Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session K1: Poster Session II (2:00pm - 5:00pm)
Sponsoring Units: APSRoom: Hall D
|
K1.00001: QUANTUM FLUIDS AND SOLIDS |
|
K1.00002: Riemann-Hypothesis Millennium-Problem(MP) Physics Proof via CATEGORY-SEMANTICS(C-S)/F=C Aristotle SQUARE-of-OPPOSITION(SoO) DEduction-LOGIC DichotomY J. Baez, M. Lapidaryus, Edward Carl-Ludwig Siegel Riemann-hypothesis physics-proof combines: Siegel-Antonoff-Smith[AMS Joint Mtg.(2002)-Abs.973-03-126] digits on-average statistics HIll[Am. J. Math 123, 3, 887(1996)] logarithm-function's (1,0)-fixed-point base=units=scale-invariance proven Newcomb[Am. J. Math. 4, 39(1881)]-Weyl[Goett. Nachr.(1914); Math. Ann. 7, 313(1916)]-Benford[Proc. Am. Phil. Soc. 78, 4, 51(1938)]-law [Kac, Math. of Stat.-Reasoning(1955); Raimi, Sci. Am. 221, 109(1969)] algebraic-inversion to ONLY Bose-Einstein quantum-statistics(BEQS) with digit d = 0 gapFUL Bose-Einstein Condensation(BEC) insight that digits are quanta are bosons were always digits, via Siegel-Baez category-semantics tabular list-format matrix truth-table analytics in Plato-Aristotle classic "square-of-opposition" : FUZZYICS=CATEGORYICS/Category-Semantics, with Goodkind Bose-Einstein condensation(BEC) ABOVE ground-state with/and Rayleigh(cut-limit of "short-cut method";1870)-Polya(1922)-"Anderson"(1958) localization [Doyle and Snell, Random-Walks and Electrical-Networks, MAA(1981)-p.99-100!!!]. [Preview Abstract] |
|
K1.00003: Drag effects in a system of electrons and microcavity polaritons Oleg Berman, Roman Kezrashvili, Yurii Lozovik The theory of the drag effects in the system of spatially separated electrons and excitons in coupled quantum wells (QWs) embedded in an optical microcavity is developed. It is shown that for systems of spatially separated interacting quasiparticles is the possibility of controlling the motion of the quasiparticles of one subsystem by altering the parameters of state of the quasiparticles in the other subsystem, for example, controlling the flow of polaritons or exciton using a current of electrons. At low temperatures, the electron current dragged by the polariton flow is strongly suppressed and hence, the absence of the electron current indicates the superfluidity of polaritons. However, the polariton flow can be dragged by the electrons, and, therefore, there is a transport of photons along the microcavity, which decreases with rise of the superfluid component and can be observed through the change in angular distribution of photons discussed above. At high temperatures, from one hand, the existence of the electric current in the electron QW indicates the exciton flow in the other QW, and from the other hand, the electron current in one QW induces the exciton flow in the other QW via the drag of excitons by the electrons. The drag coefficients for the polariton-electron systems are calculated and analyzed. [Preview Abstract] |
|
K1.00004: UNDERGRADUATE RESEARCH / SOCIETY OF PHYSICS STUDENTS |
|
K1.00005: Celebrating Five Years of SPS: A lesson in building physics outreach from scratch Jerome T. Mlack, Roberto Ramos It has been almost five years since SPS was revived at Drexel University. Until 2006 Drexel SPS had been inactive for two decades. In this poster we report the challenges of building a chapter from scratch and turning it into an active and award-winning group. The students are constantly involved in mentorship programs in the underserved Philadelphia school district, while regularly seeking opportunities to perform and present research. We report the various activities we have initiated, and the lessons we have learned from them. [Preview Abstract] |
|
K1.00006: Exploring the Depletion Layer: An Investigation into How Water Reacts when Confined to a Hydrophobic Surface Isaac Marx, Adele Poynor We observe water interacting with surfaces everyday. It forms spherical drops on hydrophobic surfaces, such as a freshly waxed car, and it spreads out on hydrophilic surfaces. However, water acts much differently when it is confined to a hydrophobic area. In our experiment, Surface Plasmon Resonance (SPR) is utilized to find differences in surface conditions. Tests are done for the interface of a hydrophobic surface surrounded by water and also for a hydrophobic surface surrounded by methanol, which we know will not form a depletion layer. With this data we are able to analyze the optical properties of the depletion layer in much greater detail. [Preview Abstract] |
|
K1.00007: Exploring Isothermal Layers in the Stable Atmospheric Boundary Layer Joseph Wilkins Simulating the stable atmospheric boundary-layer presents a significant challenge to numerical models due to the interactions of several processes with widely varying scales. The goal of this project is to more clearly define the cause of isothermal layers observed during the Meteorological Experiment in Arizona's Meteor Crater and to test the National Taiwan University/Purdue University (NTU/P) model in stable environments with complex terrain. The NTU/P model is able to utilize the actual terrain data with minimal smoothing for stability. We have found that isothermal profiles can be generated by the standing wave that develops due to weak wind flowing over the crater. However, the horizontal heterogeneity is greater than observed. Continued effort will explore enhancing horizontal mixing due to turbulence and radiative transfer. [Preview Abstract] |
|
K1.00008: Drug Loading of Mesoporous Silicon Anne Moffitt, Jeff Coffer, Mengjia Wang The nanostructuring of crystalline solids with low aqueous solubilities by their incorporation into mesoporous host materials is one route to improve the bioavailability of such solids. Earlier studies suggest that mesoporous Si (PSi), with pore widths in the range of 5-50 nm, is a candidate for such an approach. In this presentation, we describe efforts to load curcumin into free-standing microparticles of PSi. Curcumin is a compound extracted from turmeric root, which is an ingredient of curry. Curucmin has shown activity against selected cancer cell lines, bacteria, and other medical conditions. However, curcumin has a very low bioavailability due to its extremely low water solubility (0.6$\mu $g/mL). Incorporation of curcumin was achieved by straightforward loading of the molten solid at 185$^{\circ}$C. Loading experiments were performed using PSi particles of two different size ranges, 45-75 $\mu $m and 150-250 $\mu $m. Longer loading times and ratio of curcumin to PSi leads to a higher percentage of loaded curcumin in both PSi particle sizes (as determined by weight difference). The extent of curcumin crystallinity was assessed by x-ray diffraction (XRD). The solubility and release kinetics of loaded curcumin from the PSi was determined by extraction into water at 37$^{\circ}$C, with analysis using UV-VIS spectrometry. [Preview Abstract] |
|
K1.00009: Identification of gram-negative and gram-positive bacteria by fluorescence studies Jonathan Demchak, Joseph Calabrese, Marian Tzolov Several type strains of bacteria including Vibrio fischeri, Azotobacter vinelandii, Enterobacter cloacae, and Corynebacterium xerosis, were cultured in the laboratory following standard diagnostic protocol based on their individual metabolic strategies. The bacterial cultures were not further treated and they were studied in their pristine state (pure culture - axenic). The fluorescent studies were applied using a continuous wave and a pulsed excitation light sources. Emission and excitation spectra were recorded for the continuous wave excitation and they all show similar spectral features with the exception of the gram positive bacteria showing vibronic structures. The vibrational modes involved in these vibronic bands have energy typical for carbon-carbon vibrations. The fluorescence is quenched in addition of water, even a very thin layer, which confirms that the observed spectral features originate from the outer parts of the bacteria. These results allow to conclude that the fluorescence spectroscopy can be used as a method for studying the membranes of the bacteria and eventually to discriminate between gram positive and gram negative bacteria. The pulsed experiments show that the fluorescence lifetime is in the sub-microsecond range. The results indicate that the observed spectra are superposition of the emission with different lifetimes. [Preview Abstract] |
|
K1.00010: Electrocardiogram analysis through time discrete Fourier transform Cameron Lancaster, Guoping Zhang The motivation for this research is to find an alternative method to diagnose heart conditions. This can be accomplished by analyzing wave patterns in EKG data, and using the Fourier Transform to compare steady wave patterns against fibrillating wave patterns. The two main contributors are the following: heart electricity and Fourier Transform. Also, it is recognized that ion movement has potential to change the frequency in any heart beat signal. This effect is caused due to a strong electrostatic attraction that causes the membrane capacitance to build charge. For a single ion focus, the Nernst Potential influences the equilibrium potential for the membrane of an ion. If two or more ions are contributing to an electric field charge, the Goldman-Hodgkin-Katz will find the membrane equilibrium potential. If a membrane has an efflux, or influx, of ions, then it is possible to get the passive flow of the electric current to zero. In continued research, we will gain knowledge of solving equations; such as ionic flux, quantitative diffusion, electric current density, and more. The finishing portion of this research will be to compare the Fourier Transformed wave graphs to determine heart conditions. [Preview Abstract] |
|
K1.00011: In-Vivo Proton Therapy Dosimetry Using Scintillating Fiber Technology Ashley Cetnar, Paul Gueye Proton therapy is a cancer treatment modality that uses high-energy proton beams to irradiate cancerous cells while minimizing the radiation to healthy tissue. Because of its Bragg peak distribution, a proton is more efficient in localizing doses than conventional x-ray therapy. When the protons interact within the body, there are many reactions that induce secondary radiation. To date, there is still no accurate device available that is capable of measuring the beam profile and effective dose delivery during the treatment. This research focused on the use scintillating fibers technology to measure the secondary emitted radiation exiting a water phantom tank and the delivery system bombarded by proton beams. A realistic Geant4 Monte Carlo simulation was also developed to provide additional information to further optimize our prototype. This poster presents the results obtained from preliminary experimental and simulated studies for a possible real time radiation detection system using scintillating fibers. [Preview Abstract] |
|
K1.00012: Approximating the Production Rate for Neutrino-Induced Pair-Production in Intense Magnetic Fields Jordan Russell We consider the production of electron-positron pairs by neutrinos in an intense magnetic field. Calculating the total production rate of these pairs requires summing over all of the allowed Landau levels of the electron and positron for a range of incoming neutrino energies. Because of the computationally challenging nature of this summation, the focus of my research has been to institute a set of estimations and calculate the total rate over the dominant region of Landau-level space. I will present an approximate relationship for field strengths in excess of the critical field. [Preview Abstract] |
|
K1.00013: The Optimization and Implementation of the Qweak Database Udai Garimella, Damon Spayde The Qweak experiment at Thomas Jefferson National Accelerator Facility (J-Lab) is an attempt to precisely measure the parity violation observed in low energy electron-proton scattering events. Specifically, the weak charge of the proton will be measured to $4\%$ error, which will, in turn, be used to calculate the ``running'' Weinberg mixing angle $(\sin^{2}(\theta_w))$. Since the Standard Model makes a firm prediction for $(\sin^{2}(\theta_w))$ at low energies, the experiment presents an opportunity to test the limits of this model. Any significant variation in$(\sin^{2}(\theta_w))$ from the expected value would be indicative of new physics, while an agreement would place strict constraints upon the existing model. In order to make an exact measurement of the weak charge, large amounts of data (almost 2200 hours worth) will be gathered. A large, robust database is needed to store and organize this data, so it can be analyzed in an easy and effective manner. The optimization and implementation of this database will be discussed. [Preview Abstract] |
|
K1.00014: Optimizing the Josephson Parametric Amplifier - A numerical study Zlatko Minev, Rajamani Vijayaraghavan, Irfan Siddiqi Recent progress in quantum information processing using superconducting circuits has stimulated interest in low noise amplifiers which operate at the quantum limit. Josephson parametric amplifiers (paramp) based on low quality factor (Q) non-linear resonators are a promising candidate for quantum state readout. We present a numerical study to optimize the paramp for dynamic range and bandwidth by investigating the lowest resonator Q compatible with high gain and low noise performance in the 4-- 8 GHz range. We also investigate designs involving multiple junctions and weak-link junctions to further optimize the dynamic range. Such an amplifier can be used for single shot readout of superconducting qubits and real time detection of the quantum state---crucial developments for implementing quantum feedback and error correction. [Preview Abstract] |
|
K1.00015: Image processing of transmission ion microscopy webcam video with Iris software Nicole Newton, Arthur Pallone Scientists and engineers build simple, low-cost, webcam-based instruments for use in many disciplines. Analysis of the optical signal received through the three broadband color filters -- red, green and blue -- form the basis of many of those instruments. The CMOS sensors in webcam pixels also produce signals in response to ionizing radiations -- such as alpha particles from a radioactive source. Simple alpha radiography has been demonstrated with a commercially available antistatic Po-210 source and a webcam modified to expose the pixel sensors. Analysis of webcam video with the Iris software is presented as a way to demonstrate other transmission ion microscopy imaging modes. [Preview Abstract] |
|
K1.00016: Cathodes with modified morphology for polymer light emitting devices Jacob Cox, Marian Tzolov This work is the result of a junior year research project on fabrication and characterization of Polymer Light Emitting Devices (PLEDs). The PLEDs were created on top of indium tin oxide coated glass substrates, starting with a 60 nm thick hole injection layer, followed by an 80 nm layer of PPV-MEH polymer. The structures were finalized by a thermally evaporated aluminum film acting as the cathode for the device. We have concentrated on modifying the structure and morphology of the aluminum cathode in conjunction with the variation of the polymer film thickness. The devices were tested using current- voltage and light-voltage characteristics, light emission spectroscopy, device lifetime testing, profilometry, and optical microscopy of device degradation. The structure of the aluminum films was evaluated by SEM imaging. The results from this complex study showed a correlation between the morphology of the metal electrodes with the performance of the PLEDs. [Preview Abstract] |
|
K1.00017: Spatio-temporal beam profiling of pulsed infrared laser sources Ian Reeves, Jeffrey Olafsen, Linda Olafsen Development of viable infrared lasers relies not only on the power and wavelength generated by the source, but also on the spatial and temporal profile of the output beam. Thermal imaging is of particular interest to researchers working in the field of optically pumped semiconductor analysis as the output from many of these devices falls in the mid-infrared range. While knife edge and other beam profile analysis techniques typically are unable to capture the temporal evolution of beam profiles, real time imaging is employed in this work, using a thermal camera synchronized with a Nd:YAG pump laser via LabVIEW-controlled triggering. Coupling the synchronization with detailed image analysis using IDL, this new methodology is applied to the near-infrared output of an optical parametric oscillator and ultimately will be extended to mid-infrared semiconductor lasers. [Preview Abstract] |
|
K1.00018: Development of a Portable Automated Gas Environment System (PAGES2) Nathan Campbell, Jacob Baxley, Edward Kintzel, Bruce Hill, Louis Santodonato, Kenneth Herwig For the user community at the Spallation Neutron Source (SNS), a portable automated gas environment system (PAGES2), capable of remote operation at pressures up to 100 bar has been built and programmed. The function of this system will be to characterize a variety of high surface area materials and allow studies of energy significant gases such as methane on these surfaces to be carried out. Understanding the fundamental physics of interaction at the gas-surface interface is key for the generation of application-minded products such as fuel cells. PAGES2 can generate adsorption isotherms to determine surface area of the material as well as the number of gas molecules required for a specific surface coverage. This system will not only produce new science, but also allow for better experimental design. PAGES2 system testing is currently underway, and initial results indicate the system is operating as designed. Future tests will be done prior to use at the SNS. [Preview Abstract] |
|
K1.00019: Realization of a closed-cycle dilution refrigerator for nanoscale magnetometry Ravi Naik, Anirudh Narla, Yu-Dong Sun, Natania Antler, Irfan Siddiqi We present the implementation of a mechanical pump-free, dilution refrigerator with an automatic cool-down protocol. The cooling process utilizes a liquid nitrogen pre-cool circuit, a pulse tube cooler, and a custom internal dilution unit manufactured by Chase Cryogenics. The dilution unit employs charcoal sorption pumps and electronic heat switches to regulate the condensation and subsequent evaporative cooling of $^{3}$He, $^{4}$He, and a mash of both in three separate chambers. We achieve a base temperature of 85 mK with a 10-15 hour hold time. The unit presents a simple, compact, low vibration platform for conducting a wide spectrum of low temperature transport experiments. As an example, we present microwave frequency SQUID magnetometry data collected in this unit. [Preview Abstract] |
|
K1.00020: Phase cycling for optical two-dimensional Fourier-transform spectroscopy Travis Autry, Galan Moody, Hebin Li, Mark Siemens, Steven Cundiff Phase-cycling has been implemented in optical two-dimensional Fourier-transform spectroscopy to extract signals from quantum wells and quantum dots and to eliminate noise such as pump scatter co-propagating with the four-wave mixing signal. Experiments using actively phase-stabilized interferometers to cycle the excitation pulse optical phases suffer from partial noise cancellation because excitation and phase-control laser wavelengths are incommensurate. To obtain full noise elimination, we have incorporated liquid crystal variable retarders capable of imposing a $\pi $ phase shift for wavelengths 650-950 nm. We present non-rephasing spectra of potassium vapor contained in a $\sim $20 $\mu $m transmission cell and show that this phase cycling method removes all noise from pump scatter while drastically reducing the data acquisition time compared to mechanical phase-delay techniques. [Preview Abstract] |
|
K1.00021: ABSTRACT WITHDRAWN |
|
K1.00022: Designing an Optical Dipole Trap for the Creation of Bose-Einstein Condensates Amy Van Newkirk, L.S. Leslie, A. Hansen, N.P. Bigelow Bose-Einstein condensates have been produced with many different configurations of magnetic, optical, and hybrid traps. Pure optical dipole traps have the possibility of providing a spin state independent trapping potential, which is necessary in many BEC experiments. We are currently designing a red-detuned, single focused-beam dipole trap to be used in the production of BECs. The BEC is to be formed from rubidium-87 atoms. The lab currently has a magneto-optical trap and an Ioffe-Pritchard magnetic trap in place. The dipole trap will be the last step in the process to create a BEC. It will be formed with a single pass of a Yb fiber laser at 1064 nm. We developed a model for the dipole trap potential in mathematica. Using this model, we were able to see that our current lab configuration has the possibility of producing a dipole trap that will allow for Bose-Einstein condensation. [Preview Abstract] |
|
K1.00023: SEM and EDX Study of Al alloy Precipitant Surface Segregation due to Annealing Austin Mohney, Indrajith Senevirathne In Al alloys, precipitation hardening by impurity phase metallic microstructures in the main bulk metal is a norm. This results in resilience against dislocations, and improvement in other favorable attributes. We have studied Al 2024, Al 5052, Al 6061, and Al 7075 systems and their constituent precipitant migration due to thermal annealing. Scanning Electron Microscopy (SEM) was used to study the structure/morphology. Electron Dispersive X ray Spectroscopy (EDX) was used to study the near surface elemental variations. At annealing these alloys systems exhibit temperature activated relative segregation of the precipitants. Considering main constituents, it was observed Cu precipitant in 2024, and Mg precipitant in 6061 segregated to the surface. Further, increment in the ambient C absorption and O desorption on the surface layers were observed. Surface morphology variations were also studied at annealing using SEM. The data obtained will be discussed in terms of standard diffusion models for the alloys and corresponding diffusion coefficients. [Preview Abstract] |
|
