processes in the magnetic film. The noise level is -110 dB/Hz at the frequency f=10 Hz. The physical limitations and technological constraints of the proposed approach will also be discussed. |
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G60.00212: Abstract Withdrawn
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G60.00213: Experimental Verification of Transcranial Magnetic Stimulation Using Newly Developed Brain Phantom Hamzah Magsood, Ahmed Elgendy, R. L. Hadimani Transcranial Magnetic Stimulation (TMS) is a promising and non-invasive technique for diagnostics and treatments of variousneurological diseases [1]–[3]. However, the lack of realistic and anatomical brain phantoms made the examination of induced electric fields on the brain tissues to be not well established and measured. We have developed a 3-D anatomically realistic brain phantom that can mimics the electrical conduction the brain. To produce the phantom, we 3-D printed shells for each tissue layer of the brain. Brain tissues are divided mainly into cerebrospinal fluid (CSF), white matter (WM), grey matter (GM), ventricles, and cerebellum. These layers are made into shells and after 3D printing them, they are filled with a conductive material multi walled carbon nanotubes (MWCNT) that is capable of mimicking the electrical conductive properties of different brain tissues. The phantom will be examined under different TMS parameters and compared with FEM modelling of induced electric and magnetic fields. Microelectrodes will be placed at different locations/depths on the phantom to measure the current I and resistance Ω. Since the phantom exhibits same electrical properties of the brain, close readings to actual TMS procedures is expected to be achieved. |
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G60.00214: Demonstration of low-field NMR detection in static fields produced by unilateral magnets Neelam Prabhu Gaunkar, Mani Mina, David Jiles Detection of NMR signals in low-fields produced by unilateral magnets would find large applications in portable medical diagnostics. However, use of low static magnetic fields for NMR detection remains a challenge due to low signal to noise ratio (SNR), lower splitting and lesser number of spin transitions between energy levels. Often techniques such as hyperpolarization, signal processing and pulse-sequencing are used to overcome such limitations. Besides these methods, it is also possible to tune the magnetic field strength and distribution around the magnets to achieve improved SNR. One way is to locate regions of uniform magnetic field outside hollow ring magnets. Typically referred to as saddle points, in these regions the magnetic fields are relatively invariant. Test samples can then be placed at these locations, and on application of precise pulsed magnetic fields, NMR signals under low uniform fields may be obtained. Therefore, in this work, finite element calculations are used to determine the location of saddle points and correspondingly detected NMR signals for chemical species such as 1H are recorded. |
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G60.00215: Use of passive magnetic material of different shapes for Transcranial Magnetic Stimulation Priyam Rastogi, Bowen Zhang, Yalun Tang, Erik Lee, R. L. Hadimani, David Jiles Transcranial Magnetic Stimulation (TMS) is an FDA approved treatment for the Major Depressive Disorder. It is a painless, non-invasive method which also have therapeutic effects on several other neurological disorders. TMS utilizes a time varying magnetic field to induce electric field in the brain which causes depolarization of the neurons. Quadruple Butterfly Coil (QBC) is a focused TMS coil which has 25% less volume of stimulation in comparison to commercial Figure-8 coil, with comparable maximum electric field value. Passive magnetic shields of different shapes, permeability, and position have been explored along with QBC to further improve the focality. The results with the passive shields along with the QBC has been shown with the help of a heterogeneous head model at two positions: Vertex and Dorsolateral Prefrontal Cortex. It has been found that there is an improvement in the ratio of maximum electric field at the scalp to the maximum electric field at the brain. Although, no difference has been determined in the volume of stimulation, when permeability, angle or position of the passive magnetic material had been varied. |
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G60.00216: Strongly Coupled Modes of M and H for perpendicular resonance Wayne Saslow, Chen Sun We apply the equations for M and H to study the two doubly-degenerate coupled modes of M and H for a semi-infinite ferromagnet, conductor or insulator, magnetized normal to the plane (perpendicular resonance), for wavevector normal to the plane. With dimensionless damping constant α and dimensionless transverse susceptibility χ⊥=M0/He (He≡Happ−M0), an analytic expression for the eigenmodes shows that for perturbation theory to apply the condition α >> χ⊥ must hold. This is violated in the ferromagnetic regime, so perturbation theory does not apply there. This generalizes numerical results of Ament and Rado for parallel resonance. Emphasizing the conductor permalloy, we study the eigenvalues and eigenmodes, as well as the dissipation rate due to absorption both from the total effective field (including, for the first time, the contribution of the non-uniform exchange energy term) and from Joule heating. Using these modes we then apply, for a semi-infinite ferromagnet, a range of boundary conditions (i.e. surface anisotropies) on M⊥ to find the reflection coefficient R and reflectivity |R|2. We show that the absorption is given, not by the imaginary part of the susceptibility, but of an effective susceptibility that includes the effect of the non-uniform exchange coefficient A. |
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G60.00217: Relationship between Transcranial Magnetic Stimulation intensity and the growth rate of N27 Dopaminergic Neurons in vitro Xiaojing Zhong, David Jiles Transcranial Magnetic Stimulation (TMS) is a non-invasive neuromodulation technique for the treatment of many neurological disorders. In 2008, TMS has been approved as a treatment for major depressive disorders by the US Food and Drug Administration (FDA). A time-varying magnetic field induces an electric field in the brain, therefore TMS has the ability to activate neurons in vivo. However, the effects of the magnetic fields on neurons in cell culture have not been investigated adequately. It has been found that transcranial magnetic stimulation promotes the proliferation of N27 cells in vitro. Based on these results, we investigated the effects of the magnetic fields generated by a biphasic stimulator with an air-cooled 70 mm double coil on a rat dopaminergic neurons cell line (N27) to explore the relationship between the stimulation intensity and the growth rate of N27 cells in vitro. The results of experiments showed that the difference in cell numbers between treatment group and control group is positively related to the stimulation intensity. It means the effects of magnetic stimulation on the proliferation of N27 cells is positively related to the magnetic field intensity. |
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G60.00218: Direct observation of multivalent states and 4 f → 3d charge transfer in Ce-doped yttrium iron garnet thin films Hari Babu Vasili, Blai Casals, Rafael Cichelero, Julian Geshev, Pierluigi Gargiani, Manuel Valvidares, Javier Herrero-Martín, Eric Pellegrin, Josep Fontcuberta, Gervasi Herranz Due to their large magneto-optic responses, rare earth-doped yttrium iron garnets, Y3Fe5O12 (YIG), are highly regarded for their application potential in photonics and magnonics. Here, we consider the case of Ce-doped YIG (Ce-YIG), in which substitutional Ce3+ ions are expected to be magnetic because of their 4f1 ground state. To investigate the impact of Ce-doping on the magnetism and electronic properties of the YIG parent compound, we exploited synchrotron x-ray spectroscopies. Using these element and site- specific spectroscopies, we demonstrate the emergence of an electron charge transfer from Ce 4f states specifically towards Fe 3d states at the tetrahedral sites of the YIG structure. As a consequence of the perturbation of the cation electronic states, the site-specific (Ce and Fe) sublattice magnetizations are disturbed in such a way that their respective magnetization hysteretis curves show atypical signatures, deviating from conventional magnetic hysteretic behavior. Our study establishes a step forward in the comprehension of the fundamental physical processes caused by rare-earth doping regarding YIG electronic and magnetic properties that, as aforementioned, is a prerequisite to further optimize and tailor the optical properties of these important materials. |
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G60.00219: Synthesis and evolution of magnetic properties on Sr1-xKxCrOz x= 0.0 – 0.5 system. Elizabeth Chavira, Gustavo Antonio Jiménez, Jesus Arenas, Adriana Tejeda, Karla Eriseth Reyes Morales, Jorge Barreto The layered oxides originated from the perovskite structure create an enormous family of compounds that produces a very rich physics. For the case of 3d elements, this family was at the beginning of the discovery of high Tc superconductivity in the oxides or giant magnetoresistance in manganates. A layer structure always plays, an essential role. We have started a study of the different members of the Ruddlesden-Popper series based on chromium. We report the synthesis and their magnetic behaviour on Sr1-xKxCrOz x= 0.0 – 0.5 system (SKCO). The technique of manufacture used was solid-state reaction. We focus here on the SKCO rhombohedra unit cell (PDF 00-029-1047), and its magnetic characterization. The TG analysis gives the idea of the reaction temperatures. By solid-state reaction we obtain SKCO Primitive rhombohedra structure that reaction stars from 723 K. SKCO rhombohedra is an insulator with an antiferromagnetic (AFM) transition at TN= 280 K. Only when x= 0.10 we observe the introduction of K in the crystal structure at room temperature. The highest reaction temperature used was 933 K. |
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G60.00220: Imaging Magnetic Dynamics with In Situ and Ultrafast Lorentz Transmission Electron Microscopy Tyler Harvey, Nara Rubiano da Silva, Marcel Möller, John Gaida, Armin Feist, Sascha Schäfer, Claus Ropers Magnetic microscopy based on the magneto-optic Kerr effect (MOKE) can offer femtosecond temporal resolution of magnetic dynamics, but limited spatial resolution. On the other hand, a spatial resolution on the order of ten nanometers is possible when imaging with X-ray magnetic circular dichroism (XMCD), but temporal resolution is limited to ten picoseconds at best at synchroton beamlines. Lorentz transmission electron microscopy (LTEM) offers spatial resolution comparable to XMCD, when combined with a pulsed electron source [1], a temporal resolution comparable to time-resolved MOKE [2]. Whereas MOKE and XMCD are sensitive to magnetization, and are typically used to image the out-of-plane component, LTEM is sensitive to in-plane magnetic fields. With options for in situ sample excitation including optical pulses, alternating currents, and external magnetic fields, LTEM is an ideal platform to probe magnetic dynamics. We present experiments on ferromagnetic nanostructures and skyrmions to illustrate the capabilities. |
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G60.00221: Giant Paramagnetism and Ferromagnetism of Copper Nanoparticles in a Carbon Matrix Medhanie Estiphanos, Eduard Sharoyan, Aram Manukyan, Harutyun Gyulasaryan, Oscar Bernal, Armen Kocharian Solid-phase pyrolysis of polycrystalline copper phthalocyanine (CuPc, Pc=C32N8H16) yielded Cu nanoparticles encapsulated in a graphite-like carbon shell - Cu@C nanocomposites. Magnetic measurements in series of average sizes of copper nanoparticles in the range of 5-40 nm were conducted by a vibrational magnetometer in the temperature range 10-300 K and magnetic field up to the 60 kOe. Giant paramagnetism, apparently due to conduction electrons with ballistic mean free path (large orbital magnetism) was detected for nanoparticles with small average size of Cu nanoparticles, 5-7 nm. At temperature T= 10K the value of the specific susceptibility is of order 1.5×10-4 emu/gOe. Ferromagnetism (Ms ≈ 0.5 emu/gCu) was also detected in Cu@C nanocomposites from helium up to room temperature. |
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G60.00222: Three-Dimensional Imaging of Stray Magnetic Field with Nitrogen-Vacancy Centers in Diamond Dwi Prananto, Daisuke Kikuchi, Kunitaka Hayashi, Toshu An Diamond with nitrogen-vacancy (NV) center is a material system with paramagnetic centers that are very sensitive to magnetic field perturbation. This characteristic makes diamond NV center an excellent sensor for high sensitivity and high-resolution magnetometry application. Thanks to the Zeeman effect, the splitting of its spin-1 degeneracy under magnetic field perturbation is responsible for its magnetic sensing ability. The energy level lifting of the NV spins is detectable through its spin-selective fluorescence. The vector of external magnetic field in the proximity of the NV spins can be inferred from the optically detected resonance spectrum. Here we present three-dimensional stray magnetic field vector imaging from a magnetic structure using an ensemble of NV spins in a (001) oriented diamond. The optically detected magnetic resonance spectrum is obtained by the continuous illumination of 532 nm laser and microwave frequency sweep over the resonance frequency of the electron spins. By interrogating NV spins around the magnetic structure, variations of resonance spectrum are acquired and local 3-dimensional vector magnetic field is recovered. The sensitivity of 2.5 µTHz-1/2 is achieved from this diamond magnetometry with a spatial resolution of about 1 µm. |
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G60.00223: Local magnetic behavior of EuB6 with Magneto Optic Imaging technique Dibya Sivananda, Md. Arif Ali, Pintu Das, Jens Mueller, Zachary Fisk, Satyajit Banerjee EuB6 is a low carrier density ferromagnetic semi-metal which is a convenient system to study nanoscale phase separation between conducting ferromagnetic and insulating paramagnetic domains. EuB6 undergoes magnetic ordering through stepwise transformation, with two anomalous features in the range of Tc1~15 to 16 K and Tc2 ~ 12 to 14 K and shows a large negative magnetoresistance at Tc1. We perform highly sensitive Magneto-Optic Imaging of a EuB6 sample which unlike other methods can image local magnetic fields on the surface of a sample. Polaronic magnetic domains in a single crystal of EuB6 has been successfully imaged through our technique. We identify different regimes related to nucleation of magnetic polarons, the temperature regimes where the polarons completely coalesce and where they finally join up to enter into a state with a long-range magnetic order. These have been identified as T*, T*c1 and Tc2. We investigate the field dependent behavior of T*, T*c1, Tc2 and determine a phase diagram to identify their behavior with field. The above transformation is shown to have features of a critical like phenomena. We also observe an increase in noise as we cross T*c1 and Tc2 which is suppressed at Tc2 when an external field is applied. |
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G60.00224: Effect of Nb concentration on the magnetotransport properties and the spin-orbit coupling strength in Nb-doped SrTiO3 epitaxial thin films Suyoun Lee, Seong Won Cho, Inhak Lee, Milim Lee, Sungmin Woo, Kanghoon Yim, Seungwu Han, Woo Seok Choi Several oxides have attracted much interest in spintronics due to unusual properties originating from the correlated orbital and spin degrees of freedom. One missing part in oxide spintronics is a good spin channel featured by strong spin-orbit coupling (SOC) which enables an efficient control of the electron’s spin. Motivated by a recent finding of the strong SOC in a heavily-doped Sr(Nb0.2Ti0.8)O3 epitaxial film, we have systematically studied the dependence of the SOC strength on Nb concentration (nNb=2 ~ 20 at. %) by investigating the magnetotransport properties. We have found that the magnetoresistance (MR) is well described by the weak antilocalization (WAL) and the SOC strength increases with nNb. In addition, we have observed an anomalous behavior near 10 K in the SOC strength independent of nNb, which might be associated with the temperature dependent Landé g-factor. Furthermore, MR is found to be anisotropic for the intermediate doping regime (nNb=5 and 10 at. %) while being isotropic for the low and high doping regime (nNb =2, 15, and 20 at. %). The calculation of band structure shows this behavior is associated with the splitting of Nb-d bands by the crystal field and the change of the Fermi level with nNb. |
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G60.00225: Charge Doping and Quantum Monte Carlo of NiO Friederike Wrobel, Changhee Sohn, Hyeondeok Shin, Anouar Benali, Panchapakesan Ganesh, Olle Heinonen, Ho Nyung Lee, Anand Bhattacharya NiO is a widely studied model Mott insulator that orders antiferromagnetically below 520 K. The Ni spins align ferromagnetically within the (1,1,1) planes of the NaCl structure and antiferromagnetically between those planes. The transition temperature drops with Li doping and the system becomes first ferrimagnetic and later again antiferromagnetic with a Néel temperature of 9 K. Despite the intense study of NiO and other Mott insulators, the evolution of electronic correlations upon charge doping, which gives rise to a plethora of spectacular phenomena (including superconductivity in cuprates) is poorly understood to date. In a new effort, combining Quantum Monte Carlo (QMC) with thin film growth of charge-doped NiO, we address this question. We analyze the band gap with spectroscopic ellipsometry as a function of doping and strain and compare the results to QMC. This will lead to a better understanding of the electronic correlations that bring about charge or magnetic order or superconductivity. |
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G60.00226: Bulk spin Hall effect in topological insulator thin films Abhishek Banerjee, R Ganesan, PS Anil Kumar Spin current generation in topological insulators(TI) is usually attributed to the spin-momentum locking of topological surface states, where the direction of current fixes the direction of net spin-polarization. However, this mechanism cannot explain the relatively large spin currents observed in experiment. Recently, it has been proposed that the insulating, but topologically non-trivial bulk of a TI may produce large transverse spin currents through the bulk-spin Hall effect. This effect was first predicted in 2004[1], but never experimentally observed. In this work, we study magneto-transport in Bi2Se3 thin films in perpendicular and parallel magnetic fields as a function of sample thickness, disorder strength and temperature and reveal direct evidence for a transverse bulk current that electrically connects the top and bottom topological surface states. From this, we estimate the bulk spin Hall conductivity in our samples that closely matches with theoretical predictions. Our work constitutes the first experimental observation of the bulk spin Hall effect in TIs and paves the way towards designing highly efficient charge-to-spin converters using TIs.([1]. Phys. Rev. Lett. 93, 156804(2004)) |
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G60.00227: Generation and detection of dissipationless spin current in Si Paul Lou, Sandeep Kumar The generation and detection of spin current without ferromagnetic or exotic/scarce materials are two the biggest challenges for spintronics devices. In this study, we report a solution to the two problems of spin current generation and detection in Si. Using non-local measurement, we experimentally demonstrate the generation of helical dissipationless spin current using intrinsic spin-Hall effect. The intrinsic spin Hall effect is attributed to the site-inversion asymmetry in the diamond cubic lattice of Si. The spin to charge conversion in Si is insignificant due to weak spin-orbit coupling. For the efficient detection of spin current, we report spin to charge conversion at the MgO (1nm)/Si (2 µm) (p-doped and n-doped) thin film interface. Using x-ray photoemission spectroscopy, we determined that the interface consists of MgO/Mg/SiO2. The oxygen deficient interface leads to a two-dimensional electron system. The structure inversion asymmetry at the interface leads to Rashba spin orbit coupling and efficient spin to charge conversion observed in this work. The existence of spin current in Si is verified from coercivity reduction in Co/Pd multilayer from spin-orbit torque generated by spin current from Si. |
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G60.00228: M-plane GaN epifilms doped with Mn grown by PAMBE Li-Wei Tu, P. V. Wadekar, C. W. Chang, H. C. Huang, C. M. Cheng, M. Chou, W. C. Lai, J. K. Sheu, Q. Y. Chen Nonpolar m-plane gallium nitride (m-GaN) epifilms were grown on the substrate of m-plane sapphires using the plasma-assisted molecular beam epitaxy (PAMBE) system. One series was to vary the nitrogen plasma power to obtain a uni-phase epitaxial film and another was to vary the growth temperature to obtain a metal-free high-quality sample. The metal droplets started to appear when it was in the lower power range while the droplet size increased and the density reduced with reducing power. X-ray diffractometry revealed a uni-phase structure at lower power and a multi-phase structure at higher power. Further increase of the growth temperature removed the surface metal and improved the quality of the epitaxial film further. Strain analysis was performed through Raman spectroscopy and the result is explained by the lattice mismatch between the epifilm and the substrate. Transition metal manganese (Mn) doping into the m-GaN was explored for room temperature ferromagnetism. Magnetic measurements along with x-ray photoelectron spectroscopy and x-ray absorption spectroscopy were done. |
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G60.00229: ATOMIC, MOLECULAR AND OPTICAL (AMO) PHYSICS
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G60.00230: Measurement of the Kα doublets of Molybdenum Timothy Brady, William Alexander, Misganaw Getaneh In this measurement we determine the energy separation of the two characteristic x-ray emissions in the Kα doublet of Molybdenum using x-ray diffraction by a Lithium-Fluoride (Li-F) mono-crystal target. The two Kα lines are very close in energy and they appear as a single emission line in most x-ray spectrometry measurements. It requires use of high resolution equipment and looking at higher orders of diffraction interference for a long time to see clearly the separated Kα doublets, Kαlpha-1 (Kα1) and Kα1pha-2 (Kα2) un-ambiguously. It was necessary to do the measurement over a long time because the count rate of the scattered x-rays decreases significantly with increase in the order of interference. But at the same time lines separation shows better at higher orders of interference. According to our measurement the wavelength separation of the Kα doublets is: Δλ = (0.42 ± 0.13) pm. This is consistent with the literature value: Δλ = 0.43 pm. The corresponding energy separation of the two lines, according to this measurement is: ΔE = (0.104 ± 0.032) keV. |