K1.00024: AFM and EDX Study of Self Assembled Pt Nanostructures on PEDOT Thin Films under Ambient Conditions Indrajith Senevirathne, Austin Mohney, Joshua Buchheit, Anura Goonewardene Noble metal nanostructure systems on conductive polymer thin films under ambient conditions are interesting due to their use in BioMEMS and hybrid systems further and considering the physics of the polymer - metal interactions The observed nanostructures have deformed spherical shape. The Pt was magnetron sputter deposited at RT (300K), PEDOT Baytron P 60nm thick, spin coated on glass slides cleaned with acetone and IPA. The system was studied using ambient IC mode Atomic Force Microscopy (AFM) for its structure. Elemental composition/distribution of the system was measured with Energy Dispersive X ray Spectroscopy (EDX). Pt nanostructures on the surface observed to be likely Volmer - Weber growth mode At Pt coverage of 120 ML, nanostructures had a mean diameter of 32 nm and mean height of 5 nm. When annealing at 15min at 473K systems changes to smaller nanostructures coexisting with bigger structures of mean diameter of 120 nm and mean height of 36 nm. Elemental/morphological variations when annealed at successively higher temperatures were also investigated. [Preview Abstract] |
|
K1.00025: AFM, and EDX Study of Self Assembled Au Nanostructures on P doped Si(100) Under Ambient Conditions Joshua Tatham, Joshua Buchheit, Indrajith Senevirathne Noble metal nanostructures systems on semiconductor surface under ambient conditions are interesting but complex due to the presence of surface adsorbed species. Apart from various possible plasmonic and catalytic applications and these may give insights into thermodynamics and kinetics of such systems. The observed nanostructures have deformed spherical shape. The Au was magnetron sputter deposited at RT (300K), on Si(100) P doped cleaned with acetone and IPA. Ambient IC mode Atomic Force Microscopy (AFM) used to elucidate structure. Elemental composition and distribution on the deposited system was measured with Energy Dispersive X ray Spectroscopy (EDX). Self assembled Au nanostructures on the surface was observed with likely Stranski - Krastanov growth mode At 30 ML Au coverage of nucleated nanostructures observed to have a mean diameter of 2 nm and mean height of 2 nm. At Au coverage of 120 ML, nanostructures had a mean diameter of 25 nm and mean height of 4 nm. Observed variations when annealed at successively higher temperatures will also be discussed [Preview Abstract] |
|
K1.00026: Pt Nanostructures Self Assembled on P doped Si(100) Under Ambient Conditions: AFM, and EDX Study Zachary Barcikowski, Austin Mohney, Indrajith Senevirathne Noble metal nanostructures on surface support under ambient conditions are interesting but complex due to the presence of surface adsorbed species. System may have plasmonic and catalytic uses from the applications standpoint and may give insights into thermodynamics/kinetics of such systems. Observed Pt nanostructures have deformed spherical shape. The Pt was magnetron sputter deposited at RT (300K), on Si(100) P doped cleaned with acetone and IPA. The system was studied using ambient IC mode Atomic Force Microscopy (AFM) for its structure. Elemental composition / distribution were measured with Energy Dispersive X ray Spectroscopy (EDX). Self assembled Pt nanostructures on the surface was observed with a likely Stranski - Krastanov type growth mode At Pt 30 ML coverage nucleated nanostructures observed to have a mean diameter of 15 nm and mean height of 1.5 nm. At Pt coverage of 120 ML, structures exhibited mean diameter of 40 nm and mean height of 3 nm. System was also observed at incremental annealing as well [Preview Abstract] |
|
K1.00027: Thermal conductivity of a two-gap superconductor MgB$_{2 }$in High Magnetic Field and Low Temperatures Michael Garman, Sasha Dukan We calculate the thermal conductivity for a single MgB$_{2}$ crystal in a mixed state, placed in high magnetic field at zero temperature. We plot the thermal conductivity in the superconducting state $\kappa $(H) rescaled by the normal state value $\kappa _{N}$ as a function of magnetic field for a realistic $i.e.$ disordered MgB$_{2}$ superconductor. Our theoretical curve exhibits good qualitative agreement with the experimental data. We report on the self-consistent calculation of the influence disorder has on the thermal conductivity. [Preview Abstract] |
|
K1.00028: Low Temperature Study of the Electrical Properties of Sb-SnO$_{2}$ Nanofibers Maritza Reyna, Idalia Ramos, Nicholas Pinto Antimony-doped tin oxide (ATO) can be used for many applications including the development of gas sensors, energy storage devices, and transparent electrodes. ATO nanofibers with sizes from 200 - 600 nm and a bandgap of 4.4 e.V were produced using the electrospinning method. The precursor was composed of tin chloride solution mixed with cellulose acetate solution and antimonium chloride. The XRD spectra of the nanofibers showed the characteristic peaks of Sb:SnO$_{2}$ with rutile structure. The electrical properties of single ATO nanofibers were studied following a cycle of cooling from 295 - 15 K and then heating from 15 - 295 K. These measurements were done in cold finger (close cycle helium refrigerator) in a vacuum. The conductivity measured at room temperature was 4.3 S/cm and decreases monotonically from 295 to 15K. As the temperature increases an anomalous peak is observed in the range of 250 to 300 K. This anomaly has been attributed to the chemi-absorbed molecules on the surface of the fiber and could be reduced by improving the vacuum conditions. [Preview Abstract] |
|
K1.00029: Modification of the growth mechanism of Zno nanowires by addition of oxidizing agents Eric Driscoll, Bradley Golder, Marian Tzolov Zinc oxide nanowires were grown catalytically on silicon (100) and (111) surfaces by means of chemical vapor deposition. A very thin layer of sputter deposited gold was used as the catalyst. Nanowires of different compositions were obtained by varying the ratio of carbon to zinc oxide in the source material and the flow rates of oxidizing gases. Results showed that the additional oxidizing gas changed the composition as well as the growth mode of the nanowires. The existence of several growth steps was observed. These steps were induced by the continuous presence of the source material during the system's heating and cooling processes. Remnants of gold found on the tips of the nanowires provided evidence for catalytic growth. The composition was analyzed by energy dispersive x-ray spectroscopy. Imaging by scanning electron microscopy showed random growth directions of nanowires, formation of sheets, and some instances of transitions from sheet to wire growth. The formation of defects was studied by photoluminescence spectroscopy. [Preview Abstract] |
|
K1.00030: Microstructure and Transport Studies of Functionalized Graphene Ron Gamble, Darryl Lewis, Dereje Seifu, Jorge Camacho, Myron Strongin, Liyuan Zhang The microstructure and transport studies of fuctionalized graphene are reported. These studies reveal that the minimum conductivity is sample dependent and within the range (2-12)e$^{2}$/h independent of gate voltage. The variation of the minimum conductivity is attributed to sample impurities, apparent in Atomic Force Microscopy and Raman Spectroscopy. The Raman peaks are in general consistent with graphene, but show shifts in the G and 2D peaks. These shifts are associated with strain and doping. The dependence of the current (I) on the bias voltage (V$_{SD})$ is linear for most samples. The current dependence on gate voltage (V$_{g })$curves show asymmetric behavior, showing the imbalance between the hole and electron carriers. A 16 A deposition of Fe leads to a significant modification in the transport properties due mostly the formation of iron oxide. The AFM clearly shows the formation of Fe clusters. [Preview Abstract] |
|
K1.00031: Thermal analysis study of polysterene-poly(methyl methacrylate) (PS-PMMA) diblock copolymer thin films morphologies when annealed and sheared under vacuum in inert atmosphere Luis Pomales, Melissa Davila-Santana, Mirna Rivera-Claudio, Josee Vedrine-Pauleus Diblock copolymers are made of two chemically bonded blocks, with incompatible monomers. This incompatibility gives the block the property to phase separate at temperatures above the glass transition (Tg). The ability to self-assemble into different mesophase structures is of great importance in nanolithography and nanofabrication. This research involves the morphological study of PS-PMMA thin films annealed under inert atmosphere. Our objective is to determine the microstructure properties of the PS-PMMA diblock copolymer as a function of film thickness, annealing temperature, and applied shear force. The PS-PMMA thin film is spin casted onto silicon substrates, and annealed under an inert atmosphere. Our initial results show that the samples have an incomplete formation of the microstructures. However, further film analysis is needed to study the morphological properties when annealed. Futures studies will focus on the effects of a shear force during annealing, to align the film microstructures. [Preview Abstract] |
|
K1.00032: Growth and characterization of Ba$_{8}$Ga$_{16}$Ge$_{30}$ Type I clathrate thin films grown by pulsed laser deposition Jacob Duscha, Robert Hyde, Devajyoti Mukherjee, Sarath Witanachchi Ba$_{8}$Ga$_{16}$Ge$_{30 }$thin films were successfully grown on Si (100) substrates using pulsed laser deposition process. Clathrates are studied for potential thermoelectric (TE) applications with few reports of thin film growth due to intrinsic difficulty in growing the caged structures in thin film form. Growth of stoichiometric Ba$_{8}$Ga$_{16}$Ge$_{30 }$thin films is complicated by non-congruent evaporation during the ablation process resulting in Ga or Ge deficient films, degrading their properties. We report a systematic study of the growth parameters for stoichiometric Ba$_{8}$Ga$_{16}$Ge$_{30 }$thin films. The laser ablated plasma plumes were analyzed using ICCD imaging and optical emission spectroscopy enabling optimization of growth parameters. Film thickness profiles of various target-substrate distances were plotted to estimate an optimum deposition rate. Surface morphologies and structure of the as-deposited films were examined using a scanning electron microscope and x-ray diffraction technique. This investigation provides a new direction towards the growth of high quality thin films for potential TE device applications. [Preview Abstract] |
|
K1.00033: Investigation of Silver Thin Film Reactivity via STM Jehovani Lopez, Stephen Tsui The operation of a scanning tunneling microscope (STM) to some extent is nearly as much art as it is science. A recent attempt was made to examine the surface topography of glass by depositing a thin conducting silver film over the surface via plasma sputtering. Preliminary results show our instrument's inability to image this silver. Our hypothesis is that the silver nanoparticles may react in air, thereby creating a tunneling barrier that impedes the STM current. Silver nanoparticles deposited on highly orientated pyrolitic graphite at varying layers of thickness were imaged to analyze scatter patterns and deposition. Over time, STM images of the silver nanonclusters on HOPG showed some inconsistency in the diameters of the deposited clusters, possibly due to an artifact from the suggested reactivity of the silver. To confirm this, we also investigate depositions of gold, which is nonreactive. [Preview Abstract] |
|
K1.00034: Thin Film and Free Crystallite Formation of ZnO Nanorods from Solution Under Extreme Crystallization Conditions Anamika Gopal, Chelsi Kwitoski, Marian Tzolov ZnO nanorods, grown by the established Hexamethylenetetramine (HMTA) process, through the reaction of Zinc Nitrate with HMTA, are investigated. The nanorod morphology dependence on temperature, initial solution concentration and crystallization time is studied. Crystal growth on glass and ITO substrates and free crystallite precipitation in solution are characterized by SEM and EDX. Low concentrations and temperatures are investigated for production of rod-clusters with a high aspect ratio and low surface nucleation density. Such morphology is expected to enhance charge transport while preserving light transmissivity, for use in efficient ZnO photovoltaic devices. Free crystallite formation in solution with varied initial parameters is characterized by a time dependent light scattering study, supported by SEM and EDX data. A high aspect ratio of solitary, free crystallites is sought, which we believe would be most effective in solution processed, concentration gradient solar cells. [Preview Abstract] |
|
K1.00035: Time-resolved Four-terminal probe of ion transport in Schefflera leaves Nicole Perigo, Guoping Zhang Plant growth relies on efficient ion transport. The rate of the ion transport depends on the concentration of each ion in the leaf. A common method is to use two-lead geometry. Here we employ a four-electrode set-up orienting the electrodes either parallel or perpendicular to each other. When the electrodes are parallel, two are at each end, with electric current running along the direction of the veins. When they are perpendicular, there are two along the direction of the veins (tip-tip) and two are perpendicular to the veins (side-side). The parallel set-up is similar to the Franck-Hertz experiment, but instead of using a vacuum tube we use a leaf. By using the parallel set-up, we find that two inner leads can directly control the movement of the ions in the time domain. By switching on/off the control current, a clear time-resolved current change is observed, where the signal decays less than one second. This time scale is similar to that of a typical ECG decay signal. Therefore, our method may be potentially a powerful tool to ion diffusion and transport in many biological and medical systems. [Preview Abstract] |
|
K1.00036: PHYSICS EDUCATION |
|
K1.00037: Energy-Efficient Cooking of Spaghetti Akash Levy Spaghetti is a dual-career family dinner favorite. But how much energy is consumed in the process, and how can it be optimized? I performed an experiment to test two methods for preparing a spaghetti meal. In both cases, the water was rapidly heated to the boiling point. The flame was kept at maximum for the first experiment until the spaghetti was cooked. In the second experiment, the flame was reduced and the top covered, such that the water was kept at 100C. The two methods are compared in terms of the total time required to prepare the meal and amount of energy required. A discussion of potential savings for the latter method--and possible uses for that savings--is discussed. [Preview Abstract] |
|
K1.00038: Snail Mail: Kinematics Applied to an International Letter's Seventeen-Year Journey Ishan Levy The average and instantaneous velocity of a letter sent in 1990 from India and arriving in 2007 in New York City is analyzed using the equations of kinematics. An important question to be addressed is: how does the average speed of ``snail mail'' compare with that of an actual snail? The distinction between instantaneous versus average kinematic quantities are highlighted in the process. [Preview Abstract] |
|
K1.00039: Heuristic Deduction of the Newton's Second Law Gregorio Ruiz-Chavarria, Jonas Torres-Montealban In this work we present a heuristic justification about the form of the second law of Newton. We start with a basic definition of force as the interaction between the body of study and everything that surrounds it. We define the mechanical state of a body through the momentum, because this gives us a measure of the ability to carry out an interaction. Now with this definition, the variation of the state of the body over time gives a measure of the intensity of this interaction. From this variation in time, we can establish Newton's second law. The approach described above can be used with students in pre-university and university. [Preview Abstract] |
|
K1.00040: Obtaining the Thermal Efficiency of a Steam Railroad Machine Toy According Dale's Cone of Learning Omar Tomas Bautista-Hernandez, Gregorio Ruiz-Chavarria Physics is crucial to understanding the world around us, the world inside us, and the world beyond us. It is the most basic and fundamental science, hence, our interest in developing innovative strategies supported by the imagination and knowledge to make the learning process funny, attractive and interesting to people, so, we can help to change the general idea that Physics is an abstract and complicated science. We all know this instinctively, however, turn-of-the-century educationist Edgar Dale illustrated this with research when he developed the Cone of Learning - which states that after two weeks we remember only 10\% of what we read, but we remember 90\% of what we do. Based on that theory, we obtain the thermal efficiency of a steam railroad machine -this is a toy train that could be bought at any department store-, and show you the great percentage of energy lost when moving this railroad machine, just as the real life is. While doing this practice we don't focus on the results itself, instead, we try to demostrate that physics is funny and it is not difficult to learn. We must stress that this practice was done with pre-universitary and univesitary students, however, can be shown to the community in general. [Preview Abstract] |
|
K1.00041: Statistical evidence of predation by theropods Scott Lee Dinosaurs hold a great fascination for everyone and provide an interesting venue for teaching many elementary concepts of kinematics. Dinosaur trackways provide interesting information about the locomotion of these extinct animals. A statistical analysis of the known trackways made by theropods (carnivorous dinosaurs) shows that they usually moved by walking with an average speed of 2.4 $\pm $ 1.5 m/s. Fast running, determined by the relative stride length greater than 3, is observed in about 10{\%} of the trackways, with speeds on the order of 10 m/s. These trackways are believed to have been formed during predation. [Preview Abstract] |
|
K1.00042: Surveying Students' Understanding of Quantum Mechanics Chandralekha Singh, Guangtian Zhu Development of research-based multiple-choice tests about quantum mechanics is important for assessing students' difficulties and for evaluating curricula and pedagogies that strive to reduce the difficulties. We explore the difficulties that the undergraduate and graduate students have with non-relativistic quantum mechanics of one particle in one spatial dimension. We developed a research-based conceptual multiple-choice survey that targets these issues to obtain information about the common difficulties and administered it to more than a hundred students from seven different institutions. The issues targeted in the survey include the set of possible wavefunctions, bound and scattering states, quantum measurement, expectation values, the role of the Hamiltonian, time-dependence of wavefunction and time-dependence of expectation value. We find that the advanced undergraduate and graduate students have many common difficulties with these concepts and that research-based tutorials and peer-instruction tools can significantly reduce these difficulties. The survey can be administered to assess the effectiveness of various instructional strategies. [Preview Abstract] |
|
K1.00043: Theoretical model to explain the problem-solving process in physics Carlos Lopez This work reports a theoretical model developed with the aim to explain the mental mechanisms of knowledge building during the problem-solving process in physics using a hybrid approach of assimilation- formation of concepts. The model has been termed conceptual chains and represents graphic diagrams of conceptual dependency, which have yielded information about the background knowledge required during the learning process, as well as about the formation of diverse structures that correspond to distinct forms of networking concepts Additionally, the conceptual constructs of the model have been classified according to five types of knowledge. Evidence was found about the influence of these structures, as well as of the distinct types of knowledge about the degree of difficulty of the problems. [Preview Abstract] |
|
K1.00044: Graphical representation of the process of solving problems in statics Carlos Lopez It is presented a method of construction to a graphical representation technique of knowledge called Conceptual Chains. Especially, this tool has been focused to the representation of processes and applied to solving problems in physics, mathematics and engineering. The method is described in ten steps and is illustrated with its development in a particular topic of statics. Various possible didactic applications of this technique are showed. [Preview Abstract] |
|
K1.00045: Physics Education at University of Houston Clear Lake Samina Masood We are developing a physics education program to prepare teachers to teach Physics in High Schools. The science teachers training needs to be brought to the level where they can motivate children and young adults in their classrooms to take interest in science learning to adopt science and engineering career. The early selection of career path helps the better preparation for the career. [Preview Abstract] |
|
K1.00046: GENERAL THEORY (THEORETICAL METHODS) |
|
K1.00047: Variational Study of a Finite Heisenberg Chain Eric Ashendorf, Joe Weiner, Jay D. Mancini, Vassilios Fessatidis, Samuel P. Bowen Here we wish to study the ground-state of the $1D$ Heisenberg chain% \[ H=-\frac{1}{2}J\sum_{l=1}^{N}\left[ 2\left( \sigma_{l}^{+}\sigma_{l+1}% ^{+}+\sigma_{l}^{-}\sigma_{l+1}^{-}\right) +\sigma_{l}^{z}\sigma_{l+1}% ^{z}\right] , \] where the $\sigma$'s are the usual Pauli spin matrices and $J$ is the strength of the spin-spin interaction. The purpose of our revisiting such a well known system is to use it as a benchmark for our variational ansatz in which a trial vector is chosen $\left\vert \psi_{0}\left( \alpha\right) \right\rangle =\exp\left( \alpha\sum_{l=1}^{N}\sigma_{l}^{+}\sigma_{l+1}^{z}\right) \left\vert 0\right\rangle _{N}$, where $\alpha$ is the variational parameter and $\left\vert 0\right\rangle _{N}$ is an appropriately chosen initial array of spins. We then construct a basis according to the prescription $\left\vert \psi_{m}\right\rangle =\partial_{\alpha}^{m}\left\vert \psi_{0}\left( \alpha\right) \right\rangle $ creating an energy matrix with elements $h_{ij}=h_{ij}\left( \alpha,J\right) $ whose eigenvalues are then evaluated. [Preview Abstract] |
|
K1.00048: Anharmonic Energy Spectrum for $V(x)=\pm x^{4},\pm x^{6},\pm x^{8}$ Samuel P. Bowen, Jay D. Mancini, Vassilios Fessatidis In this work we wish to revisit the energy spectrum for the anharmonic potentials% \[ H=\frac{p^{2}}{2m}\pm x^{N}, \] where $N=4,6,8$. Using the second quantized operator formalism of Dirac, we have evaluated matrix truncations of up to $100\times100$. Our results for the energy spectrum are in disagreement with the work of Bender and Boettcher (PRL 80, 5243). They studied a \emph{PT} symmetric Hamiltonian whose potential is given by $V(x)=-(ix)^{N}$ and who maintain that \textquotedblleft when $N\geq2$, the spectrum is infinite, discrete and entirely real and positive\textquotedblright. We find, for the potentials with $N=4,6,8$ that the spectrum is not completely positive and in fact has no lower bound. [Preview Abstract] |
|
K1.00049: Moments based calculations of PT-symmetric Hamiltonians Robert Murawski, Jay Mancini, Vassilios Fessatidis PT-symmetric Hamiltonians have gained recent interest in optics and particle physics [Phys. Rev. A \textbf{82}, 031801 (2010), Phys. Rev. Lett. \textbf{105}, 031601 (2010)] . These Hamiltonians remain invariant under the reflection of parity and time. What makes them surprisingly interesting is that PT-Hamiltonians have real positive spectra. In this paper, we calculate the moments of the PT Hamiltonian H=p$^{2}$+x$^{2}$ (ix)$^{r}$ with r$>$0. We will use these moments to compute the ground state energy by the generalized moments expansion (GMX) and the canonical sequence method (CSM). Comparisons will be made to the Lanczos tridiagonalization scheme as well as to other published results. [Preview Abstract] |
|
K1.00050: Ab initio approach to magnon-electron coupling Pawel Buczek, Arthur Ernst, Leonid M. Sandratskii, Hardy Gross \newcommand{\el}{\textit{et~al}.} The electronic properties of magnets and exchange-enhanced paramagnets are strongly influenced by the spin-flip fluctuations. In particular, their important role in the pnictide high-temperature superconductivity is has been conjectured [Mazin \& Johannes, \textit{Nat. Phys.} \textbf{5}, 141 (2009)]. To formulate a parameter free model of electron-electron interaction involving emission and absorption of magnons we combine our recently developed implementation of the linear response time dependent density functional theory for spin fluctuations [Buczek \el, \textit{Phys. Rev. Lett.} \textbf{105}, 097205 (2010)] with the methods of many body perturbation theory [Vignale \& Singwi, \textit{Phys. Rev. B} \textbf{32}, 2156 (1985); Zhukov \el, \textit{Phys. Rev. Lett.} \textbf{93}, 096401 (2004)]. This theoretical toolbox is applied to the description of recent inelastic tunneling spectroscopy experiments [Balashov \el, \textit{Phys. Rev. Lett.} \textbf{97}, 187201 (2006)], which have shown that the emission of magnons by electrons can open additional tunneling channels and increase conductivity. As second application, we discuss a scheme of the magnon mediated Cooper pair formation in PdH$_{x}$ and LaFeAsO. [Preview Abstract] |
|
K1.00051: Classification of Gapped Symmetric Phases in 1D Spin Systems Xie Chen, Zheng-Cheng Gu, Xiao-Gang Wen Topological phases exist in quantum many-body systems beyond the usual symmetry breaking understanding of phase and phase transition. The question of what kind of topological phases exist seems hard especially for strongly interacting systems. Here we make an attempt to answer this question for gapped interacting quantum spin systems whose ground states are short-range correlated. Based on the local unitary equivalence relation between short-range correlated states in the same phase, we classify possible quantum phases for 1D matrix product states, which represent well the class of 1D gapped ground states. We find that in the absence of any symmetry all states are equivalent to trivial product states, which means that there is no topological order in 1D. However, if certain symmetry is required, many phases exist with different symmetry protected topological orders. Understanding about topological order and symmetry breaking order in spin systems also allows us to obtain a classification of 1D fermion topological phases. [Preview Abstract] |
|
K1.00052: Effective equilibrium theory of non-equilibrium quantum transport Prasenjit Dutt, Jens Koch, Jong Han, Karyn Le Hur We establish a rigorous theoretical foundation for an effective equilibrium description of electronic transport through quantum impurity models out of equilibrium. An imaginary time framework involving the Lippmann-Schwinger operators of the system is proposed and expounded. This forms the basis for the implementation of standard equilibrium many body techniques, effectively avoiding the complexities of the Keldysh contour, and is used to compute transport observables. We present a novel perturbative scheme for treating interactions, which we use to study the Anderson impurity model out of equilibrium. Generalizations to non-perturbative methods are also explored. We use this formalism to investigate the effect of voltage bias, temperature and a magnetic field on the fate of the Abrikosov-Suhl resonance and make a comparison with numerics and experimental results. [Preview Abstract] |
|
K1.00053: Magnetic properties of CuZrTiO$_{5}$ H.M. Alyahyaei, R.A. Jishi, D.M. Guzman, O. Ta, A.A. Sharif CuZrTiO$_{5}$ is a newly synthesized crystal that contains copper oxide planes $^{[1]}$. We have carried out first-principles calculations using density functional theory in order to determine the ground state of this crystal. We considered various nonmagnetic and magnetic phases and calculated the corresponding total energies. We found that in the ground state, the magnetic moments on the copper ions adopt an antiferromagnetic arrangement. The effects of doping on the electronic properties of this crystal are investigated. \\[4pt] [1] U. Troitzsch et al., Journal of Solid State Chemistry 183, 668(2010). [Preview Abstract] |
|
K1.00054: Vacillation in density of correlated electron-electron pair confined in 2D quantum dot Takuma Okunishi, Atsushi Tsubaki, Tomoki Tagawa, Kyozaburo Takeda We studied an electronic structure of charged particles confined in a 2D quantum dot (QD), taking into account an electron correlation through a configuration interaction (CI) by employing resonating unrestricted Hartree-Fock (res-UHF) approach. The UHF solutions for the QD are nonorthogonal mutually but are appropriate for a basis functions of a res-UHF CI calculation because they represent a conceivable electron- spin configurations rationally. Consequently, the res-UHF CI provides intuitive understandings for an electron correlation with narrowing down the number of employed Slater bases, although at an expense of orthogonality among the Slater bases. We further embedded this res-UHF CI approach to solve a time- dependent (TD) Schroedinger equation, and studied the TD features caused by an electron correlation computationally. We found that the electron correlation induces the characteristic vacillation in the total charge density. We then employed a projection analysis and investigated the change in the vacillation frequencies by varying the confinement length and also the initial charge distribution. [Preview Abstract] |
|
K1.00055: Ground state instability in spin polarization for electrons confined in 2D square quantum dots Kyozaburo Takeda, Masamu Ishizuki, Takuma Okunishi, Yhuki Negishi We present a theoretical study of the ground state electronic structure and the spin polarization for four electrons confined in 2D square quantum dots (2D SQDs). We employ standard mean field theory (MFT) approaches using the unrestricted Hartree-Fock (UHF) and density functional theory (DFT) calculations. The resonant UHF configuration interaction (res-UHF CI) calculation was also performed in order to understand the electron correlation more intuitively. The MFT ground state is expected to be fully spin-polarized when square SQDs have a small confinement length L or aspect ratio, in agreement with Hund's rule. In contrast, the spin-unpolarized ground state singlet is expected in all in other SQDs, the MFT anti-Hund state is produced by the spin-density wave having the zero total spin. The res-UHF CI calculation restores the geometrical symmetry in the resulting ground state, but the res- UHF CI ground state maintains the zero total spin. Thus, ground state instability is expected in the spin-polarization of the SQD system, which eventually violates Hund's rule in accordance with the Coulomb interaction. [Preview Abstract] |
|
K1.00056: Real-space Green's function calculations of valence Compton profiles for Nonresonant Inelastic X-ray Scattering Brian Mattern, Joshua Kas, John Rehr Nonresonant inelastic x-ray scattering (NIXS) from core- and semi-core shells at 50-1000 eV binding energies is an emerging field of synchrotron light source science, with applications in high pressure science, electrical energy storage, f-electron materials, and catalysis, etc. In such experiments, the Compton scattering of x-rays by valence electrons produces a significant background signal that spans the energy loss range of interest for NIXS. Thus, first-principles theoretical calculations of the double-differential cross-section for Compton scattering in the energy loss and momentum transfer ranges of interest are needed to account for this background. Here, we report an approach using a real space Green's function method to calculate the valence Compton profile in the impulse approximation. Illustrative calculations are presented and compared with experiment. [Preview Abstract] |
|
K1.00057: Exchange-correlation energy functionals for low-dimensional electronic nanostructures: Recent developments and applications Stefano Pittalis, E. R\"as\"anen, C.A. Rozzi, G. Vignale In the analysis of low-dimensional electronic nanostructures, the evaluation of the consequence of the electron-electron interaction is a challenging task. In particular, an accurate determination of the exchange-correlation energy in two-dimensional systems is of great importance in understanding the many-body physics of modern electronic devices. Here we review several approaches within density functional theory, spanning from the bottom to the top of the ladder of functional approximations. Considering applications to quantum dots, rings, slabs, and periodic systems, we conclude that the presented approaches form a valuable first-principle toolkit for dealing with the many-body physics of such devices. [Preview Abstract] |
|
K1.00058: Exchange energy and potential using the Laplacian of the density Chris Wagner, Antonio Cancio abstract- The challenge of density functional theory is the useful approximation of the exchange correlation energy. This energy can be approximated with the local electron density and the gradient of the density. Many different GGA's have been made recently and there is controversy over the best overall functional. Recent Monte Carlo simulations give evidence that the Laplacian of the density might be a better starting place than the gradient to correct the local density approximation. It also gives a better representation of the exchange potential at the nuclear cusp and of bonding between atoms. We have tested several Laplacian based GGA models for exchange for small atoms. We use known constraints on the exchange energy used in current GGA's. In many models unphysical oscillations occur in the potential, and understanding and eliminating them is part of the focus of this research. Preliminary results suggest that smaller values for short and long range constraints in the literature give more physically reasonable results in the Laplacian models. [Preview Abstract] |
|
K1.00059: Hybrid Density Functional Studies of a Promising Photovoltaic Material: Zinc Phosphide Steven Demers, Axel van de Walle Although Zinc phosphide is a semiconductor which has high absorption in the visible spectrum that is made from abundant elements, its use as a low-cost photovoltaic is limited by difficulties in n-doping the material. We study this compound via Density Functional Theory calculations based upon recently developed hybrid functionals designed to accurately describes band gaps. We explore the effects of various point defects with energy levels near the fermi energy on the electronic band structure in an effort to identify suitable dopants in this system. The thermodynamic stability of these defects is also assessed. [Preview Abstract] |
|
K1.00060: Mass-Energy Relationship Must Include Factors For Vibrational and Rotational Kinetic Energies as Well as Various Potential Energies Stewart Brekke Einstein proposed that at low speeds $E=M_0c^2 + 1/2M_0v^2$. However, a mass may also have vibrating and rotating kinetic energies and may also have various potential energies such as gravitational, electric and magnetic potential energies which must be part of the total mass-energy equivalence. Therefore, the basic equation for the mass-energy equivalence should be $E=M_0c^2 + 1/2M_0v^2 + 1/2I\omega^2 + 1/2kx^2 + (GM_0M_2)/r + (KQ_0Q_2)/r +(Um_0m_2)/r$ where the last three terms are the gravitational, electrostatic and magnetic potential energies of the mass and the second, third and fourth terms are the linear, rotational and vibrational kinetic energies of the mass.Also, Einstein did not include the rotational and vibrational kinetic energies in his relationship for relativistic kinetic energy and therefore the kinetic energy T cannot equal $(E-E_0) =1/2M_0v^2$, but rather must equal $T=1/2M_0v^2 + 1/2I\omega^2 + 1/2kx^2$ including the vibrational and rotational kinetic energies besides the linear kinetic energy alone. [Preview Abstract] |
|
K1.00061: A Theory of Frozen Light According to the General Theory of Relativity Dmitri Rabounski, Larissa Borissova We suggest a theory to frozen light, which was first registered in 2000 by Lene Hau. Frozen light is explained here as a new state of matter. The explanation is given through space-time terms of the General Theory of Relativity. We consider a fully degenerate region of space (space-time), which is the ultimate case of the isotropic region (home of photons), where the metric is particularly degenerate. Both the space-time interval, the observable time interval, and the observable three-dimensional interval are zero in a fully degenerate region. Therefore, we refer to such a region and particles which inhabit it as zero-space and zero-particles. Moving to the coordinate quantities inside zero-space shows that real speed therein is that of light, depending on the gravitational potential and the rotation of space. It is shown that the eikonal equation for zero-particles is a standing wave equation: zero-particles are standing light waves, while zero-space is filled with a system of standing light waves (light-like hologram). With these, zero-particles appear to a regular (external) observer as mere stopped light. This paper has been submitted to The Abraham Zelmanov Journal. [Preview Abstract] |
|
K1.00062: Symplectic Integrator and its Applications Hiroto Kobayashi The first- and the second-order symplectic integrators for the one-dimensional harmonic oscillator are reconstructed on the basis of effective Liouville operators, which can be defined only within the convergence radius. The first-order one for the $q^4$-potential system breaks down for different time steps depending on the initial condition, which indicates that no conservation value exists for the system in the first- order symplectic integrator. [Preview Abstract] |
|
K1.00063: Interacting many-body simulations including contacts using graphics processing units (GPU) Tobias Kramer Already the solution of the interacting classical many-body problem is difficult to achieve, since the integration of the equations of motions couples all positions of the particles contained in the system. Transport calculations require to include the contacts within the simulation and to study the effect of interactions there. Classical and quantum-mechanical equations of motions can be related by the time-dependent variational principle for Coulombic interacting electrons in a magnetic field [1]. Interacting systems require to carefully consider the questions of self-consistency. The emergence of an mean-field potential out of a large (10000 electrons!) many-body calculation is shown in [2]. The calculation is only possible due to our usage of graphics processing units, which are ideal tools to study interacting systems. \\[4pt] [1] Two interacting electrons in a magnetic field: comparison of semiclassical, quantum, and variational solutions, T. Kramer, AIP in press (2010), arxiv:1009.6051 \\[0pt] [2] Self-consistent calculation of electric potentials in Hall devices, T. Kramer, V. Krueckl, E. Heller, and R. Parrott Phys. Rev. B, 81, 205306 (2010) [Preview Abstract] |
|
K1.00064: Intermediate size ZnS cages : energetics and stability Jose Rodriguez Lopez, Rajendra Zope, Tunna Baruah We have studied intermediate size (ZnS)$_n$ cages (n=12, 16,24,36,48, and 96) using density functional theory. Such cage structures have been observed previously in classical molecular dynamics simulations. Our DFT calculations show they these structures are energetically stable. We have further calculated the vibrational frequencies of these cages. Our vibrational analysis show that these cages are local minima on the potential energy surface. The (ZnS)96 has a onion-like structure. We have also calculated the molecular electrostatic charges on the Zn and S atoms to study the ground state charge transfer to determine the ionicity of the ZnS bonds. The quasiparticle and the lowest singlet gaps are obtained using the delta-SCF and time dependent density functional theory. [Preview Abstract] |
|
K1.00065: Mesoscale simulation of the rheology of high molecular weight polymer gels Yelena Sliozberg, John Brennan, Timothy Sirk, Jan Andzelm Polymer gels are comprised of physically or chemically cross-linked polymers that are highly swollen with solvent. The rheology of these gels depends on their morphological properties, such as the number of bridging chains and trapped entanglements. The prediction of structural and mechanical properties of gels using computational approaches is challenging and requires advanced particle-based mesoscale methodologies. Recently, we have implemented an approach to predict mechanical properties of high molecular weight block copolymers by allowing for chain entanglement behavior within the dissipative particle dynamics (DPD) methodology. Diffusion coefficients have been evaluated to locate the crossover from the Rouse to reptation dynamics. In this talk, we will demonstrate that including a segmental repulsive potential in addition to the usual DPD framework can prevent chain crossings and leads to an improved representation of mechanical and structural properties of polymer gels. [Preview Abstract] |
|
K1.00066: Resiliency of the Mixed-State Wigner Function Tomas Materdey Numerical solution of the quantum Vlasov equation showed details of the phase-space dynamics of the Wigner function. Resiliency of the mixed-state Wigner function over changes of external electric and magnetic fields will be discussed. [Preview Abstract] |
|
K1.00067: Perhaps Gravitational Waves do not Exist Orvin Wagner I have recently been working with waves that appear to penetrate everything including mountains. I call these waves ``waves in dark matter'' because of their penetrating qualities. These waves seem to indicate that dark matter interacts more than just with gravity and may be important in supporting life, for example. These waves may dissipate energy in binary orbitting systems, such as paired pulsars, and explain their orbital decay. Many authors, including Einstein, provide supporting evidence that gravitational waves do not exist. Recent experiments indicate the same. See the website: ``Darkmatterwaves.com'' [Preview Abstract] |
|
K1.00068: The mass, energy, space and time systemic theory-MEST-energy balance system of wave-particle duality Dayong Cao The paper suppose that the probability of displacement is the space and the probability of cycle is the time. And accroding to the quantum mechanics, the paper get the equation of the space : $S=P(r)={f^2}$, (1) Among it, S: the space, f: the amplitude of wave, r: the displacement, P(r): probability function of displacement. Accroding to the Benford's law, the paper get the equation of the time equation: $T=P(2{\pi}t)=ln(1+\frac{1}{2{\pi}t})={\nu}$, (2) Among it, T: the real time, t: date of clock, $\nu$: the frequence of wave, P(t): probability function of date of the clock. $E=h\nu$, (3) $m=\frac{h}{{\lambda}{c}}$, (4) Among it, E: the energy of particle, m: the mass of particle, c: the velocity of particle, $\nu$: the frequence of particle, $\lambda$: the wavelengh, h: the Planck constant. $E'{\psi}=i{\hbar}\frac{\partial{\psi}}{{\partial}t}$, (5) $m'{\psi}=-i{\hbar}\frac{{\partial}{\psi}{\partial}t} {{(\partial}x)^2}$, (6) Among it, $E'\psi$: the energy of wave, $m'\psi$: the mass of wave, c$'$: the velocity of wave, ${\psi}$: the Wave Functions. The paper give new idea that unlike mass repel each other, like mass attract; And like energy repel each other, unlike energy attract. So there is a mass-energy duality too. The energy radiate the repulsive (energy) wave and the mass absorb the absorptive (mass) wave. And there is a balance system between the energy wave and mass wave. $E+E'{\psi}=mc^2+m'{\psi}c'^2, (c'^2=-\frac{({\partial}x)^2}{({\partial}t)^2})$, (7) [Preview Abstract] |
|