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G60.00231: Raman scattering of MoS2 near gold nanoparticles Mojtaba Moazzezi, Yan Jiang, Usha Philipose, Yuri Rostevtsev The Raman scattering of molybdenum disulfide (MoS2) has been studied. In the presence of gold nanoparticles, strong modifications of Raman spectra have been observed. The Raman frequencies have been shifted and the line profiles are broadened. We developed a theoretical model to explain the observed features of the Raman scattering. The model take into account self-consistently the interaction of molecules with surface plasmonic waves excited in the gold nanoparticles, and it provides a qualitative agreement with the observed Raman spectra. We have demonstrated that the using gold nanoparticles can increase sensitivity of the technique, and potentially it has a broader range of application to both spectroscopy and microscopy. |
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G60.00232: Quantitative Phase Imaging with Incoherent Light Laura Solomon, Ziyi Zhu, Zhimin Shi Microscopy is a crucial in biological, biophysical, and cancer research. Biological samples are often quite transparent, which results in poor contrast ratio in the images from a conventional microscope. Phase Contrast Microscopy (PCM) converts the “invisible: phase information of the sample into the intensity of the images by shifting the relative phase of the different spatial frequency components. A quantitative phase imaging system, known as PRINT, has recently been developed using a laser source. However, the long coherent length of the light source introduces noises due to reflection/scattering from unwanted surfaces in the optical path. In this project, we focus on developing a PCM with the capability to quantitatively measure phase information of a sample using incoherent light. We simulate, construct, and calibrate a microscopy system, and use it to observe objects which are relevant for biophysics research. |
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G60.00233: Slow Thermalisation in the Quantum East Model Philip Crowley, Vadim Oganesyan, Andrew Green The kinetically constrained Quantum East Model has been found to exhibit characteristics of many body localization despite translational invariance. In this talk I show that constrained dynamics in quantum spin models can cause slowed or arrested thermalisation without disorder. This occurs when the evolution is dominated by dynamically frozen regions, and induces super-Arrhenius slow dynamics at low temperatures. In this regime the quantum model relaxes slower than its classical analogue, and has a strong susceptibility to disorder with low energy density states localising at weak disorder. |
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G60.00234: Topological Zak Phase in Strongly-Coupled LC Circuits Tal Goren, Kirill Plekhanov, Félicien Appas, Karyn Le Hur We show the emergence of topological Bogoliubov bosonic excitations in the relatively strong coupling limit of an LC (inductance-capacitance) one-dimensional quantum circuit. This dimerized chain model reveals a Z2 local symmetry as a result of the counter-rotating wave (pairing) terms. The topology is protected by the sub-lattice symmetry, represented by an anti-unitary transformation. The winding of the topological Zak phase across the Brillouin zone can be measured by a reflection measurement of (microwave) light. Our method probes bulk quantities and can be implemented even in small systems (∼10 unit cells). We also study the robustness of edge modes towards disorder. |
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G60.00235: Design and fabrication of ultra-coherent nanomechanical oscillators using phononic crystals and strain engineering Amir Ghadimi, Sergey Fedorov, Nils Johan Engelsen, Mohammad Bereyhi, Dalziel Wilson, Tobias Kippenberg Ultra-coherent mechanical oscillators are promising candidates for studying the quantum behavior of macroscopic objects. A necessary condition for such tests of quantum mechanics is to have sufficiently low dissipation to perform several coherent oscillations at. In high-stress Si3N4 thin films, so-called ‘dissipation dilution’—where the stiffness of the material is increased without added loss—enables anomalously high quality factors. |
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G60.00236: Swapping mechanical excitations in multi-mode optomechanics Vitaly Fedoseev, Matthew Weaver, Jose Luna, Sameer Sonar, Frank Buters, Kier Heeck, Wolfgang Löffler, Dirk Bouwmeester High displacement sensitivity of an optical cavity combined with effective quantum state transfer open up a possibility to study quantum mechanics on a macroscopic level. We study the interaction of the mechanical motion of a thin dielectric membrane with light in a rigid optical cavity in a "membrane in the middle setup". The membrane is partly reflective which effectively splits the cavity into to two cavities and gives rise to non-zero optomechanical coupling. The cavity is coupled to multiple vibrational modes of the membrane. Using two laser beams we show high efficiency energy transfer between modes of highly disparate frequencies which are otherwise not mechanically coupled. We also study theoretically another possibility which is state transfer between the modes using the stimulated Raman adiabatic passage technique (STIRAP) with the light cavity mode being the "dark" state. The ultimate goal of the state transfer in the quantum regime is to study macroscopic entanglement and decoherence models. |
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G60.00237: Measuring Plasmonic Dichroism with Electron Vortex Beams Cameron Johnson, Tyler Harvey, Benjamin McMorran Plasmonic circular dichroism has been demonstrated in clusters of metallic nanoparticles with chiral structure by measuring the difference in absorption spectra between right and left circularly polarized light, but is limited in the energy scales it can probe and spatial resolution it can achieve. Electron vortex beams, which carry quantized amounts of orbital angular momentum, can be realized in transmission electron microscopes. These vortex beams can probe excitation energies ranging from meV to keV and can achieve atomic resolution. Recently, simulations have shown that metallic nanoparticles with a chiral structure can exhibit a dichroic signal resolvable with electron energy loss spectroscopy when excited with right- and left-handed electron vortex beams analogous to the circular dichroism displayed with optical spectroscopies using polarized light. Here we present initial experimental results and further simulations showing intrinsic and extrinsic dichroism in chiral nanoparticle structures and their dependence on the amount of orbital angular momentum being transferred from electron vortex beams to plasmon modes. |
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G60.00238: A Technique for Measuring Decoherence through Mechanical Interference in Multimode Optomechanics Jose Luna, Matthew Weaver, Vitaly Fedoseev, Sameer Sonar, David Newsom, Kier Heeck, Wolfgang Löffler, Dirk Bouwmeester The process of quantum state swapping allows the preparation and control of hard-to-manipulate quantum systems through more manageable auxiliary systems. This is useful for the study of fundamental physics as it enables us to couple systems in disparate regimes and exploit the advantages of each. We propose an experiment in which a high-frequency resonator prepared in a single-phonon Fock state is coupled to a massive, low-frequency resonator with two-tone pi/2-pulses. Assuming the high-frequency resonator is well isolated from the environment, we can study decoherence of the massive resonator by monitoring the interference pattern in the phonon occupation of the two resonators. The proposed scheme is general and can be implemented in any system with two independently addressable modes. We present fabrication details of one implementation with trampoline resonators. In addition, we report microfabrication goals, challenges and techniques for a different implementation with thin membrane resonators. |
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G60.00239: Electronic zero-point fluctuation forces inside circuit components Ephraim Shahmoon, Ulf Leonhardt One of the most intriguing manifestations of quantum zero-point fluctuations are the van der Waals and Casimir forces, often associated with vacuum fluctuations of the electromagnetic field. Here we study generalized fluctuation potentials acting on internal degrees of freedom of components in electrical circuits. These electronic Casimir-like potentials are induced by the zero-point current fluctuations of any general conductive circuit. For realistic examples of an electromechanical capacitor and a superconducting qubit, our results reveal the possibility of tunable forces between the capacitor plates, or the level shifts of the qubit, respectively. Our analysis suggests an alternative route towards the exploration of Casimir-like fluctuation potentials, namely, by characterizing and measuring them as a function of parameters of the environment. |
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G60.00240: Cold-atom Quantum Simulation of Ultrafast Phenomena, Phasonic Spectroscopy, and Anyons Peter Dotti, Toshihiko Shimasaki, Ruwan Senaratne, Shankari Rajagopal, David Weld We present experiments using degenerate strontium atoms for the quantum emulation of ultrafast dynamics, quasiperiodic many-body systems, and anyonic modes in the Kitaev chain. Trapped atoms subjected to a time-varying force field are used to emulate the ultrafast dynamics of electrons or nuclei in a binding potential. This enables the study of attosecond or femtosecond phenomena in atoms or molecules exposed to the electric field of a pulsed laser. Separately, we study the dynamical response of atoms in a quasiperiodic bichromatic lattice to rapid modulation of the phason degree of freedom. Such excitations are typically frozen out due to strain in solid-state quasicrystals; these measurements thus represent a new spectroscopic probe of quasicrystals which is inaccessible to traditional experiments. Finally, we discuss a technique for cold-atom quantum emulation of the Kitaev chain Hamiltonian, with the goal of realizing a cold-atom system which features Majorana fermions with anyonic quantum statistics. |
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G60.00241: Light-cones and quantum caustics in quenched spin chains Wyatt Kirkby, Jesse Mumford, Duncan O'Dell We discuss the light-cone-like structures in spin chains following a quantum quench, and identify these stuctures as examples of quantum caustics. Specifically, we connect the light-cone to catastrophe theory and show that they arise from singularities in a gradient map due to coalescing saddles in a generating function, which in turn takes the form of an action. The identification of light-cones as catastrophes ensures structural stability and self-similarity scaling relations of both wave- and correlation functions, which asymptotically take the form of well-known diffraction integrals. We present a quench in the transverse-field Ising model as an example, and in addition to the features mentioned above, we demonstrate the existence of a lattice of vortex-antivortex pairs within the light-cone which are sensitive to the presence of the quantum phase transition, and can be connected to the dynamical critical exponent. |
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G60.00242: Shaking Wall dynamics in Ultracold atoms Marios Michael, Eugene Demler, Richard Schmidt We analyze dynamics of a one dimensional hydrodynamic fluid in response to periodic shaking of the walls. Experiments of this type can be done with ultracold atoms using either resonantly interacting fermions or bosons. We show that shaking excites phonons through both coherent drive and parametric resonance. We discuss similarities and differences of this type of experiments with the moving mirror problem in a 1d optical cavity. |
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G60.00243: Anomalous excitation enhancement with Rydberg-dressed atoms Jing Qian, Xiaoqian Chai, Lu Zhang, Dandan Ma, Luyao Yan, Huihan Bao We develop the research achievement of recent work [M. G\"{a}rttner, \textit{et.al.}, Phys. Rev. Letts. \textbf{113}, 233002 (2014)], in which an anomalous excitation enhancement is observed in a three-level Rydberg-atom ensemble with many-body coherence. In our novel theoretical analysis, this effect is ascribed to the existence of a quasi-dark state as well as its avoided crossings to nearby Rydberg-dressed states. Moreover, we show that with an appropriate control of the optical detuning to the intermediate state, the enhancement can evoke a direct facilitation to atom-light coupling that even breaks through the conventional $\sqrt{N}$ limit of strong-blockaded ensembles. As a consequence, the intensity of the probe laser for intermediate transition can be reduced considerably, increasing the feasibility of experiments with Rydberg-dressed atoms. |
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G60.00244: Cold-atom Quantum Emulation of Floquet States, Nonlinear Bloch Oscillations, and Quasicrystals Kevin Singh, Kurt Fujiwara, Zachary Geiger, Mikhail Lipatov, Ethan Simmons, David Weld Ultracold lithium atoms in optical lattices provide a versatile platform for investigation of non-equilibrium quantum systems and many-body condensed matter phenomena. We report on experimental characterization of a Floquet phase diagram using bosonic lithium in a strongly-driven optical lattice. Additionally, we present experimental studies of nonlinear real-space Bloch oscillations and progress towards creation of tunable quasicrystalline matter using quasiperiodic optical potentials. |
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G60.00245: Quantum Open System Dynamics in a Nonlinear Environment Chitrak Bhadra, Dhruba Banerjee The Caldeira-Leggett model has been a paradigm for studying open quantum systems for decades via path-integral methods and subsequent works by Zurek has shown its application in understanding the phenomenon of decoherence. Recently, it has been shown that at the classical level, intrinsic nonlinearity of the environment leads to significant changes in correlations and Langevin dynamics of an open system. The quantum counterpart of such a model, employing a canonical formalism, leads to corrections of the standard Quantum Fluctuation Dissipation Relations (FDR) for a Bosonic bath at finite temperatures. The nonlinearity bears the signature of self interaction of the bath modes. On the other hand, a Feynman-Vernon path-integral evaluation of the problem using perturbative expansion reveals a Quantum Master Equation approximated at suitable limits. The effect on decoherence and dissipation can be surmised from this equation and predictions for realistic self-interacting baths can be made. The issue of system-bath coupling strength also shows different characteristics at weak and strong parameter values. |
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G60.00246: First-principles simulation of an optomechanical memory for quantum entanglement Peter Drummond, Run Teh, Simon Kiesewetter, Margaret Reid Optomechanical systems cooled to the quantum level provide a promising mechanism for a high-fidelity quantum memory that is faithful to a given temporal mode structure, and can be recovered synchronously. We carry out full, probabilistic quantum simulations of a quantum optomechanical memory, including nonlinear effects that are usually ignored. This is achieved using both the approximate truncated Wigner and the exact positive P phase space representations. Our simulations allow us to probe the regime where the linearization approximation fails to hold. We show evidence for large spectral overlap between the quantum signal and the transfer field in typical optomechanical quantum memory experiments. Methods for eliminating this overlap to accurately recover the quantum signal are discussed. Using these methods, a strategy for generating EPR entanglement between two separated optomechanical oscillators is analyzed, using entangled radiation produced from downconversion and stored in an initiating cavity. We show that the use of pulsed entanglement with optimally shaped temporal modes can efficiently transfer quantum entanglement into a large-scale macroscopic mechanical mode, then remove it after a fixed waiting time for measurement. |
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G60.00247: Numerical studies of a Matter-Wave Open Quantum System. Ludwig Krinner, Arturo Pazmino, Michael Stewart, Joonhyuk Kwon, Dominik Schneble In a recent experiment [1], we implement a model for an open quantum system consisting of an array of Weisskopf-Wigner type emitters (``artificial atoms'') realized with ultracold atoms in an optical lattice geometry [2]. Each emitter can spontaneously emit matter waves, with fully tunable decay strength and excited state energy. In a recent theoretical analysis [3], we studied a single site coupled to a one-dimensional waveguide and analyzed the transition from Markovian to non-Markovian dynamics including the formation of a bound state. In the experiment, we found strong qualitative deviations of the data compared to the single site analytical treatment. We present numerical studies on the effect of neighboring ground-state emitters, which suggest that the observed differences can be explained in terms of resonant re-absorption of emitted matter waves, such as tunneling and diffusion. We also propose schemes for direct characterization of transport properties in the lattice. |
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G60.00248: Theoretical study on the stability of a vortex ring in an axisymmetrically and harmonically trapped dipolar dondensate I-Kang Liu, Shih-Chuan Gou We theoretically study the stability of a vortex ring (VR) in an axisymmetrically and harmonically trapped dipolar condensate. Specifically, we focus on the case in which the dipoles are all aligned along the axial direction. Assuming a condensate of large size, we approach the problem by taking into account the velocity formula derived from the time-dependent Gross-Pitaevskii equation (GPE) by the method of matched asymptotic expansion in the Thomas-Fermi limit for the filament model of a circular VR subjected to bending-wave instability [1]. The stable region, where VR is robust against the linear instability of bending waves, is determined for wide ranges of scaled dipole strength and aspect ratio of the trapping potential. To visualize the locomotion and probe the dynamical aspect of VR traversing in a realistic dipolar BEC, we numerically solve the time-dependent GPE related to the recently demonstrated dysprosium BEC [2]. Furthermore, we address the effect of quantum fluctuation originating from Lee-Huang-Yang effect [3] in such dipolar BECs. |
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G60.00249: Bose-Einstein condensation in an one-dimensional imperfect crystal José Martinez, Juan Garcia, Miguel Solis
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G60.00250: Analogue black hole in spinorial ultracold condensate Inderpreet Kaur, Sankalpa Ghosh Inderpreet Kaur and Sankalpa Ghosh |
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G60.00251: Emergence of non-abelian magnetic monopoles in a quantum impurity Enderalp Yakaboylu, Andreas Deuchert, Mikhail Lemeshko Recently it was shown that molecules rotating in superfluid helium can be described in terms of |
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G60.00252: Towards assembling defect-free arrays of ultracold strontium atoms for quantum simulation Zeren Lin, Ivaylo Madjarov, Alexandre Cooper, Jacob Covey, Brian Timar, Alexander Baumgartner, Nicholas Redd, Emily Qiu, Dan Ilyin, Manuel Endres We report on progress towards creating two-dimensional arrays of strontium atoms in optical tweezers. Strontium has narrow optical transitions and magic wavelengths, which enable robust cooling, trapping, and coherent manipulation of single atoms. We explore strategies for imaging and cooling atoms in optical tweezers, as well as scaling to larger arrays. We further explore approaches to engineering long-range interactions between strontium atoms via Rydberg states. |
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G60.00253: Lee-Low-Pine Transformation Inspired Hartree-Fock Treatment of the Fermi Polaron Problem Hong Ling, Ben Kain We consider the Fermi polaron problem, where a single impurity interacts with non-interacting host fermions at zero temperature. We apply the Lee-Low-Pine (LLP) transformation to eliminate the impurity degrees of freedom, changing the Hamiltonian into a fermionic LLP Hamiltonian describing a many-body system containing host fermions only. We adapt the self-consistent Hartree-Fock (HF) approach, first proposed by Edwards, to the fermionic LLP Hamiltonian where a pair of host fermions interact with a potential very different from the usual two-body interaction. We apply our HF theory, which has the advantage of not imposing any restrictions on the number of particle-hole pairs, to repulsive Fermi polarons in one dimension. We find that for the case where the impurity has the same mass as the host fermion, the results calculated from our variational ansatz, where the HF orbitals are expanded as the superposition of the free-particle states, are in an excellent agreement with the exact ones of McQuire using Bethe ansatz. This work raises the prospect of using the HF ansatz and its time-dependent counterpart as building blocks for developing all-coupling theory for both equilibrium and nonequilibrium Fermi polarons at higher dimensions. |
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G60.00254: Density Wave Instability in Bilayer Dipolar Systems in the Antoparallel Configuration Bilal Tanatar, E. Akaturk, S. Abedinpour We consider a bilayer of dipolar particles in which the polarization of dipoles is perpendicular to the planes, in the antiparallel configuration. Using accurate static structure factor S(q) data from hypernetted-chain and Fermi hypernetted-chain calculations, respectively |
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G60.00255: Boundary condition effects on the energy spectrum of an one dimensional imperfect crystal Juan Garcia, José Martinez, Miguel Solis We report the energy spectrum and the ground density profile of an interactionless particle gas in an one-dimensional crystal with imperfections. The imperfect crystal is modeled by a Dirac comb potential, where some delta strengths are different from the rest. |
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G60.00256: Laser-Cooled Polyatomic Molecules for Precision Measurement Arian Jadbabaie, Nickolas Pilgram, Nicholas Hutzler Compared to atoms, laser-cooling and trapping of molecules presents a significant challenge due to their complicated energy level structure, arising from additional vibrational and rotational degrees of freedom. However, these same degrees of freedom make molecules an attractive platform for research in a broad collection of fields. For example, the large, easily polarized, internal electromagnetic fields of polar molecules make them a powerful platform for precision measurement searches of physics beyond the standard model (BSM). While BSM searches have been previously performed with cryogenic molecular beam experiments probing physics at TeV energy scales, laser-cooled molecules can provide orders of magnitude improvement in measurement time, probing up to PeV scales. We plan to combine cryogenic buffer gas techniques with laser-cooling of YbOH to preform precision measurements of the Yb nuclear magnetic quadrupole moment (MQM), a signature of BSM physics. Polar, polyatomic molecules, such as YbOH, have energy properties favorable to both laser-cooling and precision measurement. Such work producing ultracold molecules has applications in many fields beyond precision measurement, such as quantum information, many-body quantum dynamics, and ultracold chemistry. |