K1.00069: Computational study on ionic diffusion and dynamic properties in silicate and bioactive glasses Ye Xiang, Jincheng Du Ionic diffusion and dynamic properties in silicate glasses have been extensively studied experimentally due to its importance in understanding ion conduction and glass dissolution. In this study, computational study on ionic diffusion and dynamic properties was carried out using molecular dynamics simulations with effective partial charge potentials. The simulated structure models were validated by comparing with experimental data and systematic discussions on effects of system size, simulation thermal ensemble and temperature range were carried out. The dynamic properties were also related to structural changes with the glass. Finally, investigation of SrO/CaO substitution effect on the diffusion behaviors in 45S glasses is provided. [Preview Abstract] |
|
K1.00070: ENERGY RESEARCH AND APPLICATIONS |
|
K1.00071: Optimization of open circuit voltage in parallel solar cell tandems Alexander Kuznetsov, Anvar Zakhidov Significant improvement of the solar cell efficiency is achieved by combining solar cells into tandems. Matching of the open circuit voltages (V$_{oc})$ of individual cells is required in order to maximize the efficiency of the parallel tandem. However practically it is hard to achieve because usually individual cells of the tandem absorb light at different wavelengths and produce very different V$_{oc}$. Mismatch of open circuit voltages results in deteriorated performance of a parallel tandem. In this work we use circuit analysis to determine parameters of parallel tandem's individual cells that guarantee its most efficient operation. The results of our calculations can be used for optimization of individual solar cells when designing a parallel tandem. [Preview Abstract] |
|
K1.00072: Degradation of CIGS Devices Studied using Controlled Moisture Ingress Rajalakshmi Sundaramoorthy, John Pern, Jian Li, Tim Gessert The damp heat (DH) study at 85\r{ }C and 85{\%} relative humidity of unencapsulated standard CIGS devices fabricated at NREL exhibited various degradation modes. In the initial 20 h of exposure there is a steep decrease in efficiency, followed by a gradual decrease until 1000 h. The devices in this study were subjected to controlled moisture ingress. Periodic light and dark current-voltage (JV), capacitance-voltage (CV) measurements were carried out before, during, and after the course of exposure. Initial trends in CV and JV data show that the decrease in the device performance correlates to the degree of degradation of the TCO and the buffer layer during the first 20 h of exposure. However, from 20-100 h of exposure the abrupt changes in CV and decrease in Voc suggest the moisture penetration deeper into the junction which might alter junction interface. This paper attempts to correlate the JV and the CV data to understand the degradation mechanism during the initial hours of DH exposure in CIGS devices. [Preview Abstract] |
|
K1.00073: Tunable Surface Energy Morphologies of P3HT-PCBM Bulk Heterojunction OPV's Abul M.A. Huq, Alamgir Karim In this study we used the commonly studied blend of Phenyl-C61-butyric acid methyl ester (PCBM) and Poly(3-Hexylthiophene) (P3HT) and studied their morphological development (1:1 ratio) under different substrate surface energy conditions. Confined and tunable surface energy can direct the morphology of immiscible blends which can be successfully utilized to gain desired properties of the semiconducting organic materials. We first show that solvent and temperature of film casting have equally dominant effect on the final P3HT:PCBM morphology. We observe that P3HT crystal size and size distribution depend upon the nature of substrate, thickness of the film, temperature of casting solution, and overall blend concentration in solvent. We can also tune P3HT:PCBM morphology by sandwiching the blend films between two PDMS films with well defined surface energies. These studies offer insights for development of highly controlled bulk heterojunction morphology for improving the efficiency of organic photovoltaics (OPVs). [Preview Abstract] |
|
K1.00074: Markedly Enhanced Performance of Dye Sensitized TiO$_{2}$ Nanoparticle Solar Cells via Rational Surface Treatment Margaret Scheiner, Xukai Xin, Zhiqun Lin Dye sensitized solar cell (DSSC) was fabricated with the P-25 TiO$_{2}$ nanoparticle film sensitized with N719 dye. TiCl$_{4}$ treatment was found to increase the power conversion efficiency of DSSC. More importantly, subsequent treatment with O$_{2}$ plasma further enhanced the efficiency, while the O$_{2}$ plasma processing of an untreated TiO$_{2}$ photoanode resulted in a lower efficiency. With TiCl$_{4}$ and O$_{2}$ plasma treatments, dye sensitized TiO$_{2}$ nanoparticle solar cell with 21 $\mu $m thick active layer illuminated under 100 mW/cm$^{2}$ exhibited a markedly enhanced power conversion efficiency of 8.35{\%} as compared to 3.86{\%} for untreated cells. [Preview Abstract] |
|
K1.00075: Structural and Electrical Characterization of Pulsed Laser Deposited CdS/CdTe Thin Films Michael Newby, M. Alper Sahiner, Samuel Emery, Michelle Jamer, Jeffrey Serfass, Mark Croft The thin films of CdS/CdTe were deposited on ITO coated glass substrates using pulsed laser deposition (PLD). The film growth conditions were systematically varied and the thin film structural properties were determined using a x-ray diffraction (XRD) x-ray absorption spectroscopy (XAS). The effect of the thicknesses of the CdS and CdTe layers, laser energy and the deposition temperature on the film quality and structure were investigated. The photovoltaic properties of the film were then tested using a Keithley sourcemeter and an accompanying Labview program. The results of variation of thickness and growth conditions on the photovoltaic output of the films will be presented. [Preview Abstract] |
|
K1.00076: Monte Carlo Simulations for Charge Transport in Bulk-Heterojunction Solar Cells: Effect of Morphology on Charge Carrier Mobility Young Min Nam, Won Ho Jo Although it is well understood that the nano-scaled morphology of active layer is critical for determining the efficiency of bulk-heterojunction solar cells, the effect of the variation in morphology upon the local mobility of charge carriers and the performance of solar cell has largely been unknown. Since the computer simulation is a powerful method to provide important information for the relationship between mobility and morphology, we use a Monte Carlo to reveal the dependence of mobility upon the morphology. As the domain size and the blend composition of morphology across the active layer are systematically varied, the mobility of charge carriers and the solar cell performance are calculated. The result of simulation reveals that the charge carrier mobility and the performance of solar cell improved largely due to the efficient extraction of charge carriers at the electrodes, when the domain size is optimized and the blend composition becomes donor-rich at the anode and acceptor-rich at the cathode. [Preview Abstract] |
|
K1.00077: Exciton Energy Transfer from Halide Terminated Nanocrystals to Graphene in Solar Photovoltaics Obafunso Ajayi, Justin Abramson, Nicholas Anderson, Jonathan Owen, Yue Zhao, Phillip Kim, Felice Gesuele, Chee Wei Wong Graphene, a zero-gap semiconductor, has been identified as an ideal electrode for nanocrystal solar cell photovoltaic applications due to its high carrier mobility. Further advances in efficient current extraction are required towards this end. We investigate the resonant energy transfer dynamics between photoexcited nanocrystals and graphene, where the energy transfer rate is characterized by the fluorescent quenching of the quantum dots in the presence of graphene. Energy transfer has been shown to have a d$^{-4}$ dependence on the nanocrystal distance from the graphene surface, with a correction due to blinking statistics. We investigate this relationship with single and few layer graphene. We study halide-terminated CdSe quantum dots; where the absence of the insulating outershell improves the electronic coupling of the donor-acceptor system leads to improved electron transfer. We observe quenching of the halide terminated nanocrystals on graphene, with the quenching factor \textit{$\rho$} defined as$ I^{Q}/I^{G}$ (the relative intensities on quartz and graphene). [Preview Abstract] |
|
K1.00078: ABSTRACT WITHDRAWN |
|
K1.00079: Electrical and Optical Properties of ITO thin films prepared by Dual Ion Beam Sputtering Alan Woodall, Wim Geerts, Anup Bandyopadhyay Indium Tin Oxide (ITO) thin films find application as transparent electrodes in photodetectors and solar cell devices. We prepared ITO thin films by dual ion beam sputtering from an ITO target on glass microscope slides. During the deposition the substrate was exposed to an atomic oxygen beam. We investigated the influence of the oxygen flow and RF power on the optical and electrical properties of the thin films. The substrates were cleaned ultrasonically in IPA prior to being loaded in the vacuum system (background pressure in 1E-7 torr range). The argon sputtering pressure as well as the beam and acceleration voltages were kept constant during deposition. The RF power of the assist beam was kept at 200 Watt. The oxygen atomic beam was varied by varying the oxygen flow from 0 to 5 sccm. The RF power of the main gun was varied from 64 to 110 Watt. The resistivity of the samples were measured by linear 4pp. The optical properties of the samples were measured by transmission spectroscopy and ellipsometry. The resistivity and the absorption of the films appeared to be minimum at 5 sccm and 86 Watt. [Preview Abstract] |
|
K1.00080: DNA-Templated Synthesis of Pt Nanoparticles on Single-Walled Carbon Nanotubes and their Electrocatalytic Properties Qianqian Liu, Lifeng Dong Platinum (Pt) supported on single-walled carbon nanotubes is one of the most efficient catalysts for both methanol and ethanol electroxidations. However, there is lack of a facile and environmental method to synthesize Pt nanoparticles on SWCNTs. In this study, we investigated a novel method to synthesize Pt nanoparticles on SWCNTs using DNA molecules as dispersing agent for nanotubes and templates for Pt nanoparticles. Morphology and structure of Pt nanoparticles and their distributions along SWCNTs as well as interactions between SWCNTs and DNA molecules were studied with the use of scanning electron microscopy, transmission electron microscopy, UV-vis spectroscopy, and X-ray diffraction spectrometer. Electrocatalytic activities of Pt nanoparticles for methanol and ethanol oxidations were characterized using cyclic voltammetry and impedance spectroscopy. With this study, we conclude effects of DNA molecules on synthesis of Pt nanoparticles on SWCNTs and electrocatalytic activity of Pt nanoparticles supported on SWCNTs for methanol and ethanol oxidations. [Preview Abstract] |
|
K1.00081: High density H2 associative absorption on Titanium alpha-borozene (Ti2B6H6): An ab-initio case study Alireza Akbarzadeh, C.J. Tymzcak Hydrogen is considered as a clean energy carrier that could be a future replacement for our addiction to fossil fuels. However, in order to have hydrogen economy at its highest efficiently we need to store hydrogen at high volumetric and gravimetric density. Using the all electron hybrid density functional theory, we have designed a benzene-like-molecule, Ti2B6H6, which has the promise of achieving this goal. Our results show that the molecule can associatively absorb the hydrogen up to ten percent by weight of hydrogen, which exceeds the 2015 US department of energy target. In this presentation we will discuss the mechanisms of H2 absorption and possible applications of this novel molecule. [Preview Abstract] |
|
K1.00082: First-Principles Study of LiPON Solid Electrolyte Santosh K.C., Ka Xiong, Kyeongjae Cho There has been much interest in the thin-film solid electrolyte for solid state battery and ionics applications. LiPON is a representative material developed by Oak Ridge National Laboratory [1]. In this work, we use first principles calculations based on the density functional theory to investigate the Li- ion migration mechanisms of LiPON family materials [2]. We investigate atomic structures, electronic structures and defect formation energies of these materials. To determine the migration path of Li diffusion, the activation energies are calculated. This study helps us to understand fundamental mechanisms of Li-ion migration and to improve Li ion conductivity in the solid electrolytes. \\[4pt] [1] Patil et al, Material Research Bulletin, 43 (2008) 1913-1942. \\[0pt] [2] Yaojun A. Du and N. A. W. Holzwarth, Physical Review B, 81 (2010). [Preview Abstract] |
|
K1.00083: Electrical and electrochemical characterization of nano-sized LiFePO$_{4}$ cathode materials synthesized by a lauric acid-based sol--gel method Khadije Bazzi, Ambesh Dixit, M. B. Sahana, C. Sudakar, M. Nazri, P. P. Vaishnava, V. Naik, G. A. Nazri, R. Naik We synthesized pure LiFePO$_{4}$ and C-LiFePO$_{4}$ nanoparticles by sol-gel technique. Carbon coating was accomplished by including Lauric acid in the sol-gel precursor solution. Three C-LiFePO$_{4}$ samples of particle sizes 29, 27, 23 nm, were prepared by varying lauric acid concentration in the precursor solution.~ All the samples were~characterized~by X-ray diffraction, Raman, conductivity, and electrochemical measurements. The micro-Raman measurements showed two major bands at $\sim $1585 cm$^{-1}$ (G) and at $\sim $1345 cm$^{-1}$ (D) in all the C-LiFePO$_{4}$ samples.~ The 23 nm particle size sample showed minimum (D/G) band ratio and the maximum electrical conductivity among the three samples. The measured value of the capacity for 23 nm sized sample,~$\sim $170 mAh/g, approached the theoretical capacity limit value for LiFePO$_{4}$ [Preview Abstract] |
|
K1.00084: Templated electrodeposition of nanoporous silicon for battery applications Stephanie Lim, Karine Namur, Florie Martineau, Jeremy Mallet, Jiabin Liu, Qian Wu, Han-Chang Yang, X. M. Cheng While battery technology has improved greatly in the last several years, the ability of batteries to store energy is still small compared to that of fossil fuels. In lithium ion batteries, the key issue is insufficient energy density, which is related to the interfacial surface area of the battery electrode. There is an urgent need to develop high capacity electrode materials and among the most promising candidates are Si based anode materials with specific energy capacities up to ten times greater than those of conventional graphite-based materials. We report the fabrication of nanoporous Si using templated electrochemical deposition method. The fabrication involves the following steps: self-assembly of monodispersed polystyrene spheres, electrochemical deposition of Si into the self-assembled template, and sphere removal by a dissolution process. The pore size of the nanoporous Si was tuned by using various sizes of template polystyrene spheres. Scanning electron microscopy images confirmed the high porosity of the samples. The templated electrochemical deposition technique provides a promising alternative approach to preparing highly porous anode materials for battery applications. [Preview Abstract] |
|
K1.00085: Li ion migration of lithium thiophosphate solid electrolyte materials Roberto Longo Pazos, Ka Xiong, Weichao Wang, Kyeongjae Cho Li$_{2}$S-P$_{2}$S$_{5}$-based glasses are of great interest to be used as electrolytes in solid-state batteries. However, a detailed understanding on their structures and diffusion mechanisms is still missing. In this work, we investigate the atomic structures and ion diffusion mechanisms of various thiophosphate composites. These materials show intriguing structural similarities to their analogous Li phosphates. As a high ion conductivity battery material, interstitial and vacancy Li point defects should be reasonably stable within the host system. Besides, system with charged defect must be insulating to prevent electronic conduct which may low the ion conductivity. Our results show that interstitial Li has lower formation energy than Li vacancy, thus indicating that the ion conductivity may arise from the migration of interstitial Li. We propose possible solutions to optimize it. This study will help us to gain fundamental understanding on the Li ion diffusion process. [Preview Abstract] |
|
K1.00086: Simulating Dendritic Formation and Possible Prevention Within Lithium-ion Batteries Joseph Ortiz, Arpon Raksit, Ning Sun, Dilip Gersappe As technology advances and becomes more dependent on lithium-ion batteries for power, the formation and subsequent separation of dendrites along the cathode may shorten the lifespan and efficiency of these batteries. However, not much is known about the mechanisms that cause dendrite formation within the battery or how to prevent their occurrence. Using a three-dimensional lattice-Boltzmann simulation, a lithium-ion battery was simulated that would allow for dendritic formation and separation. The simulation was carried out using several pre-existing cathode morphologies, and the hindrance and prevention effects of these changes were examined. [Preview Abstract] |
|
K1.00087: Luminescent Properties of Ca$_{3}$Sc$_{2}$Si$_{3}$O$_{12}$: Mn$^{2+}$ and Ce$^{3+}$ for a White LED William Coggins, Jessica Lang, Li Ma In this experiment, we studied the excitation and emission properties, as well as the fluorescence decay of the doubly doped Ca$_{3}$Sc$_{2}$Si$_{3}$O$_{12}$: Mn$^{2+}$ and Ce$^{3+}$ phosphor. The phosphor is coated on a GaN LED chip, and the Mn$^{2+}$ and Ce$^{3+}$ centers give red and green emissions, respectively, subject to the blue excitation from the chip. Together with the transmitted blue light from the LED chip, the system yields an ideal white light, with a potential application for lighting. The red emission from Mn$^{2+}$ ions has a longer decay time than that of the green emission from the Ce$^{3+}$. The color composition and stability along with the input power have also been studied. [Preview Abstract] |
|
K1.00088: Measuring Wall Insulation Beth Parks, Kevin Kurkel, Amanda Zranchev, Clayton Brown Currently, the only way for homeowners to learn about the effectiveness of their home insulation is to hire an energy auditor. This difficulty deters homeowners from taking action to improve energy efficiency. We have developed a simple device to measure wall insulation by measuring the temperature difference between the wall surface and the interior air. This device is effective in diagnosing cases of low insulation. [Preview Abstract] |
|
K1.00089: Introduction to SC-Potential Florentin Smarandache, Victor Christianto A new type of potential for nucleus, which is different from Coulomb potential or Yukawa potential, is introduced. This new called Smarandache-Christianto potential may have effect for radius range within r = 5-10 fm. For experimental verification of this potential, we find possible applications in the context of Condensed Matter Nuclear reaction. According to Takahashi's research, it is more likely to get condensed matter nuclear reaction using cluster of deuterium (4D) rather than using D+D reaction (as in hot-fusion, in this process Coulomb barrier is very high). In recent work, Takahashi shows that in the TSC framework it is also possible to do CMNS reaction not only with DDDD, but also with DDDH, DDHH, DHHH, or HHHH, where the reaction can be different. In other words, TSC can be a mixture of heavy and light water (as in neutrosophic logic). More interestingly, his EQPET/TSC (\textit{tetrahedra symmetric condensate}) model, Takahashi can predict a new potential called STTBA (\textit{sudden-tall thin barrier} \textit{approximate}) which includes negative potential (reverse potential) and differs from Coulomb potential. The SC-potential, which has sinusoidal form, can be viewed as a generalization of Takahashi's TSC/STTBA potential. [Preview Abstract] |
|
K1.00090: ``Force Field" for Plasma Confinement Carlos Ordonez Theoretical research associated with producing an electromagnetic field referred to as a ``force field" is reported. A force field is defined at present as a static electromagnetic field that has the following characteristics: (1) It has an effective range that is much smaller than the dimensions of a cloud, plasma or beam of charged particles that is confined by the field. (2) It can simultaneously reflect incident charged particles of either sign of charge. A force field could consist of a spatially periodic sequence of magnetic cusps that are electrostatically plugged using applied electrostatic potential variations similar to that found in nested Penning traps. For plasma confinement, a possible configuration consists of a sequence of coaxial ring cusps. The diameter of the ring cusps varies axially, with the smallest rings located near the axial ends of the confinement volume. Two point cusps that are coaxial with the ring cusps are located at the axial ends of the confinement volumes. A current-carrying wire placed along the axis of symmetry could be used to produce a minimum-B configuration. In the work reported, a theoretical understanding is developed of the single-particle reflection properties of a force field that confines a non-drifting, isotropic plasma. [Preview Abstract] |
|
K1.00091: Charged Particle Interactions with a Static Electromagnetic ``Force Field" Jose Pacheco, Duncan Weathers, Carlos Ordonez Experimental research associated with producing an electromagnetic field referred to as a ``force field" is reported. A force field is defined at present as a short-range static electromagnetic field that can simultaneously reflect incident charged particles of either sign of charge. The charged particles can originate from a cloud, plasma or beam. A force field consisting of a spatially periodic sequence of magnetic cusps is investigated, where the magnetic cusps are electrostatically plugged using applied electrostatic potential variations similar to those found in nested Penning traps. Such a configuration could in principle be utilized to trap an effectively unmagnetized or minimum-B configuration plasma. The aim of the work reported is to understand the plasma-particle reflection properties of a planar force field created with straight, parallel line cusps. Initial experimental results are presented. [Preview Abstract] |