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G60.00257: Trapping and transforming ions in a surface-electrode chip trap Ping-Xing Chen Trapped ions have long cohere time and are relatively easy to be operated, so they became one of the promising systems for quantum information processing. For scalable quantum information processing, a chip trap is under active consideration. The stable trapping and transformation of the ions in chip traps are necessary for the preparation and operation of the ions states with high fidelity. We designed a surface-electrode chip trap, and show it has excellent ability of trapping ions. Also we proposed a method to carry out equally spaced ions-string in a surface-electrode trap by feedback control. Based on these, we showed the separating and merging ions in the trap by the experiments. |
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G60.00258: Multiplexed Quantum Memory in Cold Rubidium Ensemble Chang Li, Yunfei Pu, Nan Jiang, Wei Chang, Sheng Zhang, Luming Duan Atomic internal states in the ground-state manifold provide an ideal candidate for realization of quantum memory. Quantum interface links stationary qubits in quantum memory with flying photonic qubits in optical transmission channels and constitutes a critical element for future quantum internet. We use crossed acoustic optical deflectors (AODs) to realize a 2D multiplexed random access quantum memory via Duan-Lukin-Cirac-Zoller (DLCZ) scheme and electromagnetically induced transparency (EIT) effect. And further we generate multipartite entanglement between 25 (up to 100) individually addressable quantum interfaces in a multiplexed atomic quantum memory array. |
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G60.00259: Dissipative Quantum Error Correction and Application to Quantum Sensing with Trapped Ions Florentin Reiter, Anders Sørensen, Peter Zoller, Christine Muschik Quantum-enhanced measurements hold the promise to improve high-precision sensing ranging from the definition of time standards to the determination of fundamental constants of nature. However, quantum sensors lose their sensitivity in the presence of noise. To protect them, the use of quantum error-correcting codes has been proposed. Trapped ions are an excellent technological platform for both quantum sensing and quantum error correction. Here we present a quantum error correction scheme that harnesses dissipation to stabilize a trapped-ion qubit. In our approach, always-on couplings to an engineered environment protect the qubit against spin or phase-flips. Our dissipative error correction scheme operates in a continuous manner without the need to perform measurements or feedback operations. We show that the resulting enhanced coherence time translates into a significantly enhanced precision for quantum measurements. Our work [1] constitutes a stepping stone towards the paradigm of self-correcting quantum information processing. |
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G60.00260: High-precision hyperfine interaction characterization by adaptive quantum phase estimation Xin Wang, Panyu Hou, Xiaolong Ouyang, Xianzhi Huang Nuclear spins in solid-state platforms is one of the promising physical systems for quantum computation and quantum simulation due to its extraordinary coherence time and natural existence. To implement the high-fideliy intricate spin control, it is imperative to acquire the complete information of the whole system Hamiltonian. We experimentally characterize the hyperfine interaction between the electron spin of NV center and its weakly coupled nuclear spins provided by the surrounding C-13. We take advantage of dynamical decoupling technique and the adaptive quantum phase estimation method to acquire the precise hyperfine parameter efficiently. We achieve high-fideliy (>90%) initialization for 6 nuclear spins. A hybrid system consisted of six nuclear spins and one electron spin, provides the possibility to complete the complicated task of quantum computation and quantum simulation. |
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G60.00261: Optical Analogue of Irreversible Quantum Theories Giulia Marcucci, Claudio Conti Foundations of quantum mechanics are designed by their physical interpretation: each observable must be a Hermitian operator to guarantee the reality of its spectrum, and wave functions must belong to a Hilbert space with a conserved probability measure. Recently, extended quantum theories have been developed by replacing the Hermiticity condition with the weaker requirement of a complex space-time-symmetric (PT-S) Hamiltonian with real-valued eigenvalues. In addition, various authors developed time asymmetric (TA) QM with complex energy eigenvalues, which account for irreversible evolution. |
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G60.00262: Chaos and Bifurcations in the Monopole Ion Trap Edgar Perez, John Essick The monopole ion trap is based on the dynamic stabilization of a charged particle near an electric field maximum. The trap uses strong defocusing to confine the particle to a region between two concentric spherical electrodes, and this spherical geometry leads to a nonlinear equation of motion. The system has been previously studied as a periodically driven nonlinear oscillator, and numerical results suggest that a trapped particle follows a period-doubling route to chaos. In this experiment, charged polyethylene microspheres were trapped using the simultaneous application of static and alternating voltages. The microspheres were charged using the triboelectric effect and their motion was captured using a high-speed digital camera. We report the experimental observation of three bifurcations towards chaos and a period-three attractor. |
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G60.00263: Performing Electron Interferometry Using a Transmission Electron Microscope with an Thermionic Source Rose Marie Haynes, Gino Carrillo, Fehmi Yasin, Benjamin McMorran Here we demonstrate the capability of the FEI Tecnai Spirit Transmission Electron Microscope (TEM) to perform electron interferometry. This TEM, like many other older models, uses a thermionic emission source with low spatial coherence. Presently, electron interferometry can be performed in a TEM using methods such as the Mollenstedt Biprism, but such methods require much higher spatial coherence than can be attained with lower-end TEMs. By using a nanofabricated grating as a beam splitter, we are able to perform electron interferometry with much lower spatial coherence. The goal of this experiment was to verify that older TEMs could be used to study the properties of electron-transparent materials using this method. Gratings were milled with a pitch of 200 nm and a diameter of 20 μm using a focused ion beam. The grating was placed in the aperture of the TEM and was used to split the electron beam into spatially separated, well-focused diffraction orders at the specimen plane. By refocusing these diffraction orders we obtained an image of the grating in which the sinusoidal features on the grating were visible, suggesting that electron interferometry can be performed in TEMs with thermionic emission sources. |
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G60.00264: Dynamics of a small dielectric sphere due to the higher-order modes of an optical nano fiber Emma Brinton, Michael Wolff, Benjamin Jenkins, C. Leary We investigate the dynamics of a submicron-scale, dielectric sphere in the electromagnetic field from an optical nanofiber. Modeling the sphere as a damped, oscillating dipole driven by the nanofiber field, we calculate the time-averaged force on the sphere. For a given monochromatic field, we quantify the dependence of this force on the radii of the sphere and the nanofiber, as well as the the refractive indices of the sphere, nanofiber, and surrounding region. We analyze the resulting motion of the sphere in the presence of several higher-order nanofiber modes. |
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G60.00265: Liquid height measurement based on laser ranging method Bicheng Chen Liquid height measurement plays an important role in many industrial applications. However, most current methods obtain interval time-depending datas. The laser ranging method obtains the integral fluid height, which is very sensitive to the change of laser intensity. The measuring structure is a vertically fixed multimode optical fiber as illuminating and receving device. Place the foamed plastic platform on the liquid and paste a mirror as a reflector on the platform. The light emitted by the optical fiber is reflected and received, which has a gaussian curve relation to the distance between the fiber and the liquid. |
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G60.00266: Non-Gaussian optical vortex in a degenerate resonator with an intra-cavity spiral phase plate YuanYao Lin We propose a simple concept to generate non-Gaussian optical vortex beams using a near semi-spherical optical cavity with an intra-cavity spiral phase plate (SPP). Although the azimuthal symmetry breaking induced by SPP prevent Laguerre Gaussian mode to oscillate in the resonator, the beamlet retracing skewed V-shaped paths by the aid of beamlet coupling effect in the resonator are coherently phase-locked to form coherent optical vortex beam with wavefront dislocation mirroring the topological charge of the SPP. The circulating skewed V-shaped beamlet paths can be modeled by coupled mode equations taking into account linear coupling, laser gain and resonator loss. Experimental demonstrations using diode-pumped Nd:YAG solid state system emitted randomly polarized non-gaussian optical vortices of a positive unit topological charge at a central wavelength of 1064 nm when the pump power went above 1.52 W. Moreover This system also serves an useful platform to shape laser beams structurally, to study the laser dynamics and to combine radiations coherently. |
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G60.00267: Comparative study of the optical nonlinearity of atomic and molecular gases driven by an intense 10 µm CO2 laser Jeremy Pigeon, Sergei Tochitsky, Eric Welch, Chan Joshi Measurements of the optical nonlinearity of atomic and molecular gases are important for understanding light-matter interactions at high intensities. While the wavelength scaling of the nonlinear refractive index of these gases at visible and near-IR wavelengths has been studied extensively, there is a lack of measurements for the long-wave infrared(LWIR) wavelengths that are far from electronic resonance. In this range, rovibrational Raman transitions may introduce a resonant contribution to the optical nonlinearity of molecules. Further, LWIR radiation at intensities up to 1012 W/cm2 may modify the electronic nonlinearity of these gases while still remaining below the tunnel or multi-photon ionization threshold. We have experimentally studied the four-wave mixing of picosecond, 10 µm, CO2 laser pulses at an intensity up to 1010 W/cm2 in a gas-filled cell. Here we report the first measurements of the effective nonlinear refractive index of the diatomic molecules N2 and O2 and the noble gases Kr and Xe at 10 µm. We have observed that the molecular nonlinearity dominates the effective nonlinear refractive index. |
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G60.00268: Resolution of a discrepancy in elastic electron scattering from water Leigh Hargreaves, Luis Rios, Thalia Linsky The 2008/2012 measurements of Khakoo et al., and the 2004 measurements of Cho et al. of elastic electron scattering from water, both employing the well known relative flow method (RFM), showed variation beyond the limits of their error bars. Khakoo et al. employed an aperture gas collimator instead of the standard capillary, an approach designed to remove any physical assumption about water's gas diameter from the RFM. They hypothesized that the differences were the result of Cho et al. employing an unsuitable estimate of the gas diameter. However, the data of Cho et al. agrees better with modern quantum chemical calculations, which is curious if their approach was systematically flawed. This discrepancy is important as water plays a vital role in the chemistry of biological environments. |
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G60.00269: Photochemical Transformation on Plasmonic Nanoparticles Via Resonant Radiated-Induced Heating Simol Shah Stable coupled interaction between the interfaces of plasmonic nanomaterials and electromagnetic fields have governed photophysical processes amplified by light-matter interaction. Said interaction recently entertained a breadth of study in photochemical catalysis as optically excited plasmons of the nanoparticle metallics are keen to chemical transformations on their sufaces. To illustrate underlying physical mechanisms responsible for observed chemical activity, plasmon-mediated photocatalysis is delivered through oscillations of quantum energy emitters, resulting in non-radiative process of plasmon decay, fertile to chemical transformation. Thermalization, the parameter by which quantum emitters are chemically adjusted, bodes well for surveyance of the energy transfer and dissipation into the environment by nanoparticle phonon modes. In presence of heat, electron-driven reduction chemistry is spatially mapped akin to electromagnetic near fields, with nanometric resolution as function of time and electromagnetic field polarization with regard to variant plasmonic nanostructures. The resultant localization of reactive regions, determined by thermally-induced-carrier transport from high-field regions, prefaces way for efficiency in its nanoscale regio-selective surface chemistry. |
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G60.00270: Hyperfine Resolved Spectrum of the a4Σ–3/2–X2Π3/2 System of Gaseous Gold Sulfide (AuS) in the Near Infrared Thomas Varberg, Gleason Samuel, Austin Parsons We have recorded the electronic spectrum of the a4Σ–3/2–X2Π3/2 system of gold monosulfide (AuS) in the near infrared region. The molecules were produced by sputtering gold in a hollow cathode discharge source followed by reaction with carbonyl sulfide (OCS). We recorded initial scans at low resolution using a pulsed laser that revealed a vibrational progression from the (0,0) to (5,0) bands, covering the region from 821 to 721 nm. Many hot bands were also observed. Following this work, the (2,0), (1,0) and (0,0) bands were recorded, first at Doppler-limited and then at sub-Doppler resolution using a continuous-wave Titanium:Sapphire ring laser. The ground state of AuS is an inverted 2Π state with a spin-orbit splitting of 1318.5 cm–1. From our least-squares fitting, we have determined accurate values for the vibrational, rotational and hyperfine parameters of the a4Σ–3/2 and X12Π3/2 states. |
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G60.00271: Density dependence of the effective mass in a GaAs quantum well X Fu, Q Ebner, Qianhui Shi, Michael Zudov, Qi Qian, John Watson, Michael Manfra We performed effective mass measurements employing microwave-induced resistance oscillation in a tunable-density GaAs/AlGaAs quantum well. Our main result is a clear observation of an effective mass increase with decreasing density, in general agreement with earlier studies which investigated the density dependence of the effective mass employing Shubnikov–de Haas oscillations. This finding provides further evidence that microwave-induced resistance oscillations are sensitive to electron-electron interactions and offer a convenient and accurate way to obtain the effective mass. |
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G60.00272: Effect of density on the amplitude of microwave-induced resistance oscillations Michael Zudov, X Fu, Mikhail Borisov, John Watson, Michael Manfra We have measured microwave-induced resistance oscillations (MIRO) in a tunable-density 30 nm-wide GaAs/AlGaAs quantum well and observed that the MIRO amplitude increases dramatically with carrier density. The analysis shows that the increase in the effective microwave power and quantum lifetime with density are not sufficient to explain the observed growth of the oscillation amplitude. We further found that the fundamental MIRO extrema move towards cyclotron resonance with increasing density, in contrast to theoretical predictions. These unexpected findings reveal that the density dependence is not captured by existing theory. |
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G60.00273: Conformational response of a membrane protein (CorA) by a coarse-grained model Warin Jetsadawisut, Sunan Kitjaruwankul, Panisak Boonamnaj, Sunita Paudel, Pornthep Sompornpisut, Ras Pandey Conformational response of a membrane protein (CorA) plays an important role in modulating the pathways for selective transport of Mg2+ through its ion channel. Using a coarse-grained Monte Carlo simulation, we investigate the conformation of inner (iCorA) and outer (oCorA) segments of the protein CorA in its native and denature phases. In denature phase, the radius of gyration of both segments is found to increase with the temperature, a continuous response of iCorA and an abrupt response of oCorA [1] in a narrow range of temperature. The radius of gyration of iCorA contracts on raising the temperature in native phase in contrast while oCorA appears less organized. The conformations of these segments are quantified by estimating its effective dimension from a scaling analysis of the structure factor. |
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G60.00274: QUANTUM INFORMATION, CONCEPTS AND COMPUTATION
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G60.00275: Human Quantum Energy Levels Maria Kuman Bragg scattering, which is elastic neutron scattering, revealed that helium nanodroplets at very low temperatures have torus shaped NEMF [2]. When the donuts were belched at the equator (which meant the donuts were spinning faster), turbulence was observed as a chain of alternating vortices and anti-vortices in the equatorial area [2]. The observed peaks of neutron scattering indicate specific energy transfers hνij between discrete states, which means discrete quantum energy levels were present when turbulence was present. It seems that quantum energy levels are specific for all spinning systems exhibiting turbulence: starting with the elementary particles, which emit and suck back virtual photons from their equatorial area, and finishing with the sun, which emits spinning plasma balls from anti-vortices in its equatorial area, which after a curved trajectory are sucked back by nearby vortices. Measurements and Kirlian photographs [2], [4] of the light of the human NEMF show that our NEMF is also donut-shaped and did have discrete energy levels, just like the atoms of which our material body consists. |
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G60.00276: vcbcvb Dusica Zegarac Dougherty Ħ ħ Ħ ħ |
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G60.00277: Characterizing microwave loss mechanisms induced by magnetic fields in microstrip superconducting resonators. Sangil Kwon, Anita Roudsari, Olaf Benningshof, Yong-Chao Tang, Hamid Mohebbi, Ivar Taminiau, Deler Langenberg, Shinyoung Lee, George Nichols, David Cory, Guoxing Miao We describe an experimental approach to investigating the magnetic field dependent microwave losses in superconducting niobium microstrip resonators. The key parameters characterizing the losses are obtained by studying the dependence of the resonant frequency and the quality factor on magnetic fields along various directions, and comparing the experimental data with numerically calculated values. We propose a general way to identify contributions from quasiparticle generation and vortex motion to microwave losses. |
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G60.00278: Hydrogen as a Source of Flux Noise in SQUIDs Ruqian Wu, Zhe Wang, Hui Wang, Clare Yu
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G60.00279: Genuine N-partite entanglement without N-partite correlations Cong Minh Tran, Margherita Zuppardo, Lukas Knips, Anna de Rosier, Wieslaw Laskowski, Harald Weinfurter, Tomasz Paterek A genuinely N-partite entangled state may display vanishing N-partite correlations measured for local observables. In such states the genuine entanglement is noticeable solely in correlations between subsets of particles. A straightforward way to obtain such states for odd N is to design an “antistate” in which all correlations between an odd number of observers are exactly opposite. Evenly mixing a state with its antistate then produces a mixed state with no N-partite correlations, with many of them genuinely multiparty entangled. Intriguingly, all known examples of “entanglement without correlations” involve an odd number of particles. We conjecture that there is no antistate to any pure even-N-party entangled state making the simple construction scheme unfeasible. However, higher-rank examples of entanglement without correlations for arbitrary even N indeed exist. These classes of states exhibit genuine entanglement and even violate a Bell inequality, demonstrating the nonclassical features of these states as well as showing their applicability for quantum information processing. |
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G60.00280: Mesoscopic steerable superposition states and Einstein-Podolsky-Rosen steering in a Bose-Einstein condensate Margaret Reid, Bogdan Opanchuk, Bryan Dalton, Peter Drummond, Andrei Sidorov, Laura Rosales-Zarate In 1935, Einstein, Podolsky and Rosen (EPR) presented their “paradox” that established inconsistency between the completeness of quantum mechanics and local realism. States that show an EPR paradox are called EPR-steerable. We present experimental evidence for genuinely steerable states involving thousands of atoms. Using theory based on superselection rules, we analyze experiments where atoms are cooled to form a Bose-Einstein condensate (BEC). We show that large groups of atoms become indistinguishable particles occupying two distinguishable modes that are EPR-steerable. |
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G60.00281: Quantum Zeno - Inverse Quantum Zeno Considerations in Unstable Systems Onofrio Russo, Oktay H Gokce
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G60.00282: The Essence of Delayed Choice Entanglement Elimination Douglas Snyder One can tie a delayed choice on one of two entangled particles (particle 1) before particle detections to the presence of entanglement or absence of entanglement to differentially affect the other particle (particle 2). This effect on particle 2 can result in the development of distinct types of distributions of particle 2 that exhibit either the absence or presence of interference. The foregoing is the essence of delayed choice entanglement elimination. The particular distribution obtained for particle 2 depends on making the same choice on particle 1 over a number of runs. If over a number of runs the choice on particle 1 is to preserve entanglement, then the relevant distribution of particle 2 will not show interference (instead the one broad hump demonstrating which-way information). If over a number of runs the choice on particle 1 is to eliminate entanglement, then the relevant distribution of particle 2 will show interference. No correlations are needed between the measurements on the paired particles to develop either of the two possible distributions of particle 2. Delayed choice entanglement elimination can be used to develop a non-trivial non-local quantum communication system. |
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G60.00283: Quantum Thermodynamics of Parametrically Driven Linear Systems Leonardo Pachon, Andres Estrada Thermodynamics theory resides the assumption that interacting systems can be clearly defined and distinguished from each other. The physical justification of weak coupling limit in the theory of open quantum systems and quantum thermal machines relies on the assumption that the region in contact is so small compare to the whole volume, that its mixing or any boundary or interface effect may be completely neglected. To explore the situation when the system and the bath interaction is not weak, the power extraction in a parametrically driven linear systems is analytically derived in the strong coupling regime. Heat rectification in this regime is possible as long as the thermal inertial is overcome by the parametric driving. |