|
K1.00092: Energy Transfer Between Antiprotons and Leptons Within a Strong Magnetic Field Jose Correa, Jonathan Wurtele, Carlos Ordonez Some experiments conducted at the CERN Antiproton Decelerator are aimed at creating and confining antihydrogen. In many of the experiments, energetic antiprotons are cooled by collisions with electrons within a strong magnetic field. The cold antiprotons are subsequently made to interact with positrons under a strong magnetic field leading to some recombination. In the work to be reported, an analytical model for strongly magnetized collisions is developed and applied to investigate the energy loss of antiprotons interacting with cold and warm leptons under a strong magnetic field. In this model, the strong magnetization constrains the momentum transfer to one dimension, which is parallel to the magnetic field. Thus, collisional energy transfer is dominated by short-range collisions. The result is remarkably different from the unmagnetized case. The theoretical expectations are compared with prior and new computer simulations. The agreement found reveals that the model captures important features of the interaction of electrical charges of disparate masses such as antiprotons and leptons within a strong magnetic field. [Preview Abstract] |
|
K1.00093: Isothermal Expansion of a Solid-Particle-Entrained Gas and Plasma-Based Energy Conversion Eric Lessmann, Matthew Traum, Duncan Weathers, Carlos Ordonez Experimental and theoretical research is reported on the expansion of a two-phase fluid consisting of a mixture of compressed gas and solid particles. Experimental temperature measurements indicate that the expansion is describable as isothermal for the conditions studied. During the expansion, the energy of the compressed gas is converted into kinetic energy of the solid particles. The solid particles travel at a subsonic speed, serve as a heat exchange medium, and are recycled. In the experiment, the gas-solid two-phase fluid travels through a nozzle during the isothermal expansion. Conversion of the energy of a compressed gas has been demonstrated experimentally using a turbine to convert the kinetic energy of the solid particles into other forms. A second method is also being studied for converting the kinetic energy of the solid particles after the gas expansion. The second method, which would replace the turbine, would convert the kinetic energy of the solid particles into electrical energy by charging the solid particles (e.g., by passing them through an electron plasma or by reflection off one plate of a capacitor). The charged solid particles would then carry a current across a change in electric potential inertially (without collisions with a wall) and then be discharged (e.g., by passing them through an ion plasma or by reflection off one plate of a second capacitor). [Preview Abstract] |
|
K1.00094: Nanostructure Control of P3HT:PCBM Bulk Hetero-junction Polymer Solar Cells J. Seok, E. Gann, C.M. Balik, H. Ade, B. Ocko, X. Lu, H. Hlaing Highly regioregular Poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are a widely used model system for Bulk hetero-junction (BHJ) solar cells. For optimized P3HT:PCBM BHJ solar cells, not only is a small domain size on the order to the exciton diffusion length ($\sim $10nm) required, but the orientation of P3HT crystallites should be optimized as well. Small domains result in effective charge separation and minimize charge recombination at the interface between P3HT and PCBM. Additionally, face-on crystalline orientation of P3HT in which the $\pi -\pi $ stacking direction is parallel to the electric field enhances the hole charge carrier mobility. We are presenting a new strategy to achieve somewhat increased face-on P3HT crystalline orientation and smaller domain size in P3HT/PCBM BHJ solar cells than what is readily achievable with thermal annealing alone. This improved nanostructure control is achieved by in-situ polymerization of 2,5-dibromothiophene present in the thin films after short vapor annealing. Improvements in power conversion efficiency of approx. 30{\%} relative to thermal annealing alone were achieved. [Preview Abstract] |
|
K1.00095: First-Principles Studies on Lattice Dynamical Properties of Zn$_4$Sb$_3$ Compounds Yi Zhang, Changfeng Chen, Jihui Yang The origin of extremely low lattice thermal conductivity in Zn$_4$Sb$_3$ compound has attracted great interests but remains not fully understood due to its complex crystal structure. We have performed extensive first-principles calculations on the lattice vibration modes and thermodynamics of Zn$_4$Sb$_3$ based on its experimental crystal structure. The low frequency modes and structural inhomogeneity that could be responsible for the low thermal conductivity have been discussed. [Preview Abstract] |
|
K1.00096: Impact of impurities on the electronic structures of thermoelectric material Mg$_{2}$Si Ka Xiong, Sabina Sobhanni, Rahul Gupta, Weichao Wang, Bruce Gnade, Kyeongjae Cho Thermoelectric (TE) materials have attracted a lot of attention because of its capability of converting heat into electricity or vice versa. In this work, we investigate the effects of dopants in Mg$_{2}$Si, which is a promising TE material candidate. We calculate the electronic structures and stability of various dopants (Al, In, P, As, Sb, Bi, Ag, Cu, Zn, and Cd) in Mg$_{2}$Si with different charge states, using density functional theory (DFT) method with HSE functional which gives accurate band gap prediction. This DFT study helps us to gain insights on the defect states of these dopants in Mg$_{2}$Si and the mechanisms which cause the modulation of the Mg$_{2}$Si TE efficiency. [Preview Abstract] |
|
K1.00097: Neutron Scattering Measurements of Temperature-Dependent Phonon Spectra in Thermoelectric Materials PbTe and (Ag,Sb)Te$_{2}$ Jie Ma, Olivier Delaire, Brian Sales, Karol Marty, Douglas Abernathy, Matthew Stone, Georg Ehlers The thermoelectric materials PbTe and (Ag,Sb)Te$_{2}$, which both crystallize in the rocksalt structure, have attracted much attention due to their high \textit{zT} values. Prior theoretical and experimental studies have investigated the phonon dispersions of PbTe, and the importance of the electron-phonon and phonon-phonon couplings has been recognized. However, phonons have not been investigated in details in (Ag,Sb)Te$_{2}$. Also, little is known about the phonon linewidths, which directly correlate with the lattice thermal conductivity. In order to better understand the microscopic origins of the lattice thermal conductivity, time-of-flight and triple-axis inelastic neutron scattering measurements were performed as a function of temperature in both compounds. The results of phonon linewidths and their systematic dependence on temperature are presented, providing a direct measurement of the contribution of phonons to the total thermal conductivity. [Preview Abstract] |
|
K1.00098: Gd$_{116}$Co$_{49}$Sn$_{118}$: A Complex Intermetallic Phonon-Glass/Electron-Crystal Devin Schmitt, Neel Haldolaarachchige, Yimin Xiong, Rongying Jin, David Young, Julia Chan State-of-the art thermoelectric devices today operate at very low efficiencies and are expensive to produce. However, the growing need for alternate energy sources based on novel technologies has brought thermoelectrics to the forefront of applied materials research. Thermoelectrics could have a significant impact in this area, if their performance is significantly enhanced to a figure of merit (\textit{ZT}) above 1.5. Our research focuses on the growth and structure-property relationships of intermetallics, specifically crystal structures with large lattice parameters that contain heavy atoms. These materials may be good thermoelectric candidates due to their potentially low lattice thermal conductivities and enhanced Seebeck values resulting from polar intermetallic properties. We have recently grown Gd$_{116}$Co$_{49}$Sn$_{118}$ (\textit{Fm-3m}, $a \quad \cong $ 30.2 {\AA}), a compound related to the Dy$_{117}$Co$_{57}$Sn$_{112}$ structure type. Physical property measurements indicate that this is an ambipolar semiconductor with an exceptionally low lattice thermal conductivity ($\kappa _{l} \quad \cong $ 0.5 W/m-K). The observed phonon-glass/electron-crystal properties make Gd$_{116}$Co$_{49}$Sn$_{118}$ and its analogues potential thermoelectric candidates. [Preview Abstract] |
|
K1.00099: Bipolar Membranes for Acid Base Flow Batteries Mitchell Anthamatten, Supacharee Roddecha, Jacob Jorne, Anna Coughlan Rechargeable batteries can provide grid-scale electricity storage to match power generation with consumption and promote renewable energy sources. Flow batteries offer modular and flexible design, low cost per kWh and high efficiencies. A novel flow battery concept will be presented based on acid-base neutralization where protons (H+) and hydroxyl (OH-) ions react electrochemically to produce water. The large free energy of this highly reversible reaction can be stored chemically, and, upon discharge, can be harvested as usable electricity. The acid-base flow battery concept avoids the use of a sluggish oxygen electrode and utilizes the highly reversible hydrogen electrode, thus eliminating the need for expensive noble metal catalysts. The proposed flow battery is a hybrid of a battery and a fuel cell---hydrogen gas storing chemical energy is produced at one electrode and is immediately consumed at the other electrode. The two electrodes are exposed to low and high pH solutions, and these solutions are separated by a hybrid membrane containing a hybrid cation and anion exchange membrane (CEM/AEM). Membrane design will be discussed, along with ion-transport data for synthesized membranes. [Preview Abstract] |
|
K1.00100: ATOMIC, MOLECULAR AND OPTICAL (AMO) PHYSICS |
|
K1.00101: Universal contact of strongly interacting Fermi gases Mark DelloStritto, Theja De Silva We study strongly interacting two component Fermi gas near a Feshbach resonance. By using a ground state energy functional constructed based on asymptotic limits and Monte Carlo calculations, we calculate the contact, structure factor, and collective oscillation frequencies in the BCS-BEC crossover region. The calculated contact and structure factor show excellent agreement with recent experiments. We show that the upper bounds of the collective modes have universal form in the sense that they depend only on the contact and the homogenous energy. In other words, the collective modes of the Fermi atoms trapped near Feshbach resonance can be calculated without the explicit knowledge of trapping potential. [Preview Abstract] |
|
K1.00102: Spin-charge separation in one-dimensional fermion systems beyond Luttinger liquid theory Thomas Schmidt, Adilet Imambekov, Leonid Glazman We develop a nonperturbative zero-temperature theory for the dynamic response functions of interacting one-dimensional spin-1/2 fermions. In contrast to the conventional Luttinger liquid theory, we take into account the nonlinearity of the fermion dispersion exactly. We calculate the power-law singularities of the spectral function and the charge- and spin-density structure factors for arbitrary momenta and interaction strengths. The exponents characterizing the singularities are functions of momenta and differ significantly from the predictions of the linear Luttinger liquid theory. We generalize the notion of the spin-charge separation to the nonlinear spectrum. This generalization leads to phenomenological relations between threshold exponents and the threshold energy. [Preview Abstract] |
|
K1.00103: Control the spin coherence of a spin-1 Bose-Einstein Condensate with dynamical decoupling approach Boyuan Ning, Jun Zhuang, Wenxian Zhang, J.Q. You The coherence of spinor Bose-Einstein condensates (BECs) is determined by the dynamically unstable collective modes. Recently, Uhrig Dynamical Decoupling (UDD), a sequence containing $n$ $\pi$-pulses, has been applied to eliminate the decoherence of a qubit in the spin-boson (SB) model up to the order of $\mathcal {O}$$(t^{n+1})$ and proved to be a universal method. Stimulated by its promising power, we conjecture whether the UDD sequence could also preserve the coherence of a spinor BEC by modulating the spin exchange interaction through optical Feshbach resonance. In this work, we theoretically analyze the effect of UDD, periodic DD (PDD) and concatenated DD (CDD) to maintain the coherence of a $^{87}$Rb spin-1 BEC and a scalar BEC. Our numerical results show that the CDD, as $n$ increases, suppresses the decoherence more than the other two DD sequences in both the spinor and the scalar BECs. However, it is interesting that all three sequences only remove the decoherence up to the same order $\mathcal {O}$$(t)$. We further carry out analytical works for the scalar BEC, which confirms our numerical results that UDD, compared to the case of SB model, is not as superior as expected at coherence control in BECs. [Preview Abstract] |
|
K1.00104: Bosonic matter inside a periodic array of tubes P. Salas, F.J. Sevilla, M. Fortes, M.A. Solis We report the Bose-Einstein Condensation critical temperature, internal energy and specific heat per particle of an ideal boson gas in periodically trapping channels. These are simulated by two perpendicular external Kronig-Penney delta potentials applied on the $x$-$y$ plane and allowing the particles to move freely in the remaining direction. We obtain the Bose-Einstein condensation critical temperature of the system as a function of the separation between deltas and as a function of their intensity which models the penetrability of the tube walls. It is shown that $T_{c}$ decreases monotonically, from the 3D ideal boson gas $T_{0}$ for vanishing delta strenght, down to $0$ as the intensity grows to infinity while keeping the channel's cross section constant. The quotient $T_{c}/T_{0}$ as a function of the width of the tubes starts at $1$, reaches a minimum value that depends on the permeability and returns to $1$ as the widths vary from infinity to $0$. We observe that the specific heat as a function of the temperature is modified by the tubular structure, showing a set of maxima and minima for different values of permeability of the walls and widths of the tubes. In particular, when half the wave-length of the boson gas is the same as the tubes' square cross section, the system clearly exhibits the trapping effect due to the tubes. In this case the specific heat has a minimum very similar to that of the one- dimensional case. [Preview Abstract] |
|
K1.00105: Specific heat of bosons in periodical bilayers O.A. Rodriguez, P. Salas, M.A. Solis We report the specific heat at constant volume of an ideal boson gas inside a periodical bilayer structure modeled with a generalized Kronig-Penney (KP) delta potential in the $z$-direction while the particles are free in the other two directions. The generalized KP potential has two different strength delta potentials by unit cell, and they are separated $\beta a,$ where $a$ is the unit cell length and $0\leq \beta \leq 1$. After calculating the energy band structure we use it to obtain the Bose-Einstein condensation critical temperature besides the chemical potential, the internal energy and the specific heat, as functions of the temperature, for different values of the parameters $a$, $\beta$ and the delta strengths. For any parameter set we observe a Bose-Einstein condensation at a lower temperature than that of an infinite ideal Bose gas in the thermodynamic limit and with the same particle density. From the specific heat we distinguish at least four characteristic lengths. They are associated to the thermal wave length values at: the BEC critical temperature where the specific heat shows a peak and a discontinuity in their derivative; two minima of the specific heat where the thermal wave lengths are equal to two times the plane separations $\beta a$ and ($a - \beta a$); and about 0.7 times the minimum plane separation, where the specific heat behavior returns to that of an ideal Bose gas. Also the delta strength effects on the specific heat are discussed. [Preview Abstract] |
|
K1.00106: Probing and Manipulating Fermi Gases Using Classical Impurities Lei Jiang, Leslie O. Baksmaty, Han Pu, Hui Hu, Yan Chen Impurities can be used as probes to detect material properties and to understand quantum phenomena. Here we study the effect of a single classical impurity in ultracold s-wave Fermi superfluids. We use T-matrix and B-dG method to study both 1D and 3D cases to mean-field level. A magnetic impurity can induce a mid-gap bound state located inside the pairing gap. In addition, magnetic impurity can locally induce population imbalance in the system, potentially providing a method to realize FFLO-like state in a controlled way. We further extend the 1D impurity case to strong correlated region using DMRG. We also propose a modified RF spectroscopy to measure the local density of states, as a cold-atom analog of STM. [Preview Abstract] |
|
K1.00107: Generating sodium Bose-Einstein condensates in hybrid magnetic quadrupole and optical traps Zongkai Tian, Jie Jiang, Jared Austin, John Jepson, Yingmei Liu We present the design and construction of a novel apparatus to rapidly and simply generate $^{23}$Na Bose-Einstein condensates in hybrid magnetic and optical traps. Sodium atoms are collected in a magnetic-optical trap, captured in a magnetic quadrupole trap, and then cooled through forced radio-frequency evaporation. To avoid Majorana spin-flip losses at the center of the magnetic quadrupole trap, the cold dense atomic cloud is transferred to a crossed red-detuned optical dipole trap. By reducing the optical trap depth, sodium Bose-Einstein condensates are generated from forced evaporation and rethermalization in the crossed optical trap. This hybrid approach combines the advantages of both magnetic quadrupole and optical traps. [Preview Abstract] |
|
K1.00108: Construction and Implementation of a Low-Cost Rubidium Magneto-Optical Trap Judith Olson A low-cost magneto-optical trap (MOT) for ultra-cold atoms is a wonderful tool for undergraduate research and teaching laboratories that highlights many topics in modern physics. We researched and created such a MOT using two external-cavity diode lasers, two laser locking systems, optics, magnetic coils, and Rubidium vapor cells. At our undergraduate institution, we chose a combination of equipment that we fabricated ourselves together with some purchased items as an optimum balance between cost and building time. However, an emphasis was placed upon self-construction of components, such as machining the laser cavities and constructing the majority of the circuitry within the institution. The total cost of our MOT was about \$25,000. We were successfully able to trap more than 10 million Rubidium atoms in 1 cubic centimeter. Such a MOT is a feasible addition to any undergraduate course of study. The theory of operation and construction methods of our MOT will be presented along with our first measurement results. [Preview Abstract] |
|
K1.00109: Ultracold Realization of AntiFerromagenteic Order Uttam Shrestha We investigate numerically the experimental feasibility of observing the antiferromagnetic (AF) order in the bosonic mixtures of rubidium ($^{87}$Rb) and potassium ($^{41}$K) in a two-dimensional optical lattice with external trapping potential. Within the mean-field approximation we have found the ground states which, for a specific range of parameters such as inter-species interactions and lattice height, interpolate from phase separation to the AF order. For the moderate lattice heights the coexistence of the Mott and AF phase is possible for rubidium atoms while the potassium atoms remain superfluid with overlapped AF phase. In our view there has not been any study on AF order in two-component systems when one component remains in the superfluid phase while the other is in the Mott phase. Therefore, this observation may provide a novel regime for studying quantum magnetism in ultracold systems. [Preview Abstract] |
|
K1.00110: FFLO phase on an optical lattice: a quantum Monte Carlo study Chia-Chen Chang, Shiwei Zhang Recent experimental progress in cold Fermi gases has demonstrated the possibility of realizing exotic quantum phases in optical lattices. One example is the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state arising from pairing across the Fermi surfaces in a spin-imbalanced system with attractive interaction. We study ground state magnetic properties in 2D and 3D repulsive Hubbard models at intermediate interaction strengths by means of a highly accurate auxiliary-field quantum Monte Carlo method [1] coupled with Twist-averaged boundary conditions. The sign problem is controlled by a generalized constrained path approximation. It is found that the ground state shows incommensurate spin density wave order with periodic spatial modulation when the model is slightly doped away from $n=1$. We present our results in 2D [2] and 3D, and discuss their implications, through a particle-hole transformation, on the FFLO phase on an optical lattice of spin-imbalanced fermions with an attractive interaction. This work is supported by ARO. Reference: [1] Chia-Chen Chang and Shiwei Zhang, Phys. Rev. B 78, 165101 (2008) [2] Chia-Chen Chang and Shiwei Zhang, Phys. Rev. Lett. 104, 116402 (2010). [Preview Abstract] |
|