(Author Not Attending)
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G60.00284: Temperature controlled preferential orientation of Nitrogen-Vacancy centers in CVD grown (113) diamond crystal Mohammad Akhtar, S. Chouaieb, L.J. Martinez, I. Gross, A. Tallaire, J. Achard, I. Philip, A. Dreau, Vincent Jacques The electronic spin system of nitrogen-vacancy (NV) center in diamond has emerged as an excellent nanoscale sensor for detection and imaging of weak magnetic fields. Specifically, using an ensemble of n defects allows to enhance the detection sensitivity by a factor √n, provided that all centers are oriented along the same direction. Here we show that for CVD grown (113) diamond crystal, the growth temperature can be used as a controlled parameter for creating NV centers aligned along one of the four possible orientations in the crystal. We further show that this technique can be combined with delta-doping to generate thin concentrated layers of preferentially oriented NV centers. Besides increasing performances in quantum sensing, the control of deep point defect orientations in solids will also benefit in quantum information and quantum communication applications. |
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G60.00285: VSi based vector-magnetometry in 4H-Silicon Carbide - status quo and future Matthias Niethammer, Matthias Widmann, Sang-Yun Lee, Pontus Stenberg, Olle Kordina, Takeshi Ohshima, Nguyen Son, Erik Janzen, J. Wrachtrup Silicon Carbide (SiC) as an emerging quantum host material provides many defects for quantum applications. The electronic properties and mature industrial background make it especially attractive for integration of quantum sensing systems. We demonstrate the theory of sensing of all 3D-Vector components of external magnetic fields using spin 3/2 systems and show practical data using silicon vacancies in 4H-SiC. The dim fluoresence of silicon vacancies and lower spin contrast compared to diamond based approaches decrease sensitivity using similar to already known techniques. We here also present ideas and approaches currently under investigation on how to overcome these problems in silicon carbide by exploiting its electrical and manufacturing advantages and combining different fields of modern material science with spin defects in solid state materials. |
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G60.00286: Quantum Search Without Entanglement: Database Search with Magnonic Holographic Devices Alexander Khitun, Michael Balinskiy, Howard Chiang, David Gutierrez We present experimental data demonstrating the implementation of quantum algorithms (e.g., Deutsch–Jozsa algorithm) using classical Magnonic Holographic Device. MHD is a type of holographic device which utilizes spin waves for data transfer and processing. Its operation is based on the correlation between the phases of the input spin waves and the output inductive voltage. The latter makes it possible to code logic states into the phases of propagating waves and exploit wave superposition for parallel data processing. We present experimental data on database search through a five-dimensional phase space. It takes 65 queries to find the combinations resulting in the maximum output. The solution of the same problem would take 1024 queries for the classical computer. We argue that the use of classical wave superposition may provide the same speedup in database search as for true quantum computers. |
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G60.00287: Factorization of Linear Quantum Systems with Delayed Feedback Gil Tabak, Ryan Hamerly We consider the transfer functions describing the input-output relation for a class of linear open quantum systems involving feedback with nonzero time delays. We show how such transfer functions can be factorized into a product of terms which are transfer functions of canonical physically realizable components. We prove under certain conditions that this product converges, and can be approximated on compact sets. Thus our factorization can be interpreted as a (possibly infinite) cascade. Our result extends past work where linear open quantum systems with a state-space realization have been shown to have a pure cascade realization [Nurdin, H. I., Grivopoulos, S., & Petersen, I. R. (2016). The transfer function of generic linear quantum stochastic systems has a pure cascade realization. Automatica, 69, 324-333.]. The functions we consider are inherently non-Markovian, which is why in our case the resulting product may have infinitely many terms. |
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G60.00288: Closed-Loop Optimized Control Strategies for Adiabatic Quantum Computation in the Presence of Noise Gregory Quiroz We extend recent work focused on closed-loop optimization for adiabatic quantum computation (AQC) control schedules and assess the robustness of a number of closed-loop noise mitigation strategies in the open system setting. First, we investigate the robustness of the previously developed approach in the open system setting and characterize optimal performance regimes with respect to noise parameters. Second, we modify the approach to optimize amplitudes of terms in the AQC Hamiltonian, such as the local bias and tunneling strengths of the initial Hamiltonian. We find that the latter approach can be considerably more robust than schedule optimization for random Ising problem Hamiltonians. Lastly, the technique is extended to stabilizer subsystem code encoded AQC evolution to optimize the static and time-dependent amplitudes of energy penalties, where considerable improvements over uniform static energy penalties is observed for random Ising chain problems. |
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G60.00289: Interpertation and Origin of the sideband asymmetry of a mechanical oscillator close to the ground state Liu Qiu, Itay Shomroni, Nicolas Piro, Daniel Malz, Andreas Nunnenkamp, Tobias Kippenberg Cavity Optomechanics provides an unique way to probe the quantum mechanical motion of a macroscopic oscillator. Motional sideband thermometry has been shown in different measurement schemes to calibrate the phonon bath. In this experiment, we performed the motional sideband asymmetry measurement with multiple tones scheme in the optical domain for the first time. Using a heterdyne detection scheme, the output noise spectrum reveals the correlation between the imprecision and quantum backaction. Besides, we observed an effective Kerr-type optical nonlinearity due to the optical absorption heating. The finite cavity thermal response would produce artifical sideband asymmetry when the cooling tone and the red tone are close. This spurious sideband asymmetry is analyzed with a detailed theoretical model. Our measurement provided a lot of insight towards multiple tones optical measurement in cavity optomechanics, such as back-action evasion measurement and quantum mechanical squeezing. |
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G60.00290: Shannon information theory in heat engines Mohammad Ansari Open quantum system techniques help us to understand how density matrix evolve in subsystems. This is only useful to evaluate time evolution of physical quantitues, which are linear in density matrix. Shannon entropy is not so, in fact it is nonlinear in density matrix. We introduce a technique, called extended Keldysh formalism, to understand time evolution of nonlinear quantities in density matrix. As result we show that Shannon entropy can evolve using much larger class of Kubo-Martin-Schwinger correlators, therefore evaluation of Shannon entropy based on standard open quantum techniques, such as Lindblade equations etc., are misleading and inconsistent with quantum nature of entropy. We address inconsistencies and also address new results. |
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G60.00291: Efficient numerical optimization using quantum trajectories Michael Goerz, Kurt Jacobs The wave-function Monte-Carlo method, also referred to as the use of "quantum trajectories", allows for the efficient simulation of open systems by independently tracking the evolution of many pure-state "trajectories". Numerical optimal control theory is a versatile tool for the design of control fields that steer a quantum system towards some goal, e.g. the creation of a highly entangled state. Here we show that Krotov's method of optimal control can be modified in a simple way to be fully parallel in the pure states. This provides a highly efficient method for finding optimal control protocols for open quantum systems and networks with typically large Hilbert spaces. We apply this method to the problem of generating entangled states in a network. We show that due to the existence of a dark-state subspace, nearly-optimal control protocols can be found by using only a single pure-state in the optimization, further increasing the efficiency. |
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G60.00292: Quantum Correlations Established During Non-Markovian Optimal Sideband Cooling Andres Estrada, Johan Triana, Leonardo Pachon Optimal control theory is applied to sideband cooling of nano-mechanical resonators. The formulation described here makes use of exact results derived by means of the path-integral approach of quantum dynamics, so that no approximation is invoked. It is demonstrated that the intricate interplay between time-dependent fields and structured thermal bath may lead to improve results of the sideband cooling by an order of magnitude. Cooling is quantified by means of the mean number of phonons of the mechanical modes as well as by the von Neumann entropy. Quantum correlations established during the optimal sideband cooling are discused. |
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G60.00293: Effects of counter-rotating-wave terms on the non-Markovianity in quantum open systems Wei Wu We investigate the effect of counter-rotating-wave terms on the non-Markovianity in quantum open |
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G60.00294: In Situ Characterization of Qubit Control Lines: A Qubit as a Vector Network Analyzer Markus Jerger, Zénon Vasselin, Arkady Fedorov In quantum control and quantum computing applications, it is crucial that the control signals reaching the device are free from distortion. |
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G60.00295: Parity-preserving light-matter system mediates effective two-body interactions Thi Ha Kyaw, Sebastian Allende, Leong-Chuan Kwek, Guillermo Romero We study the equilibrium and non-equilibrium physics of two qubits interacting through an ultrastrong coupled qubit-cavity system. By tuning the qubits energy gap while keeping the ultrastrong coupling system to its ground state, we demonstrate a strong two-qubit interaction as well as an enhanced excitation transfer between the two qubits. Our proposal has twofold implications: a means to attain multipurpose parity-protected quantum information tasks in superconducting circuits and a building block for ultrastrong coupled cavity-enhanced exciton transport in disordered media. |
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G60.00296: Detailed Study of microwave-activated c-Phase (MAP) gate in tunable 3D transmon two qubit system Taewan Noh, GwanYeol Park, Gahyun Choi, Jiman Choi, Woon Song, Soon-Gul Lee, Kibog Park, Yonuk Chong Two-qubit microwave-activated c-Phase (MAP) gate was experimentally demonstrated earlier by Chow et al. [1]. Although MAP gate is an easily realizable entangling scheme between two fixed-frequency transmon qubits, it has not been extensively studied afterwards. In this study, we have investigated the performance of MAP gate in detail as an entangling gate, for the purpose of implementing it into simple quantum algorithms. Instead of using two fixed-transition frequency qubits, we used a tunable-frequency qubit in order to align the higher energy levels in situ to optimize the interaction between those levels. As a characterization of MAP gate, we will present the result of tomographic reconstruction of density matrices of various entangled states realized by MAP gate. |
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G60.00297: fabrecation and measurement of transmon qubit Ma Yulin Superconducting qubit is considered to be an important component of quantum computer, and transman, as a kind of superconducting qubit, has been widely studied in recent ten years. we hope that through the research to fabrecate transmon qubit that have long coherent time, high fidelity and stability. we use aluminum to prepare transmon qubit and microwave resonators, use micro nano machining technology (such as electron beam lithography, photo lithography, evapreation, inductively coupled plasma etc.) to fabrecate qubit device. we use dilution refrigerator to make sure the device is measure in the tempreture of milli kelvin. we use microwave circuit to measure the transmon qubit. now life time of our transmon qubit is stablely more than 10 microsecond. |
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G60.00298: A tunable J-gate for spin qubits in donors coupled to an interface Peihao Huang, Garnett Bryant A tunable J-gate for spin qubits in donors coupled to an interface |
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G60.00299: Simple and Scalable Method for Generation of Trapped Ions’ W State Chun-Wang Wu, Ping-Xing Chen By introducing auxiliary energy levels, we propose a simple and scalable method for generation of trapped ions’ W state. In our proposal, except the addressing phase shift operation for the first ion, all the other unitary operations (include typical carrier and sideband transitions) can be implemented using global laser beam, so the experimental difficulty can be largely reduced. Furthermore, the number of the laser pulses for W state generation is independent of the size of the W state, so our proposal is highly scalable. This method may be applied to generation of large-size entanglement of trapped ions in the near future. |
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G60.00300: ENERGY RESEARCH AND APPLICATIONS
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G60.00301: Gyrokinetic Simulation of Ion-Temperature-Gradient Mode in the presence of Radio-Frequency Waves S Sen, K Imadera, Y Kishimoto In our earlier work (REDS Plasma Science and Technology,171, 52 (2016)) the ion temperature |
(Author Not Attending)
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G60.00302: Tensile-strain-dependent thermal conductivity study of a single-crystal thin film in the vacuum environment Mingi Kang, Qing Hao, Dongchao Xu, Fabian Medina, Xuewang Wu, Jie Zhu, Xiaojia Wang Stretchable electronics have recently received increased attention for their wide applications for tactile sensor for artificial skin electronics, wearable devices, and stretchable displays. Along this line, the strain-dependent thermal conductivity of stretched material can be of significance to many energy-related applications. In the literature, the very few thermal measurements for films under uniaxial tensile strains have all been conducted in ambient condition and the accuracy of measurements is affected by convection.[1-2] In this work, a single-crystal thin film has been measured for its tensile-strain-dependent thermal conductivity along both the in-plain and cross-plain directions. The state-of-the art pump-probe technic is used for high-vacuum and temperature-dependent measurements. The results presented here can be important to many strain-engineering applications. |
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G60.00303: Thermionic emission and surface cooling from functionalized carbon nanotube oxide thin films Feng Jin Thermionic emission is widely used in applications where strong electron emission is essential. Thin film type of thermionic emitters, however, despite of its versatility and potential, has yet to appear in real device applications. The main shortcoming for thin film thermionic emitter is its weak emission capability as compared to its bulky conventional counterparts. A high performance thermionic emission thin film with emission capability in par with that from a regular thermionic source is presented here. This thin film is based on carbon nanotubes (CNTs) with its surface further functionalized with low work function oxide materials. The low-work-function oxide coating combines with a large Schottky effect induced by the CNTs, results in a dramatic increase of thermionic emission. Emission current density as high as 4.5 A/cm2 is obtained, and such emission capability exceeds most of the conventional thermionic cathodes used today. |
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G60.00304: NMR and Magnetic Study of Half-Heusler Semiconductor NbFeSb Yefan Tian, Hangtian Zhu, Wuyang Ren, Zhifeng Ren, Joseph Ross The Half-Heusler semiconductor NbFeSb has been of considerable interest due to its excellent thermoelectric performance, especially its enhanced power factor.[1] To further investigate the electronic properties of these materials, we have done 93Nb NMR and magnetic measurements on several NbFeSb samples with different defect densities, prepared at a series of hot pressing temperatures. Magnetization measurements show the presence of paramagnetic defects in undoped samples with a concentration of about 0.002 per formula unit independent of processing. MAS NMR measurements yield narrow lines with almost identical shifts of +3600 ppm. Changes in static-NMR line widths and amplitudes indicate a significantly larger concentration of apparently electrically inactive defects for samples prepared at lower processing temperatures. In addition, the NMR T1 relaxation time measurements vs. temperature indicate a wide distribution of local behavior which we have analyzed in terms of the distribution of magnetic defects in these samples. [1] He et al., Proc. Natl. Acad. Sci. U. S. A. 113, 13576-13581 (2016). |
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G60.00305: Hopping-type Modifications of Quantum Interference Conditions in Nanoscale Thermal Junctions Hunter Tonn, Kamil Walczak We examine quantum processes of heat (energy) transfer as carried by electrons transfered between two metallic heat reservoirs (thermal baths) via the system of coupled quantum dots in several interesting configurations, where quantum interference effects become essentially important. Our investigations are based on the hypothesis that quantum interference effects may be used to control nanoscale heat conduction. Our computational method is based on Landauer formula for heat flux expanded into Taylor series with respect to temperature difference in order to obtain expressions for thermal conductance and its nonlinear correction in terms of transmission probability function. The connections with heat reservoirs are treated within the Newns-Anderson model with semi-elliptical density of electronic states. Our results are discussed with respect to average temperature, resonant states, and specific hopping-like parameters characterizing connections between quantum dots and thermal baths. |
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G60.00306: Thermal and Shot Noises Generated by Hot Electrons in Quantum-Interference Devices Omar Tsoutiev, Kamil Walczak Quantum interference effects may be used to control nanoscale transport phenomena, including heat conduction and heat conversion processes. We present computational method that can be used to calculate thermal and shot noises associated with high-intensity heat fluxes carried by hot (energetic) electrons within the Landauer scattering formalism. The transmission probability functions for different configurations of the system of coupled quantum dots connected to metallic heat reservoirs (thermal baths) are calculated by using the theory of propagators. The connections with heat reservoirs are treated within the Newns-Anderson model with semi-elliptical density of electronic states. We used perturbative technique to determine noise power spectra with up to the second order terms in relation to temperature difference. Our results are discussed with respect to average temperature and the strength of specific connections between quantum dots and thermal baths. |
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G60.00307: Energy Band Alignment of ZnSxSe1-x Films on Si for Photovoltaic Carrier-Selective Contacts Rebecca Glaudell, Harry Atwater ZnSxSe1-x films are promising materials for front carrier-selective contacts in silicon photovoltaics given their wide bandgaps and low resistivities compared to amorphous silicon. X-ray photoelectron spectra of ZnSxSe1-x films (x ranging from 0 to 1) grown on Si by molecular beam epitaxy were used to measure the conduction band and valence band offsets of ZnSxSe1-x with respect to Si for purposes of accurate optoelectronic simulations of photovoltaic devices incorporating ZnSxSe1-x carrier-selective contacts. Conduction band offsets ranged from 0.42 eV (x = 1) to 1.52 eV (x = 0) showing a significant departure from both Anderson model and density functional theory predictions. These offsets represent transmission probabilities through the ZnSxSe1-x depletion region of 94%–0% for an electron in the bulk silicon conduction band, suggesting Se-rich ZnSxSe1-x films will be necessary for effective ZnSxSe1-x electron-selective contacts on Si. The open-circuit voltage, fill factor, and conversion efficiency of ZnSxSe1-x/Si cells will be discussed. |
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G60.00308: Polymer Back Contacts and the Efficiency of Cadmium Telluride (CdTe) Solar Cells Tyler Lucas, Brooke Myers, Prof Weining Wang First Solar has announced that the highest efficiency of CdTe/CdS solar cells is still lower than the theoretical limit. This comes from how hard it is to form a good ohmic back contact on p-type CdTe. CdTe has a high electron affinity (~4.5 eV), so a metal with a high work function is necessary to form a good ohmic contact with CdTe. Conductive polymers are candidates for the back contact because they have high work functions, high conductivities, are easy to process, and cost less. Our previous studies show that poly(3,4-ethylenedioxythiophene) polystyrene sulfonate can be used as the back contact of CdTe solar cells with promising results. |
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G60.00309: Temperature Dependent Photocurrent Mapping in Halide Perovskite Photovoltaics Luke McClintock, Rui Xiao, Yasen Hou, Dong Yu The current global photovoltaic market is almost exclusively composed of silicon-based solar cells. Nonetheless, the power conversion efficiency (PCE) of these cells has only increased by 1.6% over the past 17 years. Hybrid organic-inorganic metal halide perovskite compounds, such as methylammonium lead iodide (MAPbI3), however, have leapt from PCEs of 3% to over 20% in just the last five years. Due to this rapid progress, emerging solar cells based on these materials have already begun to rival silicon photovoltaic efficiencies. In fact, many experts anticipate that perovskite solar cells will be one of the cheapest and most versatile photovoltaic technologies of the future. Fundamental understanding of the underlying perovskite material physics is critical to developing improved perovskites with reduced toxicity, increased stability, and removal of hysteresis in their electronic devices. We have performed temperature and external electric field dependent scanning photocurrent microscopy on single- and poly-crystalline MAPbI3 samples in order to discern the dominating charge transport mechanism, among ferroelectricity, ion migration, charge traps, and field-screening, which governs the unique characteristics of the halide perovskite materials. |