K1.00111: Progress toward realization of antiferromagnetic ordering of cold atoms in an optical lattice P.M. Duarte, R. Hart, T.L. Yang, J.M. Hitchcock, T.A. Corcovilos, R.G. Hulet We present progress toward the observation of antiferromagnetic (AFM) ordering of fermionic atoms in an optical lattice using Bragg scattering of light. We first laser cool $^{6}$Li atoms using the $2S_{1/2}\rightarrow 2P_{3/2}$ transition and then further cool using the $2S_{1/2}\rightarrow 3P_{3/2}$ transition to T $\sim$ 65 $\mu$K, leading to enhanced loading into a far detuned optical dipole trap. After forced evaporative cooling, an incoherent spin mixture of the two lowest magnetic sublevels of the ground state is adiabatically loaded into a 3D optical lattice. By adjusting the $s$-wave scattering length and the depth of the lattice, we tune the interaction and hopping terms of the Hubbard Hamiltonian. Bragg scattering of light from the lattice planes can be used to detect sample ordering such as in the Mott insulator state. At low temperatures and weak interactions, a phase transition to AFM ordering of the two spin states is predicted to occur. The increased symmetry of the AFM state allows for Bragg scattering of light from the ordered spin planes, $\pm$(${\scriptstyle{^1\!/_2}\,{^1\!/_2}\,{^1\!/_2}}$), and hence unambiguous detection of the AFM state. We present our progress in detecting the Mott insulator and AFM states. [Preview Abstract] |
|
K1.00112: A Qauntum Theory of Ultracold Atoms in Spatially Inhomogenoues Optical Lattices Dagim Tilahun, Byounghak Lee Ultracold atoms in optical lattices undergo a quantum phase transition from a superfluid to a Mott insulator as the potential depth is increased. But the interpretations of most cold atoms experiments are complicated by the fact that the experimental systems are inhomogeneous, for example due to the harmonic trapping potential that is always present. Or the focus of the study itself could be what causes the non-uniformity, such as disorder. Here We apply a theory developed by one of the authors and a collaborator to these inhomogeneous systems to discuss their ground state and elementary excitations. [Preview Abstract] |
|
K1.00113: Geometric Unitary Gates in Cold Atom Ensembles on an Atom Chip Yicong Zheng, Todd Brun We propose a feasible scheme to achieve quantum computation based on geometric manipulation of ensembles of atoms, and analyze it for neutral rubidium atoms magnetically trapped in planoconcave microcavities on an atom chip. The geometric operations are accomplished by optical excitation of a single atom into a Rydberg state in a constant electric field. Strong dipole-dipole interactions and incident lasers drive the dark state of the atom ensembles to undergo some specified cyclic evolutions that realize a universal set of quantum gates. Such geometric manipulation turns out naturally to protect the qubits from the errors induced by non-uniform laser illumination as well as cavity loss. The gate performance and decoherence processes are analyzed by numerical simulation. [Preview Abstract] |
|
K1.00114: A closed-cycle dilution refrigerator with free-space and fiber optical access for quantum optomechanics experiments at 25mK Simon Groeblacher, Witlef Wieczorek, Peter Christ, Matthias Buehler, Doreen Wernicke, Jens Hoehne, Markus Aspelmeyer We report on the operation of a closed-cycle dilution refrigerator for quantum optomechanics experiments at 25mK. The dilution fridge is accessible both via free-space as well as fiber coupling, allowing us to perform a variety of optical experiments at low temperatures. It is designed to vibrationally isolate the experiment allowing for stable operation of a high-finesse optical cavity. This enables us to perform cavity-optomechanics experiments at ultra-low temperatures. [Preview Abstract] |
|
K1.00115: Correlation energy of a homogeneous dipolar Fermi gas Bo Liu, Lan Yin We study the normal state of a 3-D homogeneous dipolar Fermi gas beyond the Hartree-Fock approximation. The correlation energy is found of the same order as the Fock energy, unusually strong for a Fermi-liquid system. As a result, the critical density of mechanical collapse is smaller than that in the Hartree-Fock approximation. An new energy functional including the correlation energy is constructed to describe inhomogeneous cases, and its properties are explored. [Preview Abstract] |
|
K1.00116: Quantum Phases of Fermionic Cold Atoms Through Pairing and Dissociation Nicolas Lopez, Shan-Wen Tsai, E. Timmermans, Chi-Yong Lin Cold atom experiments have realized molecule creation consisting of paired fermions and dissociation of weakly bound molecules into correlated fermions by tuning of the interactions with external fields [1,2]. We study many-body correlations in such system where molecules are weakly bound and therefore pairs of fermionic atoms convert into and dissociate from the bound molecule state. This exchange mediates a long-range interaction between the fermions. We consider a simple many-body Hamiltonian that includes the destruction of fermionic atom pairs to form single bosonic molecules and vice versa [3]. We employ a functional renormalization-group approach to search for instabilities from the disordered quantum liquid phase that may arise from a boson mediated fermion-fermion interaction. We calculate the renormalized frequency-dependent fermion interactions vertices and renormalized molecular binding energy. \\[4pt] [1] M. Greiner, C. A. Regal, and D. S. Jin, Nature {\bf 426}, 537 (2003).\\[0pt] [2] M. Greiner, C. A. Regal, J. T. Stewart, and D. S. Jin, Phys. Rev. Lett. {\bf 94}, 110401 (2005).\\[0pt] [3] E. Timmermans, K. Furuya, P. W. Milonni, and A. K. Kerman, Phys. Lett. A {\bf 285}, 228 (2001). [Preview Abstract] |
|
K1.00117: Influence of Non-Linear Interactions on the Propagation of Electromagnetic Fields in Moving Many-Electron Atomic Systems Verne Jacobs Reduced-density-matrix descriptions are developed for the propagation of electromagnetic fields in moving many-electron atomic systems, taking into account the center-of-mass motions, atomic collision processes, and applied magnetic fields. The time-domain (equation-of-motion) and the frequency-domain (resolvent- operator) formulations are developed in a unified manner. A semiclassical perturbative treatment of the electromagnetic interaction is employed to derive compact Liouville- space operator expressions for the general n'th-order non-linear macroscopic electromagnetic-response tensors. Coherent atomic excitations and the full tetradic- matrix form of the collision-radiative self-energy operator in the Markov approximation are taken into account. [Preview Abstract] |
|
K1.00118: Analysis of two simultaneous EITs in a four-level atomic system in a W-scheme using a dressed-state representation Cristian Bahrim A four-level atomic system in a W-scheme is used for slowing down \textit{simultaneously }two circularly polarized optical fields using a linearly polarized coupling field. Our four-level atomic system is composed by the ${ }^1S_0 $ ground state and three Zeeman levels of the ${ }^1P_1 $ excited state of any alkali-metal atom introduced in a weak magnetic field. When the coupling field is stronger than both probe fields, the electromagnetic induced transparency (EIT) is observed in the coherences associated to the two probes, while the coherence associated to the coupling field shows opacity. We calculate the quantum coherences from the steady-state solutions of the density matrix master equation, in which we neglect the collisional dephasing (we consider ultra-cold atoms), but we include the radiative decays from each Zeeman state to the ground state. The coupling mechanism between the atomic states and the optical fields in our W-system and the evolution of the EIT features with the intensity of the coupling field is done using an intuitive dressed state representation. We also analyze the transit time from the normal dispersive region to the EIT region: when a weak probe field is used, the transit time is the shortest and the width of the Autler-Townes doublet equals the lifetime of the excited atomic state which experiences EIT, but it increases rapidly as the intensity of the probe field increase. [Preview Abstract] |
|
K1.00119: Infrared Spectrum of the Astrophysical Molecule SiC$_{5}$ T.H. Le, W.R.M. Graham An infrared spectrum of SiC$_{5}$, one of many Si-C molecular species expected to play roles in the atmospheres of late carbon stars and in the interstellar medium, has been observed for the first time. The Fourier transform infrared spectrum (FTIR) was recorded for SiC$_{5}$ produced by trapping, in solid Ar, the products of the Nd:YAG laser ablation of a sintered, silicon-carbon rod enriched with $^{13}$C. Based on excellent agreement between measured frequencies of $^{13}$C and $^{29,30}$Si isotopomers and the predictions of DFT (density functional theory) B3LYP/cc-pVDZ calculations, the linear geometry of SiC$_{5}$ has been confirmed and the \textit{$\nu $}$_{4}$(\textit{$\sigma $}$_{u})$ asymmetric stretching fundamental of SiC$_{5}$ has been identified at 936.9 $\pm $ 0.2 cm $^{-1}$. [Preview Abstract] |
|
K1.00120: Vibrational Spectroscopy and Structures of Novel Metal-Carbon Species of Astrophysical Interest Micheline Bejjani, William Graham, Magnus Rittby This study on metal-carbon molecules is part of an ongoing investigation of the structures and vibrational frequencies of small metal carbide clusters using Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT). These studies are motivated by the potential presence of small metal carbide molecules in astrophysical environments. Binary carbon compounds containing silicon and sulfur, including SiC$_{2}$, SiC$_{3}$, and SC$_{3}$, have been observed in interstellar space and circumstellar shells. In addition several metal-containing molecules, such as MgCN and MgNC have also been detected. Hence, metal carbides have been suggested as possible interstellar molecules although a lack of information on their spectral properties may so far have prevented their detection. Recent studies by this laboratory on the infrared spectroscopy of matrix-isolated metal tricarbide clusters, such as fanlike TiC$_{3}$ and ScC$_{3}$, linear CrC$_{3}$ and CoC$_{3}$ and floppy NiC$_{3}$Ni have begun to provide some of this information. Here, we report the structures and vibrational spectra of MnC$_{3}$, ZnC$_{3}$ and MgC$_{3}^{-}$. [Preview Abstract] |
|
K1.00121: The two-dimensional and three dimensional confinement of the hydrogen molecular ion, inside ellipses and spheroids, respectively Martin Molinar, German Campoy-G\"uere\~na The Schr\"{o}dinger equation for the confinement of the hydrogen molecular ion in the Born -- Oppenheimer is solved. The molecule is confined by rigid and non-rigid ellipses and spheroids. The energies for the ground state and the first excited states are determined. [Preview Abstract] |
|
K1.00122: Variational wave function approach to quantum quenches in bosonic systems Federico Becca, Giuseppe Carleo, Stefano Baroni Recent experiments with ultracold atomic gases have opened the possibility for studying non-equilibrium quantum dynamics of many-body systems. In particular, the high degree of tunability allows one to rapidly change system parameters and observe the subsequent quantum evolution. We present a new variational approach to deal with time-dependent problems where quantum quenches of the microscopic parameters induce a highly non-trivial dynamics. We show to what extent a generalization of the Jastrow wave function may accomplish this task, even for two-dimensional models, where standard Lanczos or density-matrix renormalization group methods are highly limited. Examples for interacting hard-core and soft-core bosons are shown. The generalization to fermionic models is also discussed. [Preview Abstract] |
|
K1.00123: Phase diagram of a population-imbalanced attractive Fermi gas in the 1D-3D crossover regime Satyan Bhongale, Leslie Baksmaty, Lei Jiang, Han Pu Phase diagram of a population imbalanced attractive Fermi gas in the 1D-3D dimensional crossover regime is obtained via deriving a multi-channel inter-atomic scattering pseudopotential. Such a phase diagram has strong implications for the observation of FFLO superfluidity within trapped fermions. Recent experiment with ultra-cold Li6 have mapped the phase diagram for 1D attractive fermions [Nature 467, 567 (2010)], however the superfluid property is yet to be confirmed. While the signature of FFLO in 1D is predicted to coincide with micro-phase separated domains, the feasibility of direct experimental identification of the domain walls remains questionable due to strong fluctuations. On the other hand, in 3D, fluctuations may be neglected, but the FFLO corresponds to just a tiny sliver of the phase diagram. Moreover, the topology of the phase diagram is drastically different in the two extreme dimensional limits. We show how the 1D and 3D dimensional limits are connected and indicate the possible new physics in the crossover regime. [Preview Abstract] |
|
K1.00124: Controllable optical switch using a Bose-Einstein condensate in an optical cavity Shuai Yang, M. Al-Amri, J\"{o}rg Evers, M. Suhail Zubairy The optical bistability of an ultra cold atomic ensemble located in a small volume ultra-high finesse optical cavity is investigated. We find that the transverse pumping field can be used to control the bistable behavior of the intra cavity photons induced by the input pumping along the cavity axis. This phenomenon can be used as a controllable optical switch. [Preview Abstract] |
|
K1.00125: QUANTUM INFORMATION, CONCEPTS AND COMPUTATION |
|
K1.00126: Quantum Mechanics as Dualism Robert Jones I do not agree with mind-body dualism. Today the consensus view is that thought and mind is a combination of processes like memory, generalization, comparison, deduction, organization, induction, classification, feature detection, analogy, etc. performed by computational machinery. (R. Jones, Trans. of the Kansas Acad. Sci., vol. 109, \# 3/4, 2006 and www.robert-w-jones.com, philosopher, theory of thought) But I believe that quantum mechanics is a more plausible dualist theory of reality. The quantum mechanical wave function is nonphysical, it exists in a 3N space (for an N body system) not in (x,y,z,t) 4-space, and does not possess physical properties. But real physical things like energy (which do exist in our 4-space world) influence the wave function and the wave function, in its turn, influences real physical things, like where a particle can be found in 4-space. The coupling between the spirit-like wave function and things found in the real (4-space) world (like energy) is via mathematical equations like the Schrodinger equation and Born normalization. [Preview Abstract] |
|
K1.00127: Some Statistical Measures and Analytical Results of Quantum Walks under Weak Measurement and Weak Values Regime Debabrata Ghoshal, Marco Lanzagorta, Salvador Venegas-andraca Motivated by experimental results on quantum weak measurements and weak values as well as by the need to develop new insights for quantum algorithm development, we study the behavior of quantum walks under the regime of quantum weak measurements and weak values of pre- and post-selected measurements (QWWM hereinafter). In particular, we investigate the limiting position probability distribution and several statistical measures (such as standard deviation) of a QWWM on an infinite line, and compare such results with corresponding classical and quantum walks position probability distributions and statistical measures, stressing the differences provided by weak measurements and weak values with respect to results computed by using canonical observables. We start by producing a concise introduction to quantum weak values and quantum weak measurements. We then introduce definitions as well as both analytical and numerical results for a QWWM under Hadamard evolution and extend our analysis to quantum evolution ruled by general unitary operators. Moreover, we define a 2-walker QWWM on an infinite 2D lattice and explore its behavior on limiting probability distribution, standard deviation and degree of entanglement between walkers. [Preview Abstract] |
|
K1.00128: Generating Entangled States With Hybrid Parity Gates Zhi-Ming Zhang, Feng Mei, Ya-Fei Yu, Xun-Li Feng We propose a scheme for generating entangled states among different single atoms trapped in separated cavities. In our scheme, by reflecting an input coherent optical pulse from a cavity with a single trapped atom, a controlled phase-shift gate between the atom and the coherent optical pulse can be achieved. Based on this gate and homodyne detection, we construct an n-qubit parity gate and show its use for distribution of a large class of entangled states, including the GHZ states, the W states, the Dicke states, and certain sums of the Dicke states. We also show that such distribution can be performed with high success probability and high fidelity even in the presence of channel loss. [Preview Abstract] |
|
K1.00129: Optical Engineering for Quantum Computing Over the Optical Frequency Comb Moran Chen, Olivier Pfister The optical frequency comb (OFC) of a single optical parametric oscillator (OPO) has shown a spectacular, if theoretical, scalability potential as a continuous-variable one-way quantum register. Indeed, an arbitrarily large, square-grid cluster state, suitable for universal quantum computing, can in principle be generated in one fell swoop in the OPO, by use of a triply concurrent nonlinear crystal (already demonstrated) and a 15-mode pump. Here we present a precise and feasible implementation plan for this complex pump spectrum, using single-sideband, suppressed-carrier (SSB-SC) electrooptic modulation. Another requirement is the proper termination of the set of interacting entangled modes within the OFC. We show that OFC dispersion can be realistically managed, by use of microcavity OPO mirrors, so as to shift the frontier modes out of resonance and essentially annihilate their interaction. Solving these two ``optical engineering'' problems paves the way to the experimental realization of scalable cluster-state entanglement ``over the rainbow.'' [Preview Abstract] |
|
K1.00130: Implementing quantum phase gates with Ising anyons David J. Clarke, Kirill Shtengel Non-Abelian anyons of Ising type are likely to occur in a number of physical systems, including quantum Hall systems, where recent experiments support their existence. In general, non-Abelian anyons may be utilized to provide a topologically error-protected medium for quantum information processing. However, the topologically protected operations that may be obtained by braiding and measuring topological charge of Ising anyons are not computationally universal. Nevertheless they can be made universal when supplemented with a single-qubit phase gate. We propose a method of implementing arbitrary single qubit phase gates for Ising anyons by utilizing interference of auxiliary anyons around computational anyons. While this gate is not topologically protected, our estimates show that its error rate can be made lower than the threshold for error correction. The error rate for systems with neutral Ising anyons (e.g. topological insulator) is inherently lower than that for systems in which the anyons carry charge (e.g. quantum Hall systems). [Preview Abstract] |
|
K1.00131: Finding edge permutations in a graph using quantum walks Zlatko Dimcovic, Yevgeniy Kovchegov The problem of graph structure discovery is important in many fields of science. Quantum walks are expected to bring significant algorithmic improvements to quantum computing. More generally, random walks (Markov chains on graphs) can be very useful as a different approach to problems. We use a specific quantum walk to address unknown permutations in a graph. Consider two matching graphs, with unknown permutations of edges that connect them. For example: a vertex on the left is connected to a set of vertices to its right; on the far right is another vertex, connected to another set of nodes, to its left. These two sets of nodes are connected in the middle, but we do not know which left nodes connect to which right ones. We construct a quantum walk on such a graph structure that allows us to gain a surprising amount of information, or completely determine permutations, often in a single pass over the graph. We detect classes of interesting properties of our walk on such unknown graphs. Classical walks cannot resolve some cases at all, implying a formally ``infinite'' speed up. This walk is an example of use of our recent framework for building quantum walks, based on classical walks with memory. The framework contains all major known walks, while it can also build walks on structures prohibitively difficult for current techniques. [Preview Abstract] |
|
K1.00132: Decoherence in a Dynamical Quantum Phase Transition Sarah Mostame, Gernot Schaller, Ralf Schuetzhold Motivated by the similarity between adiabatic quantum algorithms and quantum phase transitions, we study the impact of decoherence on the sweep through a second-order quantum phase transition for the prototypical example of the Ising chain in a transverse field. For site-independent and site-dependent coupling strengths as well as different operator couplings, the results show that (in contrast to first-order transitions) the impact of decoherence caused by a weak coupling to a rather general environment increases with system size which might limit the scalability of the corresponding adiabatic quantum algorithm. We also propose a physical setup that can be used to simulate the quantum dynamics of the Ising model. [Preview Abstract] |
|
K1.00133: Quantum Phase Transitions in Cavity Coupled Dot systems Vijay Kasisomayajula, Onofrio Russo We investigate a Quantum Dot System, in which the transconductance, in part, is due to spin coupling, with each dot subjected to a biasing voltage. When this system is housed in a QED cavity, the cavity dot coupling alters the spin coupling of the coupled dots significantly via the Purcell Effect. In this paper we show the extent to which one can control the various coupling parameters: the inter dot coupling, the individual dots coupling with the cavity and the coupled dots coupling with the cavity as a single entity. We show that the dots coupled to each other and to the cavity, the spin transport can be controlled selectively.\footnote{http://publish.aps.org/search/field/author/Trif\_Mircea (Trif Mircea), http://publish.aps.org/search/field/author/Golovach\_Vitaly\_N (Vitaly N. Golovach), and http://publish.aps.org/search/field/author/Loss\_Daniel (Daniel Loss), Phys. Rev. B 75, 085307 (2007)} We derive the conditions for such control explicitly. Further, we discuss the Quantum phase transition effects due to the charge and spin transport through the dots.\footnote{Michal Grochol, PRB 79, 205306 2009} The electron transport through the dots, electron-electron spin interaction and the electron-photon interaction are treated using the Non-equilibrium Green's Function Formalism. [Preview Abstract] |