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G60.00310: Structural, Optical, and Ferroelectric Properties of CH3NH3PbI3-xClx: BTO Nanocomposite Thin Films Deposited via Aerosol Assisted Chemical Vapor Deposition for Perovskite Solar Cells Daniel Morales Perovskite solar cell technology is the fastest-advancing solar technology to date. The power conversion efficiency of perovskite solar cells increased from 3.13 % in 2009 to 22.1 % within 6 years. Organolead halide perovskites, specifically methylammonium lead iodide chloride, (CH3NH3PbI3-xClx) is a promising candidate to harvest solar energy. Ferroelectrics can be exploited to reduce bimolecular recombination because spontaneous electric polarization associated local internal electric fields can be used to reduce charge carrier recombination hence photo current density can be enhanced. In this work, we explore structural, optical, and ferroelectric properties of CH3NH3PbI3-xClx: BTO (a well-known ferroelectric material) nanocomposite thin films fabricated via the process of Aerosol Assisted Chemical Vapor Deposition (AACVD). Structural and optical measurements demonstrate as BTO concentration increases in the composite thin films, the crystallinity and optical absorption of composite thin films decrease. The perovskite grain size in the composite decreases as well. Structural, optical, and ferroelectric characterization of CH3NH3PbI3-xClx: BTO nanocomposite thin films fabricated at different BTO nanoparticle concentrations will be presented. |
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G60.00311: Bandgap engineering of oxinitride nanowires for water splitting and hydrogen generation Nikhil Reddy Mucha, Manosi Roy, Chandra Shekar Reddy Nannuri, Dhananjay Kumar, Hemali Rathnayake z-scheme solar water splitting using semiconductor electrodes and photocatalysts is exciting approach for hydrogen generation.As many oxide photocatalysts only respond to UV radiation for watersplitting and under visible light the number of photocatalysts are limited.It is important to develop visible light driven photocatalyst materials for solar water splitting via suitable bandgap engineering.The bandgap of visible light driven photocatalyst should be less than 3.00 eV(λ>415nm).TiN nanowires are converted very controllably to TiN1-xOx by bringing a trace amount of oxygen during the growth.TNO is semiconducting whose bandgap is a function of oxygen.By controlling oxygen content in TNO,we are able to tune its bandgap,where absorption of visible light is strong to generate hydrogen and oxygen from splitting of water.When N atoms in TiN are partially substituted by O atoms in TNO, the top of the valence band shifts higher compared to the corresponding metal oxide (TiO2) without affecting the level of the bottom of the conduction band.The potential of the HOMO for the oxinitride is located at higher potential energy than that for the corresponding oxide due to the contribution of N 2p orbitals, making the bandgap energy sufficiently small to respond to visible solar light (< 3eV) |
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G60.00312: The Effects of Doping on Small Polaron Formation and Transport in Hematite (Fe2O3) Tyler Smart, Jing Zhang, Bin Yao, Yat Li, Yuan Ping
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G60.00313: Molecular Engineering of Conjugated Polymers for Efficient Hole Transport and Defect Passivation in Perovskite Solar Cells Tao Wang Organic-inorganic hybrid perovskite solar cells represent an exceptional candidate for next-generation photovoltaic technology. However, the presence of surface defects in perovskite crystals limits the performance as well as the stability of perovskite solar cells. We have employed a series of carbazole and benzothiadiazole (BT) based donor-acceptor copolymers, which have different lengths of alkoxy side-chains grafted on the BT unit, as the dopant-free hole transport materials (HTMs) for perovskite solar cells. We demonstrate that although these side-chains can reduce the p-p stacking structural order of these copolymers to affect the hole transport properties, the methoxy unit introduces a desired defect passivation effect. Compared to the Spiro-OMeTAD-based device, the copolymer with methoxy side-chains on the BT unit (namely PCDTBT1) as the HTM achieved superior power conversion efficiency and stability due to efficient hole transport and the suppression of trap-induced degradation, whilst the copolymer with octyloxy side-chains on the BT unit (namely PCDTBT8) as the HTM lead to poor performance and stability. |
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G60.00314: Conformal Solid State Li7La3Zr2O12–PEO-LiClO4 Composite Electrolyte for Advanced Lithium Batteries Parisa Bashiri, Gholam Abbas Nazri, Vaman Naik, Ratna Naik Lithium Ion Battery (LIB) has dominated the field of energy storage devices due to its high energy density and high power delivery. However, there are major safety concerns associated with organic liquid electrolytes currently used in Li-ion batteries. In order to mitigate the problem, the concept of all solid-state battery has been developed. The application of solid electrolyte in practical cells has been hindered by its high electrode/electrolyte interface impedance and the low ionic conductivity of this class of electrolytes. In this research, we have investigated a garnet type super Li-ion conductor Li7La3Zr2O12 (LLZO) compounded with polyethylene oxide containing LiClO4 as a solid electrolyte. We have synthesized LLZO with sol-gel method and casted LLZO/PEO-LiClO4 composite film with ~100 μm thickness with different LLZO concentration (0%-80%). The composite film conductivity was measured using Electrochemical Impedance Spectroscopy (EIS) in the range of 10 mHz to 100 kHz, with Ni blocking electrodes. The electrolyte with 50 w% LLZO content showed higher Li-ion conductivity (~ 10-6 S/cm) at room temperature compared to other concentrations. Vibrational spectroscopy has been employed to investigate the role of LLZO on polymer crystalline phase. |
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G60.00315: Hydrothermal growth of LiFePO4 'nano-seeds' directly on multi-walled carbon nanotube paper as cathode materials for lithium-ion batteries Hamda Al Shibli, Tawaddod Alkindi, Amarsingh Kanagaraj, Rahmat Susantyoko, Boo Hyun An, Saif Al Mheiri, Daniel Choi Nanocomposite of LeFePO4/Multi-walled carbon nanotubes (MWCNTs) was prepared as cathode materials for Lithium ion batteries. First, a sheet of MWCNTs, so called ‘Buckypaper’ with uniform thickness was prepared by surface-engineered tape-casting technique which enables fabrication of strong stand-alone structured carbon nanotube (CNT) sheet with tunable thickness and composition. Secondly, LiFePO4 nano-seeds were grown on the surface of the MWCNTs by hydrothermal process. It was found that nanometer-scale LiFePO4 ellipsoids with good crystal quality were grown on the MWCNTs sheet and uniformly distributed. Size and distribution density of the LiFePO4 nano-seeds were controlled by the experimental conditions such as mixing ratio of precursor chemicals, temperature and time of hydrothermal process as well as pre-treatment of MWCNT sheets with Oxygen plasma. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy were used to characterize the nanocomposite composed of LiFePO4 nano-seeds on MWCNT sheet. The electrochemical characterization of the cathode of LiFePO4/MWCNTs is in progress using a CR2025-type coin cell with lithium foil and anode. |
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G60.00316: A New Phase Diagram of Water under Negative Pressure: The Rise of The Lowest-Density Clathrate s-III YINGYING HUANG, Chongqin Zhu, Jijun Zhao, Xiao Zeng Depending on the surrounding environment (temperature and pressure), ice alone exhibits an exceptionally rich and complicated phase diagram with 18 known crystalline polymorphs. Water molecules also form clathrate compounds with inclusion of guest molecules, such as cubic structure I (s-I), cubic structure II (s-II), hexagonal structure H (s-H), tetragonal structure T (s-T), and tetragonal structure K (s-K). Recently, guest-free clathrate structure II (s-II), also known as ice XVI located in the negative-pressure region of the phase diagram of water, is synthesized in the laboratory and motivates scientists to reexamine other ice clathrates with low density. Using extensive Monte Carlo packing algorithm and dispersion-corrected density functional theory optimization, we predict a crystalline clathrate of cubic structure III (s-III) composed of two large icosihexahedral cavities (8668412) and six small decahedral cavities (8248) per unit cell, which is dynamically stable by itself . A new phase diagram of water ice with TIP4P/2005 model potential is constructed. The guest-free s-III clathrate with ultralow density overtakes s-II and s-H phases and emerges as the most stable ice polymorph in the pressure region below −5834 bar at 0 K and below −3411 bar at 300 K. |
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G60.00317: Pulse Charging Strategies in Lithium Metal Batteries Daniel Jacobson, Thomas Miller Pulse charging has been shown to suppress dendrite formation in lithium metal batteries. This phenomenon was discovered using a computational particle based reaction-diffusion model and later validated experimentally. Pulsing gives lithium ions more time to diffuse before they react with the electrode surface resulting in more uniform deposition. The comparative benefit of pulse charging versus constant voltage charging, however, has not yet been analyzed within this theoretical framework. We propose a new measure of efficacy that defines the most effective charging strategy to be the one that yields the lowest level of dendrite intensity for a fixed charging time. Application of this efficacy criteria to the simplified reaction-diffusion model of the charging process used previously allows the merits of a variety of different charging strategies to be evaluated. |
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G60.00318: Role of alloying in metal clusters reactivity for lithium-air batteries karima lasri, Kah Chun Lau, Khalil Amine, Abdelkader Kara It was shown that the rate of LiO2 formation can be controlled by the size of silver clusters, in connection with lithium-air batteries [1]. A gap at the fermi level was found to control the rate of oxygen reduction at the cathodes [1]. The present study tackles the effects of alloying in the electronic properties of small clusters adsorbed on a hydroxylated alumina surface. Starting from a pristine Pd5 cluster with a 0.32 eV HOMO position from the fermi level, we show that this gap can be controlled by alloying, resulting in a reduction to about 0.15 eV when alloying (single atom) using Ni or Mn. Alloying using a Ru atom resulted in an increase in the HOMO position to 0.49 eV, while for Ag, Au, Pt and Co, this value was found to be 0.2, 0.2, 0.23 and 0.36 eV, respectively. These preliminary results show that alloying may be used to tailor the gap at the fermi level in metal clusters. Results for different levels of stoichiometry (x) as well as different sizes (N) of PdN-xMx will be presented. |
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G60.00319: First-principles calculation of discharge reaction products in Na/SnS batteries Hiroki Kotaka, Tamio Oguchi, Hiroyoshi Momida, Ayuko Kitajou, Shigeto Okada Li-ion batteries have been widely used as power sources in mobile electronics devices because of their high energy density. To extend them to much wider usage, it is necessary to develop batteries without high-cost rare-metals such as Li and Co. Recently Na-ion batteries have been highly recognized as one of the next-generation secondary batteries, in which high-cost Li is replaced with ubiquitous Na. As an anode material suitable for Na batteries, we focus our attention on tin compound SnSx. Possible reaction products such as ternary Na-Sn-S and binary Na-Sn systems during the discharge reaction processes are searched by using a crystal structure prediction tool and the electrochemical properties are evaluated from first principles. Voltages of Na/SnS discharge process are calculated and compared with experiments. To clarify the phases of intermediate products, x-ray absorption spectra are computed by applying Fermi golden rule for calculated electronic structure with explicit core hole. |
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G60.00320: Atomic Sulfur Anchored on Silicene, Phosphorene and Borophene for Excellent Cycle Performance of Li-S Batteries Fen Li, Jijun Zhao For the first time, atomic sulfur is incorporated into silicene, phosphorene and borophene to intrinsically eliminate the dissolution of LiPS. A high atomic sulfur coverage (63.1 wt%) is achieved in silicene and concomitantly stabilizes the silicene layer. For the S3-covered silicene, a high theoretical capacity of 857 mA h g-1 is achieved with slight dissolution of LiPS originated from the loss of interior S atoms that are not directly bound with silicene surface. By realizing the elemental S2 coverage on silicene with large surface area, the Li+ ions can react fast with the S2 species, leading to a high theoretical capacity of 891 mA h g-1 without dissolution and migration of the intermediate LiPS. Most interestingly, the discharge products of atomic layer of lithium sulfides on silicene surface exhibit completely different behaviors with the traditional discharge products of solid Li2S, which can function as effective adsorption and activation sites for the conversion of LiPS from long-chain to short-chain by accelerated redox reaction. The present study gains some key insights into how the atomic sulfur contributes to the intrinsic shuttle inhibition and offers a feasible way to design the atomic sulfur based cathode of Li-S batteries with better electrochemical performance. |
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G60.00321: New insights on the structural formation of polyanionic phosphate compounds revealed by new Mossbauer and XRD measurements karima lasri, Abdelfattah Mahmoud, My Rachid TIGHA, Moulay Tahar Sougrati, Raphaël P Hermann, Abdelkader Kara, Khalil Amine The exploration of optional electrode materials for lithium and sodium ion batteries, still an active field with continuous research efforts. Based on several advantages, polyanionic phosphate compounds M0.5TiOPO4 (M= Fe, Ni, Co, Cu), as negative electrode materials of Lithium-ion batteries, were the subject of a limited number of experimental studies. |
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G60.00322: Ab initio studies of aluminium insertion into amorphous vs crystalline VO2 : improvements in voltage and energy density Sergei Manzhos, Vadym Kulish, Daniel Koch Vanadium oxides (VO) are among the most promising materials that can be used as electrodes in multivalent rechargeable batteries. VO can be used as electrode materials for Al ion batteries although voltages reported to date are rather low, leading to low energy density. We explore amorphization as a strategy to increase voltage and compare Al insertion into amorphous vs crystalline VO2 . The amorphous structure is generated using a customized force field, and Al insertion is then studied by first-principles calculations. We show Al insertion in amorphous VO2 can occur at insertion sites with well-dispersed insertion energies, with the lowest energy site much more thermodynamically favourable than any insertion site in the crystalline VO2. We compute the voltage-composition profile for amorphous VO2 and show that amorphization increases the average voltage of VO2 cathode, which will lead to higher energy density. We also suggest that the stability of amorphous VO2 cathode is improved by reducing volume expansion during Al insertion, potential leading to longer cycle life in practical applications. Overall, the demonstrated improvements suggest a high potential of amorphous VO2 electrodes for multivalent batteries. |
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G60.00323: Solvation Dynamics of Lithium-Sulfur Electrochemical Reaction Systems Lihua Xu, Fredy Aquino, Chengyin Fu, Bryan Wong, Juchen Guo Li-S dissolution during charge-discharge process presents a fundamental dilemma in the design and fabrication of Li-S batteries. Hence, new paradigms of solid-state Li-S electrochemical reaction mechanism enabled by sub-nano confinement of sulfur are being explored. A great advantage of this mechanism is its compatibility with different types of electrolytes. However, the solvation energy and structure also play important roles in this mechanism. In this poster, we investigate the solvation effects of the Lithium bis(trifluoromethanesulfonyl)imide(Li[TFSI]) electrolyte based on various ether solvents, such as mono-(G1), di-(G2), tri-(G3), tetra-glyme(G4), 15-Crown-5(G5), using classical and ab initio MD simulations. Specifically, we analyze in detail the solvation shell around the Li-ion as well as the binding energy per Li-ion. Our results show that depending on the type of solvent considered, different number of molecules are required to form a stable solvent shell around the Li-ion. In addition, we note that the G5 solvent forms the most stable solvation shell amongst all the solvents. Our simulation model gives the results which are in excellent agreement with experimental observations. |
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G60.00324: First principle study of Na3SbS4 superionic conductor under pressures Ming Yu, Hui Wang Pressure induced structure changes and even phase transitions will significantly affect the conductive and mechanical properties of Na3SbS4 superionic conductor. We performed a systematic study on this issue employing density functional method. Our preliminary results revealed that the tetragonal crystalline structure could transform to the cubic phase along some pathways even under low pressures. The energy barrier of Na atoms diffusing in the cubic structure, on the other hand, will be lowered by decreasing pressure, and the halide anion doping will affect the diffusion of Na atoms in Na3SbS4 superionic conductor. |
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G60.00325: PVDF-HFP + Carbon Nanofiber as a Functional Interlayer for Long-Life Lithium-Sulfur Batteries Anyi Zhang, Xin Fang, Chenfei Shen, Yihang Liu, In Gi Seo, Yuqiang Ma, Liang Chen, Patrick Cottingham, Chongwu Zhou Recently, lithium-sulfur (Li-S) battery has become increasingly attractive due to the high theoretical specific capacity (1675 mAh g-1) and energy density (2567 Wh kg-1). In addition, the cost can also be reduced dramatically because S is abundant in the Earth crust. In the present work, we have developed a scalable and inexpensive design for lithium-sulfur (Li-S) batteries by capping a flexible gel polymer / carbon nanofiber (CNF) composite membrane onto a free-standing and binder-free CNF + Li2S6 cathode, thus forming a three-dimensional (3D) structural design. While the CNF network was used as the current collector and S holder to overcome the insulating nature and volume expansion of S, the composite membrane composed of a gel polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and CNF additive was used as an interlayer to trap polysulfides and recycle remaining S species, leading to high specific capacity and long cycle life. This 3D structure enables excellent cyclability for 500 cycles at 0.5 C with a small capacity decay of 0.092% per cycle. Furthermore, outstanding cycle stability has also been achieved at even higher current densities (1.0 C - 2.0 C), indicating the great promise for practical applications of Li-S batteries. |
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G60.00326: Plasma Activation for Enhanced Seed Germination and Growth in Hydroponics Valentina Lee, Edbertho Leal-Quiros A significant increase in nonthermal atmospheric plasma applications, such as dielectric barrier discharge (DBD) plasmas, have been steadily increasing in industry and in the research literature. DBD plasmas have shown immense potential in accelerating and enhancing germination and growth characteristics in a variety of plant seeds. Enhancing germination and growth in hydroponic species may have significant benefits to future space habitats. Experiments are conducted to investigate the effect of DBD plasma treatment of several different common hydroponic seed species with various parameters demonstrating enhanced seed germination and growth compared to untreated control groups. The parameters being investigated in the experiments include plasma device characteristics such as voltage, current, and frequency, as well as other significant parameters such as displacement between seed and DBD source, treatment time, and temperature of the plasma. Plasma is applied to deionized water and the seeds separately as well as concurrently. Germination and growth characteristics are determined by stem height and final mass. Seeds are grown hydroponically in a controlled environment with deionized water. Different types of energy are also applied and compared with DBD plasma treatment. |
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G60.00327: Modeling of a bi-phasic process for the dehydration of xylose from biomass: Effects of solvents on the process cost Geunjeong Lee, Byeonghyeon So, Jeong-Myeong Ha, Myung-June Park The present study addresses the dehydration of xylose, available from biomass, to obtain furfural. To enhance the reaction, additional solvent, highly selective to furfural, is used to develop a bi-phasic process. Although chloroform, methyl isobutyl ketone (MIBK), and toluene have been usually considered as effective solvents, they are also known as environmentally unfriendly and toxic chemicals. As an alternative, 2-pentanone is suggested since the material is one of by-products in downstream processes and shown to be used as inert materials. Because the partition coefficient is relatively low compared to chloroform and MIBK, process cost is expected to increase. In this study, a process, composed of bi-phasic reactor and separation units, is considered and the effects of solvents on the process costs are evaluated. Thermodynamic analysis and process simulation showed that, despite relatively low partition coefficient, the degree of increase in a 2-pentanone-based process is insignificant, while guaranteeing the benefit of eco-friendly process. |
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G60.00328: External Electric Field Driving the Ultra-low Thermal Conductivity of Silicene Guangzhao Qin, Ming Hu Manipulation of thermal transport (pursuing ultra-high or ultra-low thermal conductivity) is on emerging demands, since heat transfer plays a critical role in enormous practical implications. It is well established that the thermal transport in semiconductors can be effectively modulated by structure engineering or materials processing. However, almost all the existing approaches involve altering the original atomic structure, which would be frustrated due to either irreversible structure change or limited tunability of thermal conductivity. Motivated by the inherent relationship between phonon behavior and interatomic electrostatic interaction, we comprehensively investigate the effect of external electric field, a widely used gating technique in modern electronics, on the lattice thermal conductivity (k). Taking two-dimensional silicon (silicene) as a model system, we demonstrate that, by applying electric field (Ez = 0.5 V/Å) the thermal conductivity of silicene can be reduced to a record low value of ~0.091 W/mK, which is more than two orders of magnitude lower than that without electric field (19.21 W/mK). |
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G60.00329: Use of Convex Optimization to Increase Energy Efficiency of Plug-in Hybrid Vehicles John Fox, Jason Platt, Nicholas Moehle We investigate the method of convex optimization to improve the efficiency and resource utilization of Plug-in Hybrid Electric Vehicles (HEVs). Our optimization uses information about a known or estimated vehicle route to predict energy demands and maximally use grid-sourced electricity and minimally use petroleum resources for a given route. Our convex optimization method uses a simplified car model to find the optimal strategy over the whole route, which allows for re-optimization on the fly as updated route information becomes available. The approach allows a vehicle to use only electric-drive on a designated portion of the route, for example to traverse an urban area with electric drive requirements. Validation between the simplified model and a more complete vehicle technology model simulation developed at Argonne National Laboratory was accomplished by “driving” the complete car simulation with the simplified control model. By driving on routes with the same total energy demand but different demand profiles the preliminary results show efficiency gains of 5-15% on mixed urban/suburban routes compared to a Charge Depleting Charge Sustaining (CDCS) battery controller. |
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G60.00330: Ultrasmall Angle X-ray Scattering (USAXS), Wide Angle X-ray Scattering (WAXS), and Raman Studies on the Complex Metal Hydride NaAlH4 Tabbetha Dobbins, Christopher Bennett, James Torres, Jan Ilavsky This research seeks to understand the role of ScCl3, ZrCl4, and VCl3 catalysts in NaAlH4 by examining these hydrides at multiple length scales using an X-ray scattering instrument which is capable of simultaneously measuring scattering wave vector, Q, of 0.0001Å-1 to 6.0 Å-1. Isothermal studies were performed at 30oC, 65oC, 100oC, 135oC, and 170oC. Results show an increased surface area as temperature increased for all doped samples (and milled). Pore size remains relatively constant with temperature. Doped samples show 70-80nm pore sizes while milled is smaller. At 135oC, there is little change in surface area or radius of gyration (Rg) for all samples. The number of pores in the 50-70nm size range increases with both temperature (T) and time (t). Raman and WAXS data show no product phase and so the changes in pore structure are occuring before measurable hydrogen desorption occurs. |
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G60.00331: Maximizing Physisorption of Hydrogen by Metal-Doping of Graphene Derived Carbon Ariel Hasse, Hillary Smith, Nicholas Weadock, Channing Ahn, Brent Fultz Hydrogen, as a fuel for fuel-cell vehicles, is limited by the ability to densely pack large quantities of hydrogen at low pressures. Material-based storage using graphene as an adsorption substrate is a promising alternative as the hydrogen gas can interact with the graphene planes by weak Van der Waals forces. Graphene is lightweight and has a surface area of 2630 m2/g and hydrogen can be reversibly adsorbed on the graphene through physisorption, potentially allowing an increase in volumetric hydrogen density over other carbon sorbents. This research seeks to further maximize hydrogen adsorption onto graphene through decoration of the carbon surface with metals. Graphene derived carbon was functionalized with varying amounts of nickel and copper metals. The size and amounts of metal clusters was analyzed with scanning electron microscopy and x-ray fluorescence. We found a 15 to 20 percent increase in hydrogen adsorption over pristine material for a copper-functionalized material with 2285 m2/g surface area and a nickel functionalized material with 2325 m2/g at room temperature and 1 bar. |
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G60.00332: GENERAL THEORY/COMPUTATIONAL PHYSICS
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G60.00333: Time propagation method for the coupled Maxwell and Schrodinger equations on the same atomistic Haley Buckner, Cody Covington, Daniel Kidd, Kalman Varga We implement a semi-classical, hybrid simulation to investigate the interaction of electromagnetic fields and matter on the atomic scale using Density Functional Theory (DFT) calculations coupled to Maxwell’s equations. We present two approaches to simulate the time propagation of the Maxwell equations on the atomic scale, using a simplified quantum mechanical system, jellium, as the target for the incident electromagnetic pulse. The first approach implements finite difference time domain, which employs finite differences as approximations to both spatial and temporal derivatives that appear in Maxwell’s equations. However, FDTD is shown to be numerically unstable, so a new method must be implemented. The second approach implements the Riemann-Silberstein vector, a complex vector composed of the electric and magnetic fields, to propagate Maxwell’s equations. Using the Riemann-Silberstein formalism, we can track both the Maxwell and Schrodinger equations on the same atomistic scale and observe induced excitations in jellium. The next step is to use real atoms and nanostructures in place of jellium as the target of the electromagnetic pulse. |
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G60.00334: 3D Registration in a Virtual Reality Simulator for Neurosurgical Instruction Ted Dorfeuille, Andrew Pounds Virtual Reality and computer graphics techniques have been used since their inception in numerous medical professions and it has long been thought that the technology would be ideal for training simulations. A recent review article noted that simulators for neurosurgery containing completely immersive environments and realistic touch response were particularly lacking. This project attempts to utilize commercial gaming headsets with a mechanical haptic feedback device to simulate surgery in an immersive environment with touch feedback. The focus of the current research is the use of 3D registration techniques and basis set transformations to map the space of the 3D models in the VR environment to the physical models and surgical instruments that might be in the hands of the operator. |
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G60.00335: A Generalized Antiferromagnetic Model for Bonding Electrons Chun-feng Huang, I-Hsun Tsai The antiferromagnetic (AF) density matrix is generalized for bonding electrons. The covalent-correlation operators are constructed based on the energy contribution of the two AF parts in the covalent component, and the density-fluctuation operators are introduced to include the charge variation resulting from the coexistence of the ionic and covalent components. Under the adjacent hopping, the effective mass tends to infinity in the covalent limit just as that in the Mott insulator. On the other hand, the effective mass becomes finite when the ionic component coexists with the covalent one. By extending the density matrix, a family of random-hopping Hamiltonians can be taken into account for the disorder-induced insulating behaviors under such coexistence. Therefore, our study reveals a unified way to understand different insulating behaviors. |
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G60.00336: Constraining New Physics in Lepton Flavor Universality Anomalies with LHC data using ATOM. Cheyenne Nelson, Michele Papucci Searching for physics beyond the Standard Model at high energy colliders requires an enormous investment in resources and time. Frequently these searches are applicable to test a broader range of theoretical models than they were originally designed to test. The reinterpretation of experimental results imparts a broader impact to a given search while not requiring the further reprocessing of data. Our research presents the usage of a newly developed software framework for reinterpretation, ATOM, the Automated Test of Models. ATOM was applied to the reinterpretation of Z’, W’ and leptoquarks searches from the ATLAS experiment. Because of recent anomalies in lepton flavor universality measurements in heavy flavor decays, an evaluation of theoretical models that seek to account for these anomalies is of interest to the particle physics community. ATOM was thus used to evaluate viable models that endeavor to explain these heavy flavor anomalies by testing their relative correlation with experimental data from ATLAS. |
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G60.00337: Substrate effect on excitation dynamics of 2D materials Subodh Tiwari, Hiroyuki Kumazoe, Aravind Krishnamoorthy, Fuyuki Shimojo, Rajiv Kalia, Aiichiro Nakano, Priya Vashishta Excitation dynamics of 2D materials has been extensively studied by different theoretical and experimental methods. However, effect of substrate on the excitation dynamics of 2D materials has not been well delineated. We perform quantum molecular dynamics simulations at high electron temperatures within the density functional theory framework to understand the effect of substrate. The simulation results show that interaction between substrate and transition metal dichalcogenide layers create distinct anisotropy in electronic excitation-induced lattice dynamics that may be experimentally observable. |
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G60.00338: Angle-resolved photoemission spectroscopy from first-principles quantum Monte Carlo Matteo Barborini, Sandro Sorella, Massimo Rontani, Stefano Corni Angle-resolved photoemission spectroscopy (ARPES) allows to visualize in momentum space the probability weight maps of electrons emitted from molecules deposited on a substrate1. Within the plane wave approximation, these maps can be reproduced through the square modulus of the Fourier transform of the hole-quasi-particle wave function (hQPWFs), also known as Dyson orbital, associated to the electron that is photoemitted2,3. The QPWFs naturally include all the correlation effects between the electrons involved in the process. On the other hand, the interpretation of these maps usually relies on the plane wave approximation, through the Fourier transform of single particle orbitals obtained from Density Functional Theory (DFT). Here we propose a many body approach based on quantum Monte Carlo (QMC) to directly calculate the hQPWFs of molecules in momentum space, reproducing ARPES data. Through the comparison between these correlated QMC images and their single particle counterparts, we visualize features that solely arise from many-body effects. |
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G60.00339: Particle Shape Effects in Vibrational Electron Energy-Loss Spectroscopy David Kordahl, Christian Dwyer Vibrational spectra in the scanning transmission electron microscope are strongly influenced by the shape of the sample being studied. We explore these shape effects using the local phenomenological model of Born and Huang. We quantize this model and characterize the general properties of its harmonic modes to simulate electron energy-loss spectra from several regular geometries (foil, cylinder, sphere, prolate and oblate spheroid). We then extend these methods to the vibrational modes and surface plasmons of irregularly shaped particles. Finally, we show how vibrational modes of a surface molecule coupled to the surface plasmons of a metallic nanoparticle can yield Fano-type spectral profiles. |
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G60.00340: Electrical control of inter-layer excitons in van der Waals heterostructures Andrey Chaves, Javad Azadani, Ongun Ozcelik, Roberto Grassi, Tony Low We investigate excitons in stacked transition metal dichalcogenide (TMDC) layers under perpendicularly applied electric field, herein MoSe2/WSe2 van der Waals heterostructures [1]. Band structures are obtained with density functional theory calculations, along with the electron and hole wave functions in conduction and valence bands, respectively. Although the type-II nature of the heterostructure leads to fully charge separated inter-layer excitons, charge carriers distribution among the layers is shown to be easily tunable by external field. Our results show that moderate values of electric field produce more evenly distributed wave functions along the heterostructure, thus enhancing both the inter-layer exciton binding energy and, most notably, its oscillator strength. |
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G60.00341: Ab initio study of water speciation in forsterite TIAN QIN, Renata Wentzcovitch, Koichiro Umemoto Water or hydrogen in the Earth’s mantle can be stored as hydrous defects in nominally anhydrous minerals (NAMs). Although in modest concentrations, these defects change the physical properties of their hosts, including electrical conductivity and viscosity, properties that affect mantle processes such as convection. To understand the influence of water on mantle properties, the mechanisms of water incorporation in olivine, the most voluminous mineral in the upper mantle, must be determined. The most likely incorporation mechanism of hydrogen in olivine is substituting for Mg and Si cations. However, a long-standing debate remains concerning the relative thermodynamic stability of these defects. |
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G60.00342: Machine Learning the Gibbs Energies of Inorganic Crystalline Solids Christopher Bartel, Samantha Millican, Ann Deml, John Rumptz, Bill Tumas, Alan Weimer, Stephan Lany, Vladan Stevanovic, Charles Musgrave, Aaron Holder The drive to rapidly predict, screen, and optimize materials using first-principles calculations has led to large datasets and the construction of open-source databases that are populated almost exclusively by temperature-independent density functional theory (DFT) calculations. Although these datasets are an invaluable resource, their predictive ability at finite temperatures is limited and current methods for evaluating the missing temperature dependencies are computationally prohibitive. In this work, we show that compound Gibbs energies of formation can be predicted with accuracy comparable to the quasiharmonic approximation at finite temperatures of up to at least 1800 K and at the same computational expense as a DFT total energy calculation. Implementing our approach on the Materials Project database reveals interesting trends with respect to the stability (and metastability) of inorganic crystalline solids. Specifically, we quantify as a function of temperature the fraction of compounds in the Inorganic Crystal Structure Database (ICSD) predicted to be thermodynamically stable and the magnitude of metastability for thermodynamically unstable structures and identify chemical spaces which are found to have anomalous ranges of accessible metastability. |
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G60.00343: Classical Simulation of Quantum Computations: Application of Matrix Product State Approach to the Compression of DNA Bit Strings George Davila, Eduardo Mucciolo Tensor Networks may be used to describe the entanglement spectrum of Quantum Many-Body (QMB) systems in a manner which tells us about the entanglement between subsystems without loss of the description of the entire system. One such approach for 1D entanglement in gapped systems is the Matrix Product State (MPS) approach. While MPS-derived algorithms give us the entanglement spectrum for a QMB system, they similarly describe correlations, corresponding to various patterns, in more general data sets. The MPS representation of any given set of data will therefore tell us about underlying structures in the data. Data sets which contain dominant patterns (i.e. localized subsystems) are compressible. Random sets (i.e. thermalized systems) are, to the contrary, generally incompressible. Not only can compressible systems be stored more compactly, but they also have polynomial-sized Hilbert space representations (complexity class P), and thus may be constructed (or deconstructed) via a finite quantum circuit array in polynomial time. Here we construct MPS representations for samples of DNA. We show that individual genes are relatively randomly structured and that one can exploit the properties of DNA so as to compress combinations of samples from multiple members of a given species. |
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G60.00344: Predicting Material Properties by Integrating Combinatorial Experiments, Ab-initio Calculations, and Machine Learning in the FexCoyNi1-x-y Ternary Yuma Iwasaki, Ichiro Takeuchi, Masahiko Ishida Combinatorial experiments allow rapid mapping of composition-structure-property relationships across large compositional phase space. There are, however, physical properties which are difficult to perform rapid quantitative mapping. For instance, it is nontrivial to extract detailed information regarding spin and orbital magnetic moments of compounds in composition spreads. We propose an alternative approach which combines combinatorial experimentation, ab-initio calculations, and machine learning. In order to decipher the detailed magnetic properties across Fe-Co-Ni composition spread, we perform structural phase distribution mapping of the spread by X-ray diffraction, use Korringa Kohn Rostoker – Coherent Potential Approximation for ab-initio calculations, and apply non-negative matrix factorization. As a result, the predicted mapping of saturation magnetization by the proposed approach was well-consistent to the mapping of Kerr-rotation in combinatorial magnet-optic Kerr effect experiments. The result indicates that our approach has a potential to enable rapid mapping of more various physical properties by integrating combinatorial experiments, ab-initio calculations, and machine learning. |
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G60.00345: Mapping Electronic Structure to Coarse-Grained Degrees of Freedom via Supervised Machine Learning Nicholas Jackson, Alec Bowen, Daniel Reid, Venkatram Vishwanath, Juan De Pablo The modeling of photoactive soft materials typically involves the synthesis of classical and quantum mechanical simulation protocols to capture the impact of nuclear degrees of freedom on the electronic structure of the material. For these systems, the sampling of configuration space is often a substantial computational bottleneck warranting the use of computationally-cheaper coarse-grained models. However, these coarse simulations must be followed by a backmapping of the atomistic coordinates, as well as electronic structure calculations for each configuration, in order to accurately describe the material's electronic structure. Here, we present a simulation protocol for mapping configuration-dependent electronic structure directly to coarse-grained nuclear degrees of freedom over multiple length scales using techniques from supervised machine learning. We describe the impact of this approach on the acceleration of simulations, as well as the potential ability to discover coarse-grained representations relevant to organic semiconductors. |
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G60.00346: Machine Learining of Few-Body Scattering Problem Yadong Wu, Pengfei Zhang, Huitao Shen, Hui Zhai One of a basic problem in few body scattering physice is solving the scattering length while we know details of scattering potential. We propose a new method to solve scattering length based on neural network. Using a two hidden layer fully-connected neural network, we can see it works very well to solve this problem. After training we open the neural network and see how it works while training potential is santisfied perturbation theory. We see it does first and second order Born-Approximation while potential strength is very shallow. |
(Author Not Attending)
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G60.00347: The Necessity and Freedom of Artificial Intelligence Kenneth Beck, Kelli Lee, Brianna Lee What necessity drives AI? What freedom is derived? |
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G60.00348: Interaction between Flexible Structure and Compressible Flow Hiroharu Matsubara, Yohei Inoue, Hiroshi Maekawa We have developed a strong-coupling solver with immersed boundary method (IBM) to solve the fluid-structure interaction for flexible structure: especially a fluid compressibility is taken into account. In recent years, it attracts attention that more flexible structure than traditional rigid one being used for propulsion mechanism and control method in wing of airplanes, flapping robots. Also, we know that there is time scale gap between fluid and solid motion. So it is important to consider the time scale gap between fluid and solid motion adequately in developing numerical method for fluid structure interaction with flexible body. This research aims to contribute to the application such as the reduction of aircraft vibration. As this solver performs the calculation in orthogonal lattice of Cartesian coord system, calculation cost could be reduced as compared with strongly coupled fluid-structure analysis software using conventional Finite Element Method (FEM) for fluid calculation. Using the developed solver, we analyzed fluid flow and flexible structure to change shape from the initial state and flow field, and examined the numerically behavior of interactions. We made sure the behavior of the solver and confirmed the effectiveness of consideration the time scale gap. |
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G60.00349: Studying XY-like critical phases using tensor-network renormalization Nicholas Pomata, Ching-Yu Huang, Tzu-Chieh Wei The development of 2D tensor renormalization techniques capable of isolating short-range correlations, such as Evenbly and Vidal's tensor network renormalization (TNR) and Yang, Gu, and Wen's loop-TNR, offers us non-perturbative numerical tools to analyze long-distance behavior of systems with large or infinite correlation length. We test these methods on systems with continuously-varying criticality, in particular, systems which behave in the infrared as a c=1 free-boson CFT. Exactly-solved models with this property, in particular the six-vertex model and the spin-½ XXZ chain, allow us to benchmark the precision of these methods. We also examine classical ZN spin models, which are not exactly solvable but which are known to have "soft" phases with physics resembling that of the low-temperature XY model. We study these phases and interpret our results in light of their Kramers-Wannier duality, using methods developed by Hauru et al. (2016). |
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G60.00350: Simulations of an off-lattice model for polymers doubly grafted to a homogeneous substrate Shengming Zhang, Michael Bachmann Conformational phases of an off-lattice flexible homopolymer model with both ends attached to |
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G60.00351: Applied Networking Technology in Explorational Research Juan Ramirez Chavez, Arijit Das In this period of the technological era, ongoing research has been devoted to adapting and utilizing networking tools for the purpose of allowing greater connectivity between various, independently-run components to achieve the tasks of a unified system and thereby conduct research in locations where the economics of operating an autonomous vessel are cost-efficient. Throughout this investigation, two projects were conducted to validate questions regarding distributive data analysis. First, research was done on Simrad 4G radar and RTI IntegRadar XIR3000 radar system integration using Robotic Operating System (ROS) as a method of processing navigational information to a database with TCP and JavaScript websockets. Second, research was done on a 3-server setup running Red Hat Enterprise Linux with Cloudera's Manager Hadoop configuration software which allows for high-performance computing based on powerful data distribution. Regarding the ROS research, our results indicate that enabling communication between the two components is possible using TCP/IP and web socket protocols in order to transfer data to be analyzed. |
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G60.00352: Predicting the Morphology of β-HMX Crystal using Molecular Dynamics Study Seulwoo Kim, Bumjoon Seo, Minhwan Lee, Won Bo Lee The growth habit of β-HMX crystals grown from acetone has been characterized with (020), (011), (110) and (101) faces both from experimental and theoretical studies. In the present work, this growth habit is elucidated with the spiral growth mechanism, which is the dominant growth mechanism at low supersaturations. For the external habit controlling factors in the model, we suggest a generalized interfacial structure analysis model to account for the effects of both the anisotropic local concentrations of the growth units at the interface and the free energy barriers for reorientation of the growth units. In order to compute the free energy surfaces, we used metadynamics with molecular order parameters as the collective variables to identify the orientation and conformation of the adsorbed growth unit. The predicted morphology of β-HMX through our approach implies the significance of the role of anisotropic local concentrations on the relative growth rates of the slow growing faces. |