|
K1.00134: Efficient control of the NV center spin in diamond Zhi-Hui Wang, Domenico D'Alessandro, Viatcheslav Dobrovitski Fast and accurate control of the spin of a nitrogen-vacancy (NV) center in diamond is a key for realization of diamond-based quantum information processing. We investigate time-optimal rotation [1] of a qubit implemented with the spin of a NV center. We examine performance of the control, and show that one can achieve a gain of 25\% in rotation time compared to the broadly used rotating wave approximation. At certain values of the bias field, noticeable population accumulates on the third energy level and the fidelity of the control is degraded. We show that this is due to the transitions induced by the higher-order harmonics in the control field, which can be suppressed by frequency filtering of the control field at the expense of increased rotation time.\\[4pt] [1] U. Boscain, P. Mason, J. Math. Phys. 47, 062101 (2006). [Preview Abstract] |
|
K1.00135: Observation of $\sigma _{x}$ coupling signal in a gap-tunable flux qubit Xiaobo Zhu, Alexander Kemp, Shiro Saito, Hayato Nakano, Kouichi Semba We experimentally demonstrate the \textit{in situ} tunability of the gap of a superconducting flux qubit, which was achieved by replacing the smallest Josephson junction of the qubit with a dc-SQUID. We observe different gaps as a function of the external magnetic pre-biasing field and the local magnetic field through the dc-SQUID controlled by high-bandwidth on chip control lines. The persistent current and gap behavior agree well with the numerical simulation results. We set the sensitivity of the gap on the control lines during the sample design stage. With a tuning range of several gigahertz on a qubit dynamics timescale, we observe coherent system dynamics at the degeneracy point [1]. We measured the microwave amplitude dependence of Rabi frequency at the same resonant frequency but at different flux bias of the gap-tunable flux qubit. It showed a systematical deviation between these two set of data, which indicated we observed $\sigma _{x}$ coupling signal between the flux qubit and the microwave-line. Different from conventional $\sigma _{z}$ coupling, this $\sigma _{x}$ coupling has a remarkable merit toward realization of idea QND measurement. \\[4pt] [1] Xiaobo Zhu, Alexander Kemp, Shiro Saito, and Kouichi Semba, APPLIED PHYSICS LETTERS 97, 102503 (2010). [Preview Abstract] |
|
K1.00136: Characterization of flux-driven Josephson parametric amplifiers A. Baust, E.P. Menzel, T. Niemczyk, E. Hoffmann, M. Haeberlein, F. Deppe, A. Marx, R. Gross, E. Solano, K. Inomata, T. Yamamoto, Y. Nakamura Phase sensitive linear amplifiers receive increasing interest for applications in the field of circuit QED as they allow for the amplification of one signal quadrature without, in principle, adding noise. The flux-driven Josephson parametric amplifier characterized in this work is formed by a SQUID- terminated transmission line resonator with resonant frequency that can be varied by applying an ac magnetic flux signal through the SQUID. We have characterized two Josephson parametric amplifiers with different design parameters with respect to the center frequency and quality factor of the resonator, phase-dependent and phase-independent gains, as well as compression points and bandwidths. [Preview Abstract] |
|
K1.00137: Towards ultrastrong coupling of superconducting transmission line resonators F. Deppe, T. Weissl, E. Hoffmann, M. Haeberlein, A. Baust, E. Menzel, M. Schwarz, T. Niemczyk, A. Marx, D. Zueco, J. J. Garcia Ripoll, R. Gross Coupled superconducting transmission line resonators have potential applications in quantum information processing and fundamental quantum mechanics. Experimentally, high coupling strengths are desirable for a clear demonstration of quantum effects. We achieve coupling strengths of 10\% of the resonator frequency (ultrastrong coupling) by distributed coupling. We find that, differently from the case of point-like coupling, the normal modes are no longer arranged symmetrically with respect to the single resonator frequency. Nevertheless, a detailed theoretical analysis shows that the system can still be described by a beam splitter Hamiltonian for two effective resonators. We expect that this result will allow for straightforward experimental access to exciting effects such as thermal entanglement in our samples. [Preview Abstract] |
|
K1.00138: Observation of 0.2 ms Lifetime in a Cooper-pair Box Z. Kim, B. Suri, V. Zaretskey, S. Novikov, K. Osborn, A. Mizel, F. Wellstood, B. Palmer We have coupled a quasi-lumped element superconducting microwave resonator with a resonant frequency of 5.44 GHz to an Al/AlO$_{\mbox{x}}$/Al Cooper-pair box (CPB) charge qubit. The resonator is in turn weakly coupled to a transmission line and shows no higher resonant modes up to 20 GHz. By monitoring perturbations of the resonant frequency, we have measured the spectrum and lifetime ($T_{1}$) of the CPB at the charge degeneracy point while the CPB was detuned from the resonator by up to 3.5 GHz. The maximum $T_{1}$ of the CPB was 200 $\mu$s for $f$ = 4 to 4.5 GHz, while $T_{1}$ decreased to 4 $\mu$s around 8 GHz. Our measured $T_{1}$'s imply that the loss tangent in the AlO$_{\mbox{x}}$ junction barrier must be less than about $4\times 10^{-8}$ at 4.5 GHz, about 4 orders of magnitude less than reported in larger area Al/AlO$_{\mbox{x}}$/Al tunnel junctions. [Preview Abstract] |
|
K1.00139: ABSTRACT WITHDRAWN |
|
K1.00140: "Quantum-Computing"(Q-C) = Simple-Arithmetic Since Digits = Quanta/Bosons Via Algebraic-INVERSION 1881($<$1901-05-25) of Digits On-Average Logarithmic-Law = ONLY BEQS!!! E. I. Pi, Edward Carl-Ludwig Siegel Digits'(On Average) Newcomb(1881)-Weyl(1914)-Benford(1938) "NeWBe" Logarithmic-Law $<$P$>$ = log{\{}base=10{\}}(1 + 1/d) = log{\{}base=10{\}}([d + 1]/d) Siegel [Abs.973-60-124, AMS Nat.Mtg.(2002)] INVERSION to ONLY Bose-Einstein quantum-statistics(BEQS) d = 1/[10\^{}($<$P$>)$-1] $\sim $ 1/[exp($<$P$>)$-1]$\sim $ 1/[exp($<$w$>)$-1] $\sim $ {\{}1/[1+($<$w$>)$+...]-1] $\sim $ "1"/$<$w$>$\^{}1.000...Archimedes' Zipf-law HYPERBOLICITY ("noise" $\sim $ "generalized-susceptibility") power-spectrum INEVITABILITY with gapFUL BEC to digit d = 0, $<$P(0)$>$ = oo, GAP = [$<$P(0)$>$=oo]-[$<$P(1)$>$=0.32]=oo has deep meaning for (so called) Q-C. Identification of digits(BCE) as quanta(1901-05 ACE) because quanta are/always were digits: energy-levels: ground-state d=0, first excited-state d=1,..., with no intermediate/fractional-levels, separated by quantum: Q = (d=1)-(d=0) = 1 means (on average any/all simple arithmetic computations with digits are ab initio by definition Q-C. Example: a blank-check is a BEC of digits d=0; writing some non-zero digits d$>$0, then signing check, is quantum-excitation from d=0 to d$>$0. Thus (so called) Q-C has existed since man learned to count/manipulate hand's digits. Simple arithmetic(except for: division; factoring with remainders) is/has been from time immemorial (on average) "Q-C"!!! [Preview Abstract] |
|
K1.00141: DichotomY IdentitY: Euler-Bernoulli Numbers, Sets-Multisets, FD-BE Quantum-Statistics, 1/f$\backslash $\^{}{\{}0{\}}-1/f$\backslash $\^{}{\{}1{\}} Power-Spectra, Ellipse-Hyperbola Conic-Sections, Local-Global Extent: "Category-Semantics" G.-C. Rota, Edward Carl-Ludwig Siegel Seminal Apostol[Math.Mag.81,3,178(08);Am.Math.Month.115,9,795(08)]-Rota[Intro.Prob. Thy.(95)-p.50-55] DichotomY equivalence-class: set-theory: sets V multisets; closed V open; to Abromowitz-Stegun[Hdbk.Math.Fns.(64)]-ch.23,p.803!]: numbers/polynomials generating-functions: Euler V Bernoulli; to Siegel[Schrodinger Cent.Symp.(87); Symp.Fractals, MRS Fall Mtg.,(1989)-5-papers!] power-spectrum: 1/f$\backslash $\^{}{\{}0{\}}-White V 1/f$\backslash $\^{}{\{}1{\}}-Zipf/Pink (Archimedes) HYPERBOLICITY INEVITABILITY; to analytic-geometry Conic-Sections: Ellipse V (via Parabola) V Hyperbola; to Extent/Scale/Radius: Locality V Globality, Root-Causes/Ultimate-Origins: Dimensionality: odd-Z V (via fractal) V even-Z, to Symmetries/(Noether's-theorem connected)/Conservation-Laws Dichotomy: restored/conservation/convergence=0- V broken/non-conservation/divergence=/=0: with asymptotic-limit antipodes morphisms/ crossovers: Eureka!!!; "FUZZYICS"=''CATEGORYICS''!!! Connection to Kummer(1850) Bernoulli-numbers proof of FLT is via Siegel(CCNY;1964) $<$ (1994)[AMS Joint Mtg. (2002)-Abs.973-60-124] short succinct physics proof: FLT = Least-Action Principle!!! [Preview Abstract] |
|
K1.00142: NON-Shor Factorization Via BEQS BEC: Watkins Number-Theory "Pure"-Mathematics U With Statistical-Physics; Benford Log-Law Inversion to ONLY BEQS digit d=0 BEC!!! M. Lyons, Edward Carl-Ludwig Siegel Weiss-Page-Holthaus[Physica A,341,586(04); \underline {http://arxiv.org/abs/cond-mat/0403295}] number-FACTORIZATION VIA BEQS BEC VS.(?) Shor-algorithm, strongly-supporting Watkins' [\underline {www.secamlocal.ex.ac.uk/people/staff/mrwatkin/}] Intersection of number-theory "pure"-maths WITH (Statistical)-Physics, as Siegel[AMS Joint.Mtg.(02)-Abs.973-60-124] Benford logarithmic-law algebraic-INVERSION to ONLY BEQS with d=0 digit $<$P(d=0)$>$=oo gapFUL BEC!!! Siegel Riemann-hypothesis proof via Rayleigh[Phil.Trans.CLXI(1870)]-Polya[Math.Ann.(21)]-[Random-Walks {\&} Electric-Nets., MAA(81)]-"Anderson"[PRL(58)]-localization-Siegel[Symp.Fractals,MRS Fall Mtg.(89)-5-papers!!!] FUZZYICS=CATEGORYICS: [LOCALITY]--MORPHISM/CROSSOVER/ AUTMATHCAT/DIM-CAT/ ANTONYM--$>$(GLOBALITY) FUNCTOR/SYNONYM/ concomitance to "noise"$<$=/Fluct.-Dissip. theorem/ FUNCTOR/SYNONYM/ equivalence/proportionality to =$>$ "generalized-susceptibility" power-spectrum [FLAT/FUNCTIONLESS/WHITE]--MORPHISM/ CROSSOVER/AUTMATHCAT/DIM-CAT/ANTONYM--$>$ HYPERBOLICITY/ZIPF-law INEVITABILITY) intersection with ONLY BEQS BEC). [Preview Abstract] |
|
K1.00143: Number-Theory in Nuclear-Physics in Number-Theory: Non-Primality Factorization As Fission VS. Primality As Fusion; Composites' Islands of INstability: Feshbach-Resonances? A. Smith, Edward Carl-Ludwig Siegel Numbers: primality/indivisibility/non-factorization versus compositeness/divisibility/ factorization, often in tandem but not always, provocatively close analogy to nuclear-physics: (2 + 1)=(fusion)=3; (3+1)=(fission)=4[=2 x 2]; (4+1)=(fusion)=5; (5 +1)=(fission)=6[=2 x 3]; (6 + 1)=(fusion)=7; (7+1)=(fission)=8[= 2 x 4 = 2 x 2 x 2]; (8 + 1) =(non: fission nor fusion)= 9[=3 x 3]; then ONLY composites' Islands of fusion-INstability: 8, 9, 10; then 14, 15, 16, {\ldots} Could inter-digit Feshbach-resonances exist??? Possible applications to: quantum-information/ computing non-Shore factorization, millennium-problem Riemann-hypotheses proof as Goodkin BEC intersection with graph-theory "short-cut" method: Rayleigh(1870)-Polya(1922)-"Anderson"(1958)-localization, Goldbach-conjecture, financial auditing/accounting as quantum-statistical-physics; {\ldots}abound!!! Watkins [\underline {www.secamlocal.ex.ac.uk/people/staff/mrwatkin/}] "Number-Theory in Physics" many interconnections: "pure"-maths number-theory to physics including Siegel [AMS Joint Mtg.(2002)-Abs.{\#} 973-60-124] inversion of statistics on-average digits' Newcomb(1881)-Weyl(14-16)-Benford(38)-law to reveal both the quantum and BEQS (digits = bosons = digits:"spinEless-boZos"). 1881 $<$ 1885 $<$ 1901 $<$ 1905 $<$ 1925 $<$ 1927, altering quantum-theory history!!! [Preview Abstract] |
|
K1.00144: Physics Proofs of Four Millennium-Problems(MP) via CATEGORY-SEMANTICS(C-S)/F=C Aristotle SQUARE-of-OPPOSITION(SoO) DEduction-LOGIC DichotomY London Clay, Edward Carl-Ludwig Siegel Siegel-Baez Cognitive-Category-Semantics"(C-C-S) tabular list-format matrix truth-table analytics SoO jargonial-obfuscation elimination query WHAT? yields four "pure"-maths MP "Feet of Clay!!!" proofs: (1) Siegel [AMS Natl.Mtg.(02)-Abs.973-03-126: (CCNY;\underline {6}4)!!!$<<<$(\underline {9}4;Wiles)] Fermat's: Last-Thm. = Least-Action Ppl.; (2) P=/=NP TRIVIAL simple Euclid geometry/dimensions: NO computer anything"Feet of Clay!!!"; (3) Birch-Swinnerton-Dyer conjecture; (4) Riemann-hypotheses via COMBO.: Siegel[AMS Natl.Mtg.(02)-Abs.973-60-124] digits log-law inversion to ONLY BEQS with ONLY zero-digit BEC, AND Rayleigh[1\underline {8}70;graph-thy."short-CUT method"[Doyle-Snell, \underline {Random-Walks {\&} Electric-Nets},MAA(81)]-"Anderson"[(58)] critical-strip C-localization!!! SoO DichotomY ("V") IdentitY: {\#}s:( Euler v Bernoulli) = (Sets v Multisets) = Quantum-Statistics(FD v BE) = Power-Spectra(1/f\^{}(0) v 1/f\^{}(1)) = Conic-Sections(Ellipse v Hyperbola) = Extent(Locality v Globality);Siegel[(89)] (so MIScalled) "complexity" as UTTER-SIMPLICITY(!!!) v COMPLICATEDNESS MEASURE(S) definition. [Preview Abstract] |
|
K1.00145: P =/=NP Category-Semantics(C-S) TRIVIAL Proof: EUCLID!!! [(So Miscalled) Computational-Complexity(CC) Jargonial-Obfuscation(J-O); (Which???) MillenniumED-ProblemED(M-P): NO CC, CS; Feet of Clay!!!] Edward Carl-Ludwig Siegel P=/=NP M-P proof is by C-S J-O elimination! C-S P=(?)=NP MEANS (Deterministic).(P-C)=(?)=(NON-Deterministic).(P-C)=(NP). C-S P=(?)=NP MEANS (Deterministic).(P-C)=(?)=(Non-Deterministic).(P-C) i.e. D.(P)=(?)= N.(P). For inclusion(equality) vs. EXclusion(INequality), IRrelevant(P) simply cancels! (Equally any other CC IF both sides identical). Crucial question left (D)=(?)=(N-D), i.e. D =(?)= N. Algorithmics: Deterministic (D) serial vs. NON-deterministic (N) NON-serial, branch fork forms a triangle, its vertices a plane. Menger Dimension-Theory: Dimensionality: D serial is one-dimensional, dim(D) = 1 (definition), VS. dim(N= NON-serial) =/= one-dimensional; dim(N) = [2(branching; fork; triangle; plane)+ E(probabilistic)] $>$ 2 [Sipser [Intro. Thy. Comp.(1997)-p. 49; Fig. 1.15!!!]]. Hence (Euclid[$\sim $ -350 BCE]) simple formative geometry, dim(D) = 1 =/= dim(N) = [2(branching)+ E(probabilistic)] $>$ 2, Left-to-Right INclusion VS. Right-to-Left EXclusion. Hence P =/= NP!!! QED, i.e. D =/= N, i.e. dim(D) = 1 =/= dim(N) $>$ 2 by first millennium BCE, before CS J-O of CC!!! Harder doable C-S J-O analysis proofs: any combinations of DIS-similar CCs: LHS and D with low CC and/or RHS and N-D=N with high CC! [Preview Abstract] |
|
K1.00146: Algorithmic-Reducibility = Renormalization-Group Fixed-Points; "Noise"-Induced Phase-Transitions (NITs) to Accelerate Algorithmics ("NIT-Picking") Replacing CRUTCHES!!!: Gauss Modular/Clock-Arithmetic Congruences = Signal X Noise PRODUCTS. . J. Siegel, Edward Carl-Ludwig Siegel Cook-Levin computational-"complexity"(C-C) algorithmic-equivalence reduction-theorem reducibility equivalence to renormalization-(semi)-group phase-transitions critical-phenomena statistical-physics universality-classes fixed-points, is exploited with Gauss modular/clock-arithmetic/model congruences = signal X noise PRODUCT reinterpretation. Siegel-Baez FUZZYICS=CATEGORYICS(SON of ``TRIZ''): Category-Semantics(C-S) tabular list-format truth-table matrix analytics predicts and implements "noise"-induced phase-transitions (NITs) to accelerate versus to decelerate Harel [Algorithmics(1987)]-Sipser[Intro. Theory Computation(1997) algorithmic C-C: "NIT-picking" to optimize optimization-problems optimally(OOPO). Versus iso-"noise" power-spectrum quantitative-only amplitude/magnitude-only variation stochastic-resonance, this "NIT-picking" is "noise" power-spectrum QUALitative-type variation via quantitative critical-exponents variation. Computer-"science" algorithmic C-C models: Turing-machine, finite-state-models/automata, are identified as early-days once-workable but NOW ONLY LIMITING CRUTCHES IMPEDING latter-days new-insights!!! [Preview Abstract] |
|
K1.00147: MAGNETISM (EXPERIMENT, THEORY, APPLICATIONS) |
|
K1.00148: Impurity effects in excitonic insulators Jian Li, Ningning Hao Both nonmagnetic and magnetic impurity effects in spin singlet and triplet excitonic insulators were investigated. The bound state energies caused by single impurity were given. The different compositions of the bound states can be used to detect the symmetry of the excitonic insulators. In finite concentration problems, nonmagnetic impurities showed same pair-breaking effect in singlet and triplet excitonic insulators while magnetic impurities showed weaker pair-breaking effect in triplet excitonic insulators than in singlet ones. The pair-breaking effects suppressed the ferromagnetic range via doping and gave a natural explaination for experimental results. [Preview Abstract] |
|
K1.00149: Origins of Asymmetric Magnetization Reversal in Exchange Biased Multilayers Yang Liu, Shuoguo Wang, Yang Li, Ning Chen, Shuai Liu, Minghua Li, Guanghua Yu Novel asymmetric magnetization reversal behaviors (ARBs) as well as positive exchange bias (EB) are observed by using the alternating gradient force magnetometer (AGM) in both Co/FeMn bilayer with an oblique out-of-plane exchange anisotropy and the Co/FeMn bilayer in which Co layer has a quite heavy thickness. There are two different ARBs, arised from the ferromagnetic and the antiferromagnetic layer respectively under the perpendicular magnetization. Our results show that two intrinsic origins of the ARBs (i.e. the competing anisotropy and the inhomogeneity of the magnetic structure) coexist. Both of them are indispensable for the development of the ARBs in our Co/FeMn multilayers. [Preview Abstract] |
|
K1.00150: Magnetic properties of $FeCl_3$ investigated by ${}^{57}Fe$ NMR Byeongki Kang, Soonchil Lee $FeCl_3$ crystallizes in a hexagonal layered structure and has a spiral antiferromagnetic phase below $T_N=8.8 K$, where the spins are spirally ordered with $2\pi/15$ period along [140] direction. It is reported that the magnetic phase changes to an order with two sublattices above $1.5 T$ and there is a spin- flop transition above $4.0 T$. We observed ${}^{57}Fe$ ferromagnetic nuclear magnetic resonance(NMR) signal for $FeCl_3 $ for the first time at low temperature. The sublattice magnetization $M(T)$ obtained from the temperature dependence of the NMR frequency is well fit by the Bloch's $T^2$ law for antiferromagnets. The spectral change with external field provided a microscopic evidence for the spin-flop transition. The transition was not abrupt but progressive with increasing field. [Preview Abstract] |
|
K1.00151: Investigations of Exchange and Magnetic Anisotropic Interactions of Magnetic Ions in Antiferromagnetic Materials Alexander Bazhan Investigations of exchange and magnetic anisotropic interactions of magnetic ions, which determine antiferromagnetic orderings in materials, used in HTS, are of interest due to investigations of transformations of antiferromagnetic orderings, when additional two dimensional systems of correlated electrons, holes carriers are introduced. Discussions of states, which can appear before HTS, are of interest in such investigations. In experimental investigations of, determined by exchange and magnetic anisotropic interactions, magnetic phase transitions, investigations of separate components of samples magnetic moments, which determine orientations of samples magnetic moments, are useful. Investigations of, determined by orientations of ordered magnetic moments, magnetic phase transitions in antiferromagnetic materials and states with weak ferromagnetism at selected orientations of ordered magnetic moments in antiferromagnetic materials using vector vibrating sample magnetometer with horizontal magnetic field, up to 90kOe, and liquid helium temperatures, which can investigate separately magnetic field dependencies of three perpendicular components of samples magnetic moments, demonstrate possibilities of such magnetometers in investigations of exchange and magnetic anisotropic interactions of magnetic ions. [Preview Abstract] |
|
K1.00152: Kinetic properties of small one-dimensional Ising magnetic Vladimir Udodov, Dmitriy Spirin Within the framework of a generalized Ising model, a one-dimensional magnetic of a finite length with free ends is considered. The correlation length critical exponent $\nu $ and kinetic critical exponent z of the magnet is calculated taking into account the next nearest neighbor interactions and the external field. Of special interest are non-equilibrium processes taking place within the critical temperature interval, which are characterized critical exponent y and dynamic critical index $z$. Due to significant difficulties encountered in the experimental investigations (e.g., measurement of $z)$, a natural solution to this complex problem would be modeling of those non-eqilibrium processes. This work addresses non-equilibrium processes in one-dimensional magnetics. Using the Monte Carlo method, an equilibrium critical exponent of the correlation length $\nu $ and the dynamic critical index $z$ are calculated for a finite-size magnetic. [Preview Abstract] |
|
K1.00153: On the critical behaviour of two-dimensional liquid crystals Ana I. Fari\~nas-S\'anchez, Robert Botet, Bertrand Berche, Ricardo Paredes The Lebwohl-Lasher (LL) model is the traditional model used to describe the nematic-isotropic transition of real liquid crystals. In this paper, we develop a numerical study of the temperature behaviour and of finite-size scaling of the two-dimensional (2D) LL-model. We discuss two possible scenarios. In the first one, the 2D LL-model presents a phase transition similar to the topological transition appearing in the 2D XY-model. In the second one, the 2D LL-model does not exhibit any critical transition, but its low temperature behaviour is rather characterized by a crossover from a disordered phase to an ordered phase at zero temperature. We realize and discuss various comparisons with the 2D XY-model and the 2D Heisenberg model. Having added finite-size scaling behaviour of the order parameter and conformal mapping of order parameter profile to previous studies, we analyze the critical scaling of the probability distribution function; hyperscaling relations and stiffness order parameter and conclude that the second scenario (no critical transition) is the most plausible. [Preview Abstract] |