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G60.00353: Interfacial Structure Analysis for the Morphology Prediction of Adipic Acid Crystals from Aqueous Solution Minhwan Lee, Bumjoon Seo, Seulwoo Kim, Won Bo Lee, Youn-Woo Lee In aqueous solution, adipic acid crystals have a hexagonal plate morphology with a dominant (100) face, where the hydrogen-bonding carboxylic acid groups are exposed. In the present work, the crystal morphology was investigated by interfacial structure. The key external habit-controlling factor turned out to be the concentration of effective growth units at the interface by molecular dynamics simulations at the crystal−solution interface. The differences of two factors from the interfacial structure analysis that determine the concentration of the effective growth units explained why faces of (002), (100), and (011) are experimentally observed and faces of (11-1), (10-2), and (20-2) are not. The observed faces were characterized by larger values of both the surface molecular orientation factor and scaling factor, high free energy barriers for reorientation on these faces and implying low anisotropic local concentrations at the interface, respectively. Furthermore, factors of spiral geometry were incorporated into the original approach which resulted in a close resemblance to the experimental morphology. |
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G60.00354: Simulations of an immersed sheet in a fluid Landon Johnson Examining the dynamics of an immersed sheet in a fluid provides experimental data on the elastic properties of this sheet. These experimental results inspire our development of a coupled MD model for the sheet coupled to a lattice Boltzmann method for the fluid flow. In this poster I will present initial results on the development of an immersed boundary lattice Boltzmann method that can be used to analyze the experimental results for the deformation of such a sheet. |
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G60.00355: Modeling of Square ZnO Nanomembrane with Two Types of Cavities: Vacuum Cavity and Graphene Cavity Using Comsol Multiphysics Software: The Case Study MEMS Capacitive Pressure Sensor Ahmad Alsaad, Ahmad Ahmad, Qais AL-Bataineh We propose the modeling of Micro-Electro-Mechanical Systems (MEMS) capacitive pressure sensor. Two kinds of Nano-membranes were investigated. Mainly ZnO/Vacuum/SiO2/Si and ZnO/Graphene/SiO2/Si capacitive sensors were studied using COMSOL Multiphysics. Capacitance, deflection versus pressure for various membrane thicknesses were modeled and simulated using Finite element method (FEM). The total, average, and maximum deflection as a function of applied pressure were studied. We found that deflection increases as the applied pressure is increased. The average displacement, total displacement, mechanical sensitivity and capacitance sensitivity for both cavities were found to be the same. However, the capacitance of the capacitor formed using graphene cavity is larger than that of the capacitance obtained using vacuum cavity. Our results could be used as guides to design such novel capacitive sensors. |
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G60.00356: Inversion of electron microscopy images using atomistic simulations and machine learning Eric Schwenker, Fatih Sen, Spencer Hills, Maria Chan Atomic structure of materials can be characterized by transmission electron microscopy (TEM) and scanning TEM (STEM). However, determining the positions of atoms in three dimensions from two-dimensional images is non-trivial. In this work, we use atomistic modeling with first principles density functional theory (DFT) or empirical potentials, in conjunction with machine learning, to tackle the S/TEM image inversion problem. We discuss the use of single and multi-objective evolutionary and basin-hopping approaches for S/TEM-guided atomistic structure determination, incorporating comparison of simulated and experimental S/TEM images using computer vision approaches. We show that the combined use of energetic and experimental information is effective in arriving at physical solutions. |
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G60.00357: First-principles study of monolayer Co adsorption on monolayer MoS2 Wuzhang Fang, Po-Hao Chang, Kirill Belashchenko Functionalization of two-dimensional materials by using the magnetic proximity effect could be utilized for spin injection and detection in spintronic devices. Here we study the adsorption of a monolayer of cobalt on monolayer MoS2 using first-principles calculations and the LDA+U method. The preferred adsorption site is on top of Mo for small U and on top of S for U > 4 eV. The value of U calculated using the linear response method is 4.2 eV, and therefore Co is predicted to adsorb on top of S. The ground state is found to be antiferromagnetic. |
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G60.00358: Predicting the densities of amorphous materials through first-principles calculations Yoritaka Furukawa, Yu-ichiro Matsushita First-principles calculations had not ever been performed to predict the densities of amorphous materials. This was due to the fact that because of the disordered nature of amorphous materials, their atomic configurations are completely different from one sample to another, and thus there is no one-to-one correspondence between the densities and the total energies. In preceding reports, in which the densities of amorphous semiconductors were estimated using (semi-) classical molecular dynamics simulations [1], such correspondence was not considered. In our study, to remedy this problem, we have devised a novel method which employs the density functional theory (DFT) and the Car-Parrinello molecular dynamics method. We have applied it to amorphous silicon and found that the determined density and its bulk modulus are in good agreement with experiments. The presented method is expected to be applied to other amorphous systems, including those that are experimentally undiscovered. |
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G60.00359: f-electron structure database (FESD): A high-throughput data analysis and materials discovery tool for strongly correlated materials Hasnain Hafiz, Adnan Khair, Hongchul Choi, Arun Bansil, Towfiq Ahmed We have developed a database with associated high-throughput computational tools for analyzing structural and electronic properties of f-electron materials such as the lanthanide and actinide compounds. Modeling of these systems is especially challenging due to the complex interplay between the effects of spin-orbit coupling, electron-electron interactions and the hybridization of the localized f-electrons with itinerant conduction electrons. This complexity drives richness of electronic properties, making these materials suitable for various technological applications. Here we adopt a data-driven approach to aid the materials discovery process. By deploying state-of-the-art algorithms and query tools, we train learning models using a large, simulated dataset based on existing f-electron crystals. The machine-learned models so obtained can then be used to search for new classes of stable materials with desired physical properties. We discuss the basic structure of our database and our approach toward cleaning and correcting the structure data files. Illustrative examples of the applications of our database include prediction of stable superstructures of double perovskites and identifying a number of interesting trends in strongly correlated features of f-electron based materials. |
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G60.00360: Lattice Dynamics of Polymorphic ZnIn2S4: An Ab Initio Study Jinho Lee, Woosun Jang, Taehun Lee, Aloysius Soon The ternary chalcogenide, ZnIn2S4 is known to exhibit various polymorphic expressions: from the cubic spinel (high pressure) phase to various polytypic layered hexagonal structures, namely the α-, β- and γ-phases. Interestingly, these layer-type structures (α, β and γ) are speculated to exhibit relatively low thermal conductivity but a systematic theoretical description of the lattice thermal conductivity in these van der Waals (vdW) bonded layered of the polytypes is still lacking. Previous theoretical studies have not carefully considered vdW interactions which are dominant in layered materials and to date, only the simple α and spinel phases have been examined. In this work, we systematically perform first-principles density-functional perturbation theory calculations to understand the fundamental lattice properties for all ZnIn2S4 polytypes and propose their potential applications in the next generation thermoelectric devices via solving the Boltzmann transport equation. |
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G60.00361: Molecular Model for the Interaction of Charged Nano-Diamonds with Metal Surface Liangliang Su, Jacqueline Krim, Donald Brenner Prior experiments (Z. Liu, et al., RSC Advances 5, 78933 – 78940 (2015)) suggest that nano-diamond(ND) charge, as measured by the Zeta potential, can have a large influence on tribological performance. Using molecular dynamics simulations, we have characterized the interaction between charged NDs and gold surface in water. Two atomic models of octahedral NDs in water were created that mimic the negative and positive experimental NDs, one with chemisorbed carboxyl groups (COO-) and Na+ counter ions, and one with chemisorbed amino groups (NH3+) and Cl- counter ions. To explore the influence of particle/surface electrostatic interactions, the simulations were carried out with and without induced charges on gold surface. For both types of ND, the induced electrostatic interactions enhance surface adhesion and increase the force needed to slide the NDs along the gold surface. However, the magnitude and mechanism of these effects were found to depend on the ND surface groups. The simulations predict that the positive NDs are both more strongly adhered to the gold (by a factor of almost three), and require a larger force for sliding (by a factor just greater than two). These results are consistent with prior experiments from Liu et al. |
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G60.00362: Ab Initio Study of Electronic and Magnetic Properties of Cobalt Doped AlAs Viviana Dovale-Farelo, William López-Pérez, Alvaro González-García, Rafael González-Hernández First principles calculations were performed to study the electronic and magnetic properties of cobalt (Co) doped aluminum arsenide (AlAs) within Density Functional Theory formalism. The study was done using a 6.25% Co concentration with a 2×2×2 supercell. |
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G60.00363: Strain effect on the electronic band structure of monolayer FeSe, a First Principle Study. Shuang Qiao The high Tc cuprates and iron-based superconductors have been the hotspot of people's research for a long time. More interestingly, a really high Tc has been reached in the monolayer FeSe with the STO substrate, which has the simplest structure in iron-based superconductors. Strain engineering is one of the most convenient method to modify the electronic structure and the Tc. Here, in the framework of First Principle calculations, we studied the band structure evolution of monolayer FeSe under strain effect. The in-plane compressive and tensile strain cause the shift of hole and electronic pocket while layer bend leads to the renormalization of the bands near Fermi level, which are both expected to influence Tc. |
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G60.00364: Engineering Graphene Work function by Changing Metal Adatoms and their Concentrations MERID Belayneh, Fadwa El-Mellouhi, Timothy Fisher, Sabre Kais, Fahhad Alharbi Graphene is one of the thinnest material to date, consisting of a single layer of carbon atoms arranged in aromatic rings forming a honeycomb-like structure. Doping graphene is of current research interests, aiming at improving and manipulating the electronic properties and work function of graphene through metal atom adsorption. In this work, we present a reduction of graphene work function by using different metal adatoms and their concentration. All the studied metal-doped graphene show a reduction of work function. However, the reduction varies for each metal and its concentration. In the case of Cs and Rb doped graphene, maximum work function reductions of 2.05 and 2.18 eV 1 respectively are obtained. Due to doping, the adatoms induce crucial changes in the electronic structure of graphene. The transfer of electrons from the adatoms to graphene shifts up the Fermi level. Consequently, normally semi-metallic graphene becomes metallic with a significant density of states at the Fermi level. In this work, we will present a detailed analysis of the electronic structure, absorption energy, and charge transfer for each adatom-graphene system. |
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G60.00365: Nano-scale displacement sensing based on van der Waals interaction. Lin Hu, Jin Zhao, Jinlong Yang We propose that a nano-scale displacement sensor with high resolution for weak-force systems can be realized based on vertically stacked 2D atomic corrugated layer materials through vdW interactions. Using first-principles calculations, we found that the electronic structure of bi-layer blue phosphorus (BLBP) vary appreciably with the lateral and vertical interlayer displacements. The variation of the electronic structure due to the lateral displacement is attributed to the change in the interlayer distance dz induced by atomic layer corrugation, which is in a uniform picture with vertical displacement. Despite the different stacking configurations of BLBP, we find the change of the band gap is proportional to dz-2. Further, this dz-2 dependence is found to be applicable to other graphene-like corrugated bi-layer materials. BLBP represents a large family of bi-layer 2D atomic corrugated materials for which the electronic structure is sensitive to the interlayer vertical and lateral displacement, and thus could be used for nano-scale displacement sensor. This can be done by monitoring the tunable electronic structure using absorption spectroscopy. |
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G60.00366: Quantum Back Action from Photo-Excited Electrons in Graphene Layers on Hybridization of Radiative and Evanescent Fields Danhong Huang, Andrii Iurov, Godfrey Gumbs, Alexei Maradudin We demonstrate the quantum back action from photo-excited Dirac electrons in two Coulomb-coupled graphene layers on the hybridization of radiative and evanescent field modes. The induced polarization fields in graphene layers significantly modify an incident surface-plasmon-polariton wave. This results in a high sensitivity to local dielectric environments and provides a unique tool for detecting and probing molecules selectively bound to carbons. Both optical-absorption spectra and scattering matrices of the surface-plasmon-polariton wave are calculated for frequencies close to the surface-plasmon resonance with various interaction strengths between two layers and the surface of a conducting substrate. |
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G60.00367: Polymorphism in two-dimensional tellurium crystals Hiroyuki Kumazoe, Aravind Krishnamoorthy, Lindsay Bassman, Fuyuki Shimojo, Rajiv Kalia, Aiichiro Nakano, Priya Vashishta Elemental layered materials have attracted much attention because they exhibit unique physical phenomena and a wide range of electronic properties ranging from metallic and semi-metallic to semiconducting. Recent experimental reports describe the vacuum-deposition-based synthesis and partial characterization of two-dimensional polymorphs of tellurium, dubbed tellurene. In this work, we perform quantum molecular dynamics (QMD) simulations to more thoroughly explore the atomic structure of tellurene. We identify several tellurene polymorphs that are consistent with experimental observations. Furthermore, we find several new tellurene polymorphs, which may be realized under tension. |
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G60.00368: Electronic and Optical Properties of Hydrogenated Surfaces of Transition Metal Chalcogenides Chiranjivi Lamsal, Santosh KC Using the first-principles calculation, hydrogenation of monolayers of transition metal dichalcogenides (TMDs) (MX2 with X = S, Se, Te and M =Mo, W) in their stable phases are investigated. The impact of hydrogenation of TMD surfaces on their structural, electronic and optical properties are studied. Hydrogenation of the surface is found to change their electronic and optical properties. Effect of hydrogen in the spin-orbit coupling is also studied. Hydrogen adsorption not only adds stability to the adsorbent but also tunes electronic, optical and magnetic properties, making the system useful for electronic device and sensor applications. |
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G60.00369: Quasiparticle Scattering Rates in The Extrinsic Germanene Po Hsin Shih, Yu-Huang Chiu, Thi Nga Do, Ming-Fa Lin The excited conduction electrons, conduction holes and valence holes in monolayer |
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G60.00370: Effects of Lead Halide Bridging of 2D Nanoplates on Excited State Relaxation Dynamics Mohammed Jabed, Svetlana Kilina PbSe Nanoplates (NPLs) – the 2-D nanostructures – are promising alternatives to quantum dots because it permits better controls on surface effects while holding all benefits of the electronic and optical properties resulted from the confinement. A Pb halide bridged self-assembled 2D PbSe NPL synthesized as reported by Koh et al1, show efficient carrier multiplication, enhance conductivity, and stimulated emission with a narrow width. These properties make NPLs promising materials for solar cell and lighting technologies. However, an impact of the interplay between 1D-confinement and Pb halide-originated defects, as well as effects of different halide molecule on relaxation dynamics are still unclear. We apply DFT based non-adiabatic dynamics combined with a simplified trajectory surface hopping (TSH) method to produce relaxation dynamics of charge carriers in Pb-halide bridged PbSe NPL. The electronic structure calculation shows that almost symmetric valance and conduction bands, while PbCl2 contributes to deeper valance band states, which could have effects on relaxation mechanisms of the hot carriers. Our calculation predicts about a twice faster relaxation of hot holes (< 1 ps), compared to the hot electron. |
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G60.00371: Novel unfolding method for multi subsystems each with distinct periodicity: examples of twisted-bilayer graphene and MoS2/graphene Yu-ichiro Matsushita, Hirofumi Nishi, Jun-Ichi Iwata, Taichi Kosugi, Atsushi Oshiyama We proposed a new unfolding scheme to analyze energy spectra of complex large-scale systems of each subsystem with distinct periodicity. To treat the super periodicity in materials coming from the stacks of different materials on the basis of the density-functional calculations, we usually use the supercell scheme. However, as a drawback of the supercell scheme, electronic bands are folded into the small supercell Brillouin zones (BZ) making it difficult to analyze the band structure and compare it with ARPES spectra. Band unfolding method is efficient for such cases. However, considering twisted bilayer graphene (tBLG) and MoS2/graphene as examples, we first show that the conventional unfolding scheme in the past using a single primitive-cell representation causes serious problems in analyses of the energy spectra. We then introduce our multi-space representation scheme in the unfolding method and clarify its validity for our target systems. |
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G60.00372: Polar Properties of PVDF Copolymers with Tetrafluoropropene: A First-Principles Based Study Ayana Ghosh, Lydie Louis, Alexandru Asandei, Serge Nakhmanson Polyvinylidene fluoride (PVDF, -CH2-CF2-) is a well-known organic electroactive compound — not only because of its respectable polar, piezoelectric and pyroelectric properties, but also as a convenient template for obtaining detailed insights into the nature of polymer ferroelectricity. In this investigation, we predictively evaluate the polar properties of β-PVDF copolymerized with 2,3,3,3-tetrafluoropropene (TFP, -CH2-CF(CF3)-) by utilizing a plane-wave-based density functional theory (DFT) approach. Contributions of individual VDF and TFP monomer dipole moments to the total polarization of the polymer crystal are identified from calculated maximally localized Wannier function (MLWF) charge centers. A number of different structural arrangements, involving combinations of β-PVDF chains with isotactic and syndiotactic TFP chains is explored, and the influence of these geometries on magnitudes of monomer dipole moments and total crystal polarization are elucidated. |
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G60.00373: A novel implementation to compute MP2 correlation energies without basis set superposition errors and complete basis set extrapolation Anant Dixit, Julien Claudot, Sebastien Lebegue, Dario Rocca By using a formulation based on the dynamical polarizability, we propose a novel implementation of second-order Møller-Plesset perturbation (MP2) theory within a plane wave (PW) basis set1. Because of the intrinsic properties of PWs, this method is not affected by basis set superposition errors. Additionally, results are converged without relying on complete basis set extrapolation techniques; this is achieved by using the eigenvectors of the static polarizability as an auxiliary basis set to compactly and accurately represent the response functions involved in the MP2 equations. Summations over the large number of virtual states are avoided by using a formalism inspired by density functional perturbation theory, and the Lanczos algorithm is used to include dynamical effects. To demonstrate this method, applications to three weakly interacting dimers are presented. |
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G60.00374: Magnetic, electronic and structural properties of: LiFePO4 : ab-initio study Miguel Sierra Cortes In this work we carry out the theoretical study of the structural, electronic and magnetic properties of Li(MnyFe1-y)PO4 for different concentrations of manganese (Mn). This compound is of great technological interest due to its use as a cathode in rechargeable lithium ion presenting properties such as low production cost, high degree of recyclability, and a stable structure under extreme conditions. The Study was performed with PWscf code, which allows first principle calculations within the formalism of Density Functional Theory using the generalized gradient approximation (GGA) and local density approximation (LDA+U). Structural properties such as lattice parameter, bulk modulus, volume were calculated for different concentrations of Mn in the compound. Forces between atoms were analyzed and adjusted according to Murnaghan approximation. Electronic properties such as density of states and band structure are also studied for GGA and LDA+U approaches. It was confirmed that GGA underestimates the band gap value while LDA+U gives a closer value to the experimental data. Finally, a linear relation between the total magnetic moment and Mn concentration was found for the compound. |