|
K1.00154: Re-entrant spin glass state in (Ce$_{1-x}$Tb$_{x})$Fe$_{2}$ compounds A. Haldar, K.G. Suresh, A.K. Nigam Doped CeFe$_{2}$ compounds are well known for their unique features like first order magneto-structural transition, metastability, supercooling/superheating effects, phase co-existence, glassiness etc. 4$f$ band magnetism and the antiferromagnetic ground state as a consequence of this are the interesting features of this system Though doping at the Fe site has been studied extensively, the effect of rare earth (R) substitution at the Ce site is not investigated in detail. We have recently shown that Er substitution causes a spin glass state below its ordering temperature. In this paper, we show that a similar re-entrant spin glass (RSG) phase can be achieved with Tb substitution as well. Characteristic experimental evidences, like large thermo-magnetic irreversibility and strong frequency dependence of ac-susceptibility have been observed. Spin freezing temperature has been found to obey critical slowing down mechanism with relaxation time of the order of 10$^{-6 }$s. The relaxation behavior is also investigated using time variation of dc magnetization. Theoretical fitting of the relaxation data suggests that that the RSG state is made of clusters and not of atomic moments. The RSG state is attributed to the random substitution of Tb in the nearly nonmagnetic Ce sublattice and the modulation of the R-Fe exchange. [Preview Abstract] |
|
K1.00155: The first-Order phase transition in $\beta$-MnO$_{2}$ studied by $^{55}$Mn Nuclear Magnetic Resonance Changsoo Kim, Euna Jo, Soonchil Lee $\beta$-MnO$_{2}$ has a conductivity due to negative charge carriers generated from slight off-stoichiometry of oxygens. We obtained 55Mn antiferromagnetic nuclear magnetic resonance (NMR) signal for $\beta$-MnO$_{2}$ at low temperature for the first time. The resonance frequency of the main peak centered at 254 MHz is nearly unchanged from 4.2 K to 130 K though it is known that the magnetic phase changes near 94 K from the antiferromagnetic state to the paramagnetic state. This suggests that the magnetic phase transition is a first order transition and the mixed phases coexist both below and above the phase transition temperature. Side peaks were found at 161 MHz, 181 MHz and 297 MHz. Through annealing $\beta$-MnO$_ {2}$, which generates oxygen defects, we investigated whether these peaks originate from manganese ions with their valence other than 4+. However, the NMR spectra of the annealed $\beta$- MnO$_{2}$ showed no difference in side peaks. [Preview Abstract] |
|
K1.00156: $^{55}$Mn NMR for Antiferromagnetic $\alpha$-Mn$_{2}$O$_{3}$ Euna Jo, Changsoo Kim, Soonchil Lee The zero-field $^{55}$Mn NMR spectrum for antiferromagnetic $\alpha$-Mn$_{2}$O$_{3}$ was measured at low temperatures. Manganese sesquioxide (Mn$_{2}$O$_{3}$) is used in combustion catalysis, a method of reducing the emissions of organic compounds and nitrous oxide from waste gas, as an environmentally - friendly and inexpensive catalyzer instead of Pt and Pd. The magnetic moment estimated from the resonance frequency was 2.6$\mu_{B}$ per Mn$^{3+}$ ion. The temperature dependence of the sublattice magnetization fits not Bloch's $T^{2}$ law well but the exponential form applicable because there is an initial energy gap in the dispersion relation of the spin wave. From the fitting, an energy gap of 1.82 meV and an anisotropy energy of 0.22 meV were obtained. The spin-spin relaxation rate was measured as a function of the frequency and the Suhl-Nakamura interaction is suppressed by this energy gap. [Preview Abstract] |
|
K1.00157: Hysteresis in weak ferromagnets Ya. B. Bazaliy, L.T. Tsymbal, G.N. Kakazei, S.V. Vasiliev Magnetic hysteresis is studied in the orthoferrites ErFeO3 and TmFeO3 using the single crystal samples of millimeter dimensions. It is shown that in both materials one observes a temperature transition manifesting itself through the temperature hysteresis of the magnetic moment and a peculiar temperature evolution of the field hysteresis loop shapes near this transition. Experiments rule out the hypothesis that the ordering of the orthoferrite's rare earth magnetic moments plays an important role in these phenomena. The hysteresis curves can be explained by a few-domain magnetic state of the samples that results from the weak ferromagnetism of the orthoferrites. The phenomenon is generic for weak ferromagnets with temperature dependent magnetization. A large characteristic magnetic length makes the behavior of the relatively big samples analogous to that observed in the nano-size samples of strong ferromagnets. [Preview Abstract] |
|
K1.00158: Measurements of charge localization effects in uranium and plutonium intermetallic compounds from $L_{\rm III}$ X-ray absorption spectroscopy Yu Jiang, C.H. Booth, E.D. Bauer, J.N. Mitchell, P.H. Tobash, J.D. Thompson, J.L. Sarrao, M.A. Wall, P.G. Allen, D. Nordlund At the heart of the complex behavior of 5$f$-electrons in uranium and plutonium is the variable localization of the 5$f$ orbital. Plutonium, in particular, can behave like a localized lanthanide system or a delocalized transition-metal system, depending on its coordination environment. This behavior gives rise to a variety of novel physical properties in U and Pu compounds: unexpected magnetic susceptibilities, non-Fermi-liquid behavior, superconductivity, etc. To understand the dual nature of U and Pu 5$f$ orbitals, we report measurements of the actinide $L_{\rm III}$-edge X-ray absorption spectra, including high-resolution partial fluorescence yield measurements, for a wide variety of intermetallics, including $\alpha$-U, UCoGa$_5$, UCd$_{11}$, $\alpha-$ and $\delta-$Pu, PuCoGa$_5$, and PuCoIn$_5$. A systematic shift of the $L_{\rm III}$-edge energy is observed, and is correlated to the Sommerfeld coefficient from heat capacity measurements. Based on these results, we argue that this type of experiment is a direct measure of the degree of 5$f$ orbital localization for U and Pu. [Preview Abstract] |
|
K1.00159: Anisotropic magnetic behavior of single crystalline CeGe Sudesh Dhar, Pranab Kumar Das, Neeraj Kumar, Arumugam Thamizhavel, Ruta Kulkarni We report the anisotropic magnetic properties of a Czochralski grown single crystal of CeGe, which crystallizes in the orthorhombic structure with the space group Pnma ({\#}63). The compound orders antiferromagnetically at TN = 10.9 K, in agreement with the value reported previously on a polycrystalline sample. A metamagnetic transition at $\sim $ 6.5 T followed by saturation at higher fields is observed along [010], the easy axis of magnetization. The heat capacity data confirm the bulk nature of magnetic ordering with a peak of nearly 13 J/mol K at 10.9 K. The peak decreases in height and shifts to lower temperatures in applied magnetic field, consistent with the antiferromagnetic ordering of Ce ions. Subtraction of phonon heat capacity, as measured for LaGe, reveals a broad hump around 30 K, suggesting the existence of low lying crystal electric field levels, which is well reproduced by two doublets located at 45 and 152 K, respectively. The electrical resistivity shows normal metallic behavior indicating the absence of Kondo interaction. At TN the resistivity measured along the three principal directions shows an upturn which is tentatively attributed to the gaps opened in the antiferromagnetic state. A magnetic phase diagram has been constructed based on the magnetization data. [Preview Abstract] |
|
K1.00160: Spin-polarization and transmission properties in heterostructures with magnetic nano elements Armen Kocharian, Avag Sahakyan, Ruzan Movsesyan The problem of electron resonant and non-resonant scatterings on two magnetized barriers is studied in the one-dimension. The transfer-matrix is built up to exactly calculate the coefficient of the electron transmittance through the system of two magnetic barriers with non-collinear magnetizations. The polarization of the transmitted electron wave for resonance and non-resonance transmittances is calculated [Kocharian, et al, JMMM 322, L42, 2010]. The transmittance coefficient and spin polarization can be drastically enhanced and controlled by the angle between the barrier magnetizations. Our result for spin transmission is analogous to Malus's law for passing light polarization through crossed polarizers. This provides efficient control of spin polarization via the applied magnetic field which is an apparent manifestation of the spin- valve effect. The strong dependence of magnetoconductance on the non-colinearity angle in two magnetized barriers resembles the corresponding effects in noncollinear spintronics for a number of other magnetic multilayer heterostructured systems and layered magnetic nanostructures. [Preview Abstract] |
|
K1.00161: Nb doped TiN as a superconducting electrode for spin polarization measurements of oxides Dipanjan Mazumdar, Manjit Pathak, Xing Zhong, Vijay Kartik, Arunava Gupta, Patrick Leclair Spin Polarized tunneling (SPT) measurements are an unambiguous way of measuring the interface spin polarization (SP) of oxide thin films and interfaces. SPT uses a superconducting electrode as a spin detector, probing within $\sim $1 meV of the Fermi level. However the commonly used superconductor, namely Al, is not suitable for oxides due to its strong chemical affinity for oxygen. Nitrides like TiN and NbN alleviates this problem. Here we propose the use of Nb doped TiN. The critical temperature (T$_{c})$ and magnetic field (H$_{c})$ for TiN are too low for practical SPT measurements. While NbN has a higher T$_{c}$ and H$_{c}$, its high spin-orbit scattering rate makes it less ideal for SPT [1]. TiNbN should provide a sufficiently high H$_{c}$ and T$_{c}$ while maintaining a sufficiently low spin-orbit scattering rate for high-resolution SPT measurements. We present measurements of known high SP oxides ( LaSrMnO$_{3})$ and of all-oxide spin-filter devices (LSMO/STO/NFO). \\[4pt] [1] Hyunsoo Yang \textit{et al}. Appl. Phys. Lett. \textbf{88}, 182501 (2006) [Preview Abstract] |
|
K1.00162: DIFFUSIVE-Magnetoresistance(DMR) Proton(PMR)/Hydrogen-ion WATER: PRE-"Fert"/"Grunberg" GMR[and CMR]: Quo-Vadis ``Honesty''???: PLAGIARISM!!! \newline Albart Fart, Peter Gruntbug, Edward Siegel Proton/Hydrogen-ion \underline {\textit{Diffusive}}-Magnetoresistance(DMR) of Siegel[APS March-Mtgs.(70s)] based upon Siegel[Int'l. Conf. Mag.-Alloys and Oxides("ICMAO"), The Technion(77); J. Mag. Mag. Mtls. 7, 312(78)] FIRST experimental-discovery of GMR and FIRST theoretical prediction of CMR[ibid. 7, 338 (78)], facilitates NEW water production in global-warming exacerbated dry arid/semi-arid regions: Only HYDROGEN is/can be "FLYING-WATER"!!! (aka "chemical-rain-in-pipelines"). EMET/TRUTH-in-the-``SEANCES'', would-be "Sciences": C. Perelman-Corredoira [Against the Tide(07)] featuring Martin-Bradshaw ["Healing the SHAME That BINDS You"(80s)] systemic sociological-dysfunctionality(S-D), and Grigory Perelman's HEROIC ETHICS (refusal of both pure-maths Poincare-conjecture proof 2007 Fields-medal and 2010 Clay-Institute so-called/media-hyped/P.Red/spin-doctored millennium-prize million-dollar would-be award, militates as well in the current "SEANCE" of physics/maths politics/media-hype/P.R /spin-doctoring VS. Siegel FIRST experimental GMR a never-acknowledged full decade PRE-"Fert"(88) /"Grunberg(89)" ``Phales-GroPE''/Thompson-CSF/ KFZ-JEWlich 2007 physics Wolf/Japan/Nobel-prizes!!! [Preview Abstract] |
|
K1.00163: Investigation of spin torque driven magnetization reversal in elliptical elements Angelique Montgomery, Claudia K.A. Mewes, Tim Mewes Spin transfer torque [1, 2] can be utilized to switch the magnetization in small ferromagnetic elements, which can be used to implement a magnetic random access memory [3]. One crucial parameter for spin torque switching is the critical current required to achieve switching. To investigate spin transfer torque we simulate the magnetization dynamics using our Matlab based micromagnetic code (M$^{3})$, which uses a fast Fourier transform method to evaluate the longrange magnetostatic field, exchange interaction is implemented using 6, 12 or 26 neighbor methods [4] and also includes adiabatic and non-adiabatic spin torque terms. We have performed simulations using different mesh sizes to examine the influence of the cell size on the micromagnetic results. We have investigated the influence of the current density and pinned layer orientation on the magnetization dynamics and in particular on the switching time. \\[4pt] [1] J. Slonczewski, J. Mag. Mag. Mat. \textbf{159}, 1 (1996). \newline [2] L. Berger, Phys. Rev. B \textbf{54}, 9353 (1996). \newline [3] E. Chen et al., IEEE Trans. Mag. \textbf{46}, 1873-1878 (2010). \newline [4] M.J. Donahue, D.G. Porter, Physica B \textbf{343}, 177 (2004). [Preview Abstract] |
|
K1.00164: Demagnetization field distribution in paramagnetic materials Neil Baumann, Michael Mallernee, Ross Dickinson, Guoqing Wu A general method for the calculation of distribution of demagnetization field in paramagnetic materials is described, and the demagnetization field is calculated for samples with rectangular geometries. The results show high non-uniformity for the demagnetization field inside the sample depending on the sample aspect ratio and the direction of the externally applied magnetic field. Application is made to the modeling of the NMR spectra, providing good fit to the measured NMR spectra. [Preview Abstract] |
|
K1.00165: Magnetic Damping in Individual Cobalt Nanoparticles Wenchao Jiang, Felipe Tijiwa Birk, Dragomir Davidovic Magnetization precession in ferromagnets is subject to damping by means of coupling between the magnetization and the environment. In a ferromagnetic metallic particle, the damping changes in a fundamental way when the electron-in-a-box level spacing becomes larger than the magnetization precession energy. Damping has crucial significance in magnetic storage technology, so understanding its size dependence is important for the miniaturization of electronics. Here, we present an electron tunneling technique to study damping in single Cobalt nanoparticles tunnel coupled to non-magnetic leads. Injecting a tunnel current into the particle raises its magnon temperature and induces magnetization dynamics. Tunnel currents as low as a few pA are able to excite or even reverse the particle's magnetization. Using the magnetic switching field as a magnon thermometer, we obtain very low values ($10^{-8}$) for the dimensionless damping parameter, $\alpha$, indicating weak dissipative coupling to the environment. [Preview Abstract] |
|
K1.00166: Thin Film Study of YFeO3 Deposited Via Pulsed Laser Deposition for Use in Spintronic Applications Adam Hinckley, Ram Gupta, Yesappa Kolekar, Kartik Ghosh, Pawan Kahol Recently, rare-earth orthoferrites have received much attention. Their propensity for multiferroic capabilities could play a key role in the fabrication of an efficient spintronic system. Such materials as BiFeO3 and CeFeO3 have already shown promise for uses in microphotonics as well as acting as spin valves, where YFeO3 has been shown to exhibit weak ferromagnetic tendencies in bulk. However, research conducted on the magnetic and electrical properties of YFeO3 thin films are sparse and in need of further investigation. Hence we have developed bulk YFeO3 for the purpose of investigating these thin film properties. Films will be grown via KrF Pulsed Laser Deposition on LaAlO3 substrates due to their similar lattice constant values and characterized via X-Ray Diffraction, Hall Effect Analysis and SQUID Magnetometer examinations. Previous SQUID results from the bulk material display an inverted hysteresis loop, indicating the existence of differing magnetic phases in bulk. Our goal is to examine the effects from thin film construction on these magnetic phases and examine whether thin films of YFeO3 exhibit a coupling between magnetic and electrical phases. This work is supported by National Science Foundation (Award Number DMR- 0907037). [Preview Abstract] |
|
K1.00167: Quntum beat generated by an acoustic wave in single-molecule magnets Gwang-Hee Kim The Spin oscillation is studied for the case where a standing acoustic wave is delivered to two level states in single-molecule magnets. In order to obtain such states, we first saturate the sample in strong negative magnetic field and increase the field until it reaches zero. Maintaining zero field, we begin to apply the standing acousitc wave to the sample and see the change of the magnetization between the ground state and the excited state. Taking $\langle S_z \rangle$ averaged over the wavelength of the sound where $\langle S_z \rangle$ is the expectation value of the projection of the spin onto the easy anisotropy axis, we present the analytic form of $\langle S_z \rangle$ at $\hbar \omega=\Delta$ where $\omega$ is the frequency of sound and $\Delta$ the energy gap between two states. In addition, we find the optimal condition for quatnum beat strucuture and discuss the possibility of the future experiment. [Preview Abstract] |
|
K1.00168: Unusual Magnetic Behaviors with Large Anisotropy and 1/3 Magnetization Plateau in the CoV$_{2}$O$_{6}$ S.-Y. Park, T.-H. Jang, B.-G. Park, K.-P. Hong, Y.-H. Jeong The pseudo-one dimensional brannerite type CoV$_{2}$O$_{6}$ has been studied by magnetization measurement, heat capacity and neutron powder diffraction between 300 and 1.5K. CoV$_{2}$O$_{6} $ crystallizes in two modifications; a low-temperature $\gamma$- form of triclinic structure and high-temperature $\alpha$-form of monoclinic structure. $\alpha$-CoV$_{2}$O$_{6}$ of monoclinic structure shows a large magnetic anisotropy and an antiferromagnetic transition at T$_{N}$=14K. Furthermore, the magnetization measurement up to 9T shows 1/3 magnetization plateau below 10K and saturated magnetic moment ~4.5$\mu_{B} $/Co$^{2+}$, which is much larger than the spin-only value of 3.0$\mu_{B}$/Co$^{2+}$ for the full moments of Co$^{2+}$ ions. On the contrary, $\gamma$-CoV$_{2}$O$_{6}$ of triclinic structure shows saturated magnetic moment 3.0$\mu_{B}$/Co$^{2+} $ with antiferromagnetic trantion at T$_{N}$=6.2K. We discuss the different magnetic behaviors of the $\alpha$- and $\gamma$- phase of CoV$_{2}$O$_{6}$. [Preview Abstract] |
|
K1.00169: Magnetic Carbon Nanotubes Tethered with Maghemite Nanoparticles Il Tae Kim, Grady Nunnery, Karl Jacob, Justin Schwartz, Xiaotao Liu, Rina Tannenbaum We describe a novel, facile method for the synthesis of magnetic carbon nanotubes (m-CNTs) decorated with monodisperse $\gamma $-Fe$_{2}$O$_{3}$ magnetic (maghemite) nanoparticles and their aligned feature in a magnetic field. The tethering of the nanoparticles was achieved by the initial activation of the surface of the CNTs with carboxylic acid groups, followed by the attachment of the $\gamma $-Fe$_{2}$O$_{3}$ nanoparticles via a modified sol-gel process. Sodium dodecylbenzene sulfonate (NaDDBS) was introduced into the suspension to prevent the formation of an iron oxide 3D network. Various characterization methods were used to confirm the formation of well-defined maghemite nanoparticles. The tethered nanoparticles imparted magnetic characteristics to the CNTs, which became superparamagnetic. The m-CNTs were oriented parallel to the direction of a magnetic field. This has the potential of enhancing various properties, e.g. mechanical and electrical properties, in composite materials. [Preview Abstract] |
|
K1.00170: The spin -1 anisotropic Heisenberg antiferromagnet on a square lattice at low temperatures Antonio Pires In the last years the quantum two dimensional spin 1/2 Heisenberg antiferromangnet has been extensively studied. However, new physical features, such as quantum phase transitions, due to additional terms, as for instance single ion anisotropy, are possible when S = 1. Here we study the low temperature behavior of the quantum spin-1 Heisenberg antiferromagnet with exchange and single site anisotropies on the square lattice. The properties of the model change drastically as the single ions anisotropy D varies from very small to very large values. A quantum phase transition takes place at a critical value of D. Two techniques are used to study the model. In the low D region we use a self consistent harmonic approximation. For D above the critical value a bond operator formalism is used. We present the phase diagram for the model. [Preview Abstract] |
|
K1.00171: Critical theory of the topological quantum phase transition in the AKLT--SZH chain Hong-Chen Jiang, Stephan Rachel, Zheng-Yu Weng, Shou-Cheng Zhang, Zhenghan Wang We systematically study the phase diagram of $S=2$ spin chain by means of density-matrix renormalization group and exact diagonalization. We find two gapped phases which are topologically distinct: the AKLT phase is characterized by $S=1$ edge spins while the SZH phase by $S=3/2$ edge spins. Except from a multicritical point where a direct topological quantum phase transition occurs, we identify a dimer phase between both gapped phases. The whole phase boundary between dimer and SZH phases, including the multicritical point, is a critical line with central charge $c=5/2$. Finally, we propose and confirm that this line corresponds to $\rm SO(5)_1$ Wess--Zumino--Witten conformal field theory. [Preview Abstract] |
|
K1.00172: Deuterated vs Normal Hydrogen Magnetism of M (Mn,Co) Dichloride Monohydrate, and Crystal Structure S. Pagola, K.T. Trowell, K.C. Havas, Z.D. Reed, D.G. Chan, G.C. DeFotis Presented here are susceptibility data for fully deuterated forms of the title materials, and comparison with normal hydrogen forms. Also shown is the first structure determination for any monohydrate compound, for the Mn system with the simplest magnetic behavior to analyze. Interesting similarities and contrasts appear relative to normal hydrogen analogs. For the Co system the location of an enhanced susceptibility maximum, and