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G60.00375: Modeling Spin Fluctuations and Magnetic Excitations from Time-Dependent Density Functional Theory Tommaso Gorni, Iurii Timrov, Stefano Baroni Harnessing spin fluctuations and magnetic excitations in materials is key in many technologies, spanning from memory devices to information transfer and processing, to name but a few. A proper understanding of the interplay between collective and single-particle spin excitations is still lacking, and it is expected that ab initio simulations based on TDDFT will shed light on this interplay, as well as on the role of such important effects as spin-orbit coupling and related magnetic anisotropies. All the numerical approaches proposed so far to tackle this problem are based on the computationally demanding solution of the Sternheimer equations for the response orbitals or the even more demanding solution of coupled Dyson equations for the spin and charge susceptibilities. In the case of charge excitations, the Liouville-Lanczos approach to TDDFT has already been demonstrated to be a valuable alternative, the most striking of its features being the avoidance of sums over unoccupied single-particle states and the frequency-independence of the main numerical bottlenecks. In this talk we present an extension of this methodology to magnetic excitations and its implementation in Quantum ESPRESSO, as well as a few preliminary results on the magnon dispersions in bulk Fe and Ni. |
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G60.00376: Towards chemical accuracy: Fermi-Löwdin orbital self-interaction corrected density functional theory Torsten Hahn, Sebastian Schwalbe, Kai Trepte, Koblar Jackson, Jens Kortus In this contribution the authors give a brief insight into the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) method. FLO-SIC restores the correct 1/r behavior which will be shown based on various dissociation curves for diatomic molecules. Further, the binding energies are significantly improved compared to standard semilocal exchange-correlation functionals. In addition to the improved energetics, the Fermi-Löwdin orbitals allow a straightforward analysis of chemical bonding. |
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G60.00377: Fully Electromagnetic PIC/MCC Simulation for an Ion Thruster Discharge Chamber Shenglong Guo, Xiaolin Jin, Mingjuan Yang, Tongyu Liu, Xiaohui Ye, Bin Li Due to their high efficiency, high specific impulse, long lifetime and high reliability, ion thrusters have already become the research focus of the international electrical propulsion. In this work, a 2D axisymmetric Particle-in-Cell plus Monte Carlo Collision (PIC/MCC) numerical model was developed to simulate the plasma inside an ion thruster discharge chamber. The PIC method was used to describe the collective behavior of plasma, and detailed ionization collision mechanism between electrons and neutral gas was described by MCC method. Besides external electric and magnetic field, a fully electromagnetic model was solved to determine the effect of the electromagnetic fields in the particle tracking. Compared with previous electrostatic models, the effect of time-varying electromagnetic fields on charged particles was considered in a self-consistent way in this model. The numerical results such as single xenon ion, primary and secondary electron number density distributions, energy values obtained from this work are reasonable. New speed-up techniques including GPU parallel computing and multi-grid method will be used. |
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G60.00378: Comparative study on using force fields of three varying coarse-graining levels in the computational study of the behavior of DPPC lipid bilayer in the presence of DMSO. Hye-Young Kim, Deepesh Sigdel One of the main factors of a successful simulation is employment of a good set of force fields (ff) and the current understanding of the nature of coarse-graining in multiscale simulations is still limited. |
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G60.00379: Ground State Wave Function of Helium using Artificial Neural Network Gaurav Gyawali, Steven Rick Finding a wave function for any quantum mechanical system involves solving the famous Schrodinger equation which has analytical solutions for a few simple Hamiltonians. Solutions for more useful and complicated Hamiltonians are obtained by numerical methods which are greatly limited by computational resources. Recent advancement in the field of machine learning provides a very useful tool known as Artificial Neural Networks (ANN). The application of ANN to many-body quantum problems has recently been pointed out in the pioneering work by Carleo and Troyer. In this work, we solve the ground state wave function for Helium atom using the reinforcement learning method. Variational Monte Carlo (VMC) method in conjugation with Metropolis-Hastings algorithm will be used to numerically compute the expectation of various operators involved in the optimization of the trial wave function by using Stochastic Reconfiguration (SR). This work sheds light on the applicability of ANNs to quantum systems with spatial variable, rather than spin states as in the work of Carleo and Troyer. |
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G60.00380: Dynamical structure factor S(ω, k) of quantum Ising chain coupled to Bosonic dissipative bath Jian Wang Using the methods of Quantum Monte Carlo simulation + Numerical analytic continuation, |
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G60.00381: Study of Thermodynamics of Relativistic ion-electron Plasma Ecklin Crenshaw, Zephaniah Hernandez, Samina Masood We investigate the properties of a relativistic electron-ion plasma at extremely high temperature and density. We compute the plasma parameters such as Debye length, and Debye shielding as a function of temperature and density. We also studied the relativistic ions and electrons individually in a hot and dense medium under similar conditions. We witnessed how the plasma parameters change for the individually relativistic ion and electron plasmas in the presence of external energy. The properties of relativistic plasmas are compared with the regular low energy plasmas. |
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G60.00382: Plasma sheath model in the presence of field-induced electron emission. Jiba Dahal, Venkattraman Ayyaswamy Microplasma become the active area of research in the last decades because of its several applications in physics including nanomaterial synthesis, electronics, lighting, biomedicine, and metamaterials for controlling electromagnetic waves. More recently, field emission electrons from the field emission and their interaction with micro discharge due to high electric fields has shown to affect both pre and post breakdown. In this context, the current work focuses on the development of self-consistent sheath model. Microdischarges are driven by the field emission of electrons from the cathode which has been shown to play a role similar to secondary electron emission. This self-consistent sheath model using electric field and electron emission uniquely interplay between plasma and electrode to provide some insights into the current-voltage characteristics of microplasmas with an additional emission mechanism from the cathode. The results obtained from the model are evaluated and compare with PIC-MCC results. |
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G60.00383: Tilted Planar Interlinked Coils as a Means of Generating Rotational Transform – Modelling and Experiment Shah Faisal Mazhar, Francesco Volpe, Kenneth Hammond, Ruben Diaz-Pacheco, Ben Israeli, Jessica Li, Justin Mann, Jacob Austin, Veronica Mulila, Tommy Polanco, Albert Tai CIRCUS [1] is a toroidal device for the magnetic confinement of plasmas. It is constructively similar to a tokamak, but has no solenoid, nor other means to generate plasma current. Yet, it is predicted to generate the helical field necessary for confinement by simply tilting its 6 planar coils. In this last regard it is more similar to a torsatron or stellarator, except that its coils are simpler, planar, and, in fact, circular. Experiments are under preparation, in which an electron beam will be used to visualize the magnetic topology and compare it with calculations. This is made possible by an electron gun movable in three dimensions. An ongoing upgrade consists in epoxying the in-vessel coils for better vacuum. We will also present predictions for devices featuring more coils, resulting in more axisymmetric plasmas. |
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G60.00384: The Pythagorean Comma- Buckingham Π theorem perspective on the inter-relationship of the hydrogen quanta Donald Chakeres Purpose: Pythagoras utilized the Buckingham Π theorem to describe the physical interaction of two waves as a power law. This is related to a virtual frequency associated with the ratio of the power frequencies closest to 1, a frequency closest to 1 Hz, for the smallest powers. The quanta of hydrogen and their products/ ratios are inter-related by known power laws of 2, π, and the fine structure constant, and evaluated as harmonic power laws. The hypothesis is that the harmonic power laws of these quanta are related are highly ordered and equivalent to the Standard Model. |
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G60.00385: Design of the Code ‘BUMBLEBEE-EP’ and Its Application to Ion Thruster Xiaolin Jin, Tao Huang, Shenglong Guo, Mingjuan Yang, Tengyu Liu, Meiyu Liu, Xiaohui Ye, Quan Hu, Bin Li, Zhonghai Yang The PIC/MCC simulation code ‘Bumblebee-EP’ has been developed for the numerical research of ion thruster. It includes a friendly user-interface module that provides a powerful 3D solid-modeling front end, a 3D FEM meshes and graphical computational postprocessing and three physics simulators including the Discharge Simulator (DS), the Ion Optics Simulator (IOS) and the Plume Simulator (PS). Both DS and PS simulators used the 2D3V PIC/MCC method. The new 3D FEM-PIC algorithm was proposed to describe the physical process of ion extraction in grids and applied to IOS simulator. In this paper, the design of the code ‘Bumblebee-EP’ was introduced, the theory and numerical algorithms of the three physics simulators were described. The comparisons between MAGIC and Bumblebee-EP have been done to give the numerical validation. The characteristics of the ionization in discharge chamber, the ion extraction process with the CEX collision, and the formation of plume were simulated using Bumblebee-EP. |
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G60.00386: The Hybrid Simulation MPM Model for ECR Ion Source Li Lei, Xiaolin Jin, Tao Huang, Bin Li, Zhonghai Yang A new hybrid simulation model named MAGY/PIC/MCC (MPM) has been developed for ECR ion source. We chose the MAGY theoretical model to describe the time-varying electromagnetic fields, the PIC method to deal with the interaction between the charged particles and fields, and the MCC method to simulate the collisions among particles. The generalized telegrapher's equations in MAGY are built by means of expanding perfect waveguide modes. Thus the electromagnetic fields can be considered as a superposition of different modes and frequencies and calculated respectively. We chose the PIC/MCC scheme to deal with the dynamics of particles which can describe both the collective and collision motions. Furthermore, in order to build a self-consistent description of the interactions between the charged particles and the electromagnetic wave, we present the new current source terms associated with MAGY and by far we have completed the verification of their effectiveness. Theoretically, compared with the existing algorithms, the MPM model has better computational accuracy and efficiency, and meanwhile keeps the abundant numerical diagnosis. |
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G60.00387: METALS AND METALLIC ALLOYS
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G60.00388: Ab initio Calculations of Structure and Elastic Properties of Lightweight High-Entropy Alloys (HEAs). Natalia Koval, Iñaki Juaristi, Ricardo Díez Muiño, Maite Alducin High Entropy Alloys (HEAs) are a new class of metallic alloys with 5 or more principal elements, with the concentration of 5% to 35% each one. Despite the complex composition, HEAs are believed to form simple crystal structures, depending on the valence electron concentration VEC (BCC if VEC<6.8, FCC if VEC>8, mixed phases in between). Due to their unusual design, these alloys often exhibit special properties. The combination of such properties as low density, high strength, and corrosion resistance makes possible many potential applications of HEAs in aviation, engineering, orthopedics (bone implants), etc. The aim of our work is to study the atomic structure as well as the electronic and elastic properties of lightweight HEAs using density functional theory and evolutionary crystallography methods. The methodology is tested by calculating and comparing the elastic properties with the existing data for certain alloys. |
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G60.00389: Experimental Characterization of Crackling Noise in Microplastic Regime of Bulk Metallic Materials Xiaoyue Ni, Gabriele Vajente, Eric Quintero, Koji Arai, Eric Gustafson, Norna Robertson, Julia Greer, Rana Adhikari During plastic flow, metallic materials deform through collective dislocation activities, and exhibits mechanical fluctuation, i.e. crackling noise. Micro-plastic deformation, associated with smaller dislocation activities prior to nominal yielding, has been detected in sub-micron-scale single crystals. Such mechanical noises, arising in metallic materials subjected to nominal elastic stress excitations, can be a relevant problem for instrumentation that requires high strain sensitivity, e.g., gravitational wave detectors like Advanced LIGO. In this study, we endeavor to detect and characterize the mechanical up-converted crackling noise in macroscopic samples. An instrument has been custom-built based on a Michelson interferometer. It has achieved an ultra-high displacement noise resolution of 1e-14 m/sqrt(Hz) in the frequency range of 10~1000 Hz. We resolved a stress-modulated noise in a pair of cm-scale maraging steel spring cantilevers under nominal elastic loading. The characteristics of the noise resemble those of the micro-plastic noise predicted from micro-mechanical simulations developed based on the microscopic experiments. |
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G60.00390: Experimental Search for Avalanches of Entangled Dislocations as a Source of Dissipation and Mechanical Noise Morgan Shaner, Marina Mondin, Riccardo DeSalvo, Samavarti Gallardo, Nicole Araya, Greta O'Dea, Hope Hamamoto Recent measurements using highly sensitive instruments have shown increased dissipation and the appearance of random low frequency noise in metal flexures. These effects have been attributed to avalanches of dislocations, a phenomenon supposedly controlled by self-organized criticality (SOC) statistics. This experiment is attempting to detect these subtle effects using a variation on the rotating beam Kimball-Lovell 1927 experiment that was used to measure the loss angle of materials above 1Hz. We have demonstrated the feasibility of making measurements of loss angle with μ-radian precision at arbitrarily low frequencies. If dislocation avalanches are the source of the 1/f noise in these flexures, we expect to see them using this experiment. |
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G60.00391: Effective Hamiltonian approach to optical chirality and optical activity induced by Weyl spin-orbit interaction Hideo Kawaguchi, Gen Tatara Rashba spin-orbit interaction leads to electromagnetic cross-correlation effects such as Edelstein and inverse Edelstein effects, |
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G60.00392: First-principles study of anomalous thermoelectric effect in CoMSb(M=Sc, Ti, V, Cr, Mn) Susumu Minami, Fumiyuki Ishii, Yo Mizuta, Mineo Saito The half-Heusler alloys, intermetallics with face-centered cubic crystal structure and chemical composition of XYZ, exhibit many peculiar properties, such as half- metallic ferromagnetic state and large thermoelectric effect. It is well known that the half-Heusler alloys are good thermoelectrics exhibiting large Seebeck effect originating from its narrow gap semiconducting state with 18 valence electron counts per formula unit. Recently, the anomalous Nernst effect (ANE) has attracted attention as a new thermoelectric generation mechanism and the large ANE was reported experimentally in the Heusler alloy Mn3Sn [1]. In this work, we focused on carrier-dependence of thermoelectric properties including ANE in half-Heusler alloys. We have performed first-principles computations on half-Heusler alloys CoMSb (M=Sc, Ti, V, Cr, Mn) and found that the crystal-momentum component of effective magnetic field generates large ANE when the chemical potential is properly tuned. This behavior was clearly understood by the energy-dependent anomalous Hall conductivity. [1] M. Ikhlas, T. Tomita, T. Koretsune, M. Suzuki, N. Daisuke, R. Arita, Y. Otani, and S. Nakatsuji, Nat. Phys (2017). |
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G60.00393: Magneto-electric and thermo-electric transport properties in bulk Ge2Sb2Te5 Ming Yin, Lei Wang, Lurinea Powell, Godwin Mbamalu, Michael Wescott, Timir Datta We report on electrical conductivity (C) and Seebeck coefficient (S) in bulk Ge2Sb2Te5, a phase change material (PCM) from room temperature down to ~500 mK under a range of applied magnetic fields (B< 20 T). The zero field resistivity data is adequately described by the Block- Gruneisen formula. In addition zero field (B=0) C and S is observed to follow a generalized Noritheim-Gorter like scaling behavior. Which may indicate that two independent types of scattering processes is dominant in controlling the transport rate in this material. A positive magnetoresistance, i.e., DC resistance is increased when a magnetic field is applied. However, the field dependence is neither quadratic nor linear in B. Instead the observed rate is sublinear in B, in other words DR(B)/R(0) is a concave function of B. |
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G60.00394: Simple Diffusion Hopping Model with Convection Barry Fitzgerald, Johan Padding, Rutger Santen The transportation of matter in particulate systems has been the subject of significant computational study using a variety of approaches such as particle hopping models. While hopping models fully describe particle diffusion, these models do not capture convective particle motion. |
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G60.00395: The effects of physical aging in a polyetheramine-cured DGEBA epoxy Kelsey Wilson, Jamie Kropka, John McCoy As amorphous polymers are cooled, a temperature (Tg) is reached where molecular rearrangements are no longer possible on the time scale of the temperature change. Below Tg, only gradual structural rearrangements (physical aging) are possible as the polymer tries to approach its thermodynamic equilibrium. Samples of a polyetheramine (Jeffamine T-403)-cured digylcidyl ether of bisphenol A (DGEBA) resin (EPON 828) were aged isothermally to examine the effects of physical aging on the mechanical and calorimetric responses. Physical aging was probed through uniaxial compression tests to observe changes in the stress-strain response, and differential scanning calorimetry to observe the evolution of the endothermic peak in the heat capacity. The compressive yield stress substantially increased with aging time, as did the magnitude of the peak in heat capacity and the temperature at which the peak occurred. It is important to understand the implications of these changes on the lifetime of engineering devices that utilize the 828/T-403 material. |
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G60.00396: Top-gated n-type Carbon Nanotube Field Effect Transistors using SiNx dielectric for Logic Circuit Applications P R Yasasvi Gangavarapu, Anjanashree M R, A K Naik Semiconducting single walled carbon nanotubes (CNTs) are considered to be one of the best alternates to Silicon particularly beyond 10 nm node transistor technology. There have been reports demonstrating CNTFET complementary (using both p- and n-FETs) circuits. Most of the reports on CNT based complementary circuits involved fabrication of n-type CNTFETs using rare earth metals for source/drain contacts. This approach may not be suitable for large scale manufacturing. In this work we have fabricated top-gated n-type solution-processed CNTFETs using Silicon Nitride (SiNx) as gate dielectric and evaluated their performance for logic circuit applications. The n-CNTFETs are contacted (source/drain) using regular metals such as Palladium. SiNx thin film is deposited over CNTs using low temperature Plasma Enhanced Chemical Vapor Deposition (PECVD) to realize air-stable n-CNTFETs. The SiNx film serves both as passivation layer and gate dielectric. We have studied the effect of SiNx film thickness on the performance of n-CNTFETs. Using the top-gated n-CNTFETs (with an Effective Oxide Thickness of ~10 nm), we have demonstrated a logic inverter circuit. This approach to fabricate top-gated n-CNTFET logic circuits is CMOS compatible and is suitable for large scale manufacturing. |
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G60.00397: Modeling Business Cluster Life Cycles Using Non-Equilibrium Statistical Physics Margaret Kallus, Rebecca Melkerson, Rossella Gabriele, Irina Mazilu, Dan Mazilu The economics literature has substantial empirical documentation on the impact of agglomerative forces in business cluster formation. We introduce a cooperative sequential adsorption model to describe business cluster formation over time based on the spatial concentration of firms from the same industry. This model simulates the growth and decay of a cluster over time on an NxN square lattice under the condition of finite resources. Growth and decay rates are probabilistic functions of the number of sites already containing businesses. Once the resources are exhausted, our clusters either experience a period of temporary renewal consistent with economic theory or undergo a period of decline. |
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G60.00398: Superconducting (Li, Fe)OHFeSe Film of High Quality and High Critical Parameters Yu Huang, ZhongPei Feng, Shunli Ni, Jun Li, Wei Hu, Shaobo Liu, Yiyuan Mao, Huaxue Zhou, Zhou Fang, Kui Jin, Huabing Wang, Jie Yuan, Xiaoli Dong, Zhongxian Zhao A superconducting film of (Li1-xFex)OHFeSe is reported for the first time. The thin film exhibits a small in-plane crystal mosaic of 0.22o, in terms of the full width at half maximum of X-ray rocking curve, and an excellent out-of-plane orientation by X-ray φ-scan. Its bulk superconducting transition temperature Tc of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field Hc2 is estimated to be 79.5 T and 443 T for the magnetic field perpendicular and parallel to the ab plane, respectively. Moreover, a large critical current density Jc of a value over 0.5 MA/cm2 is achieved at ~20 K. Such a (Li1-xFex)OHFeSe film is therefore not only important to the fundamental research for understanding the high-Tc mechanism, but also promising in the field of high-Tc superconductivity application, especially for high-performance electronic devices and large scientific facilities such as superconducting accelerators. |
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G60.00399: Magnetic Characteristics of Erbium Based Orthoferrites Lorena Aguirre, Stephen Tsui The rare-earth orthoferrites are well known for demonstrating a spin reorientation phenomenon. We investigate the effects of Cr doping in the Fe sites in Erbium- based orthoferrite, ErFeO3. Polycrystalline ErFe1-xCrxO3 samples were prepared by conventional solid state reaction method and their magnetic properties studies via vibrating sample magnetometry in the temperature range 50 K-300 K. |
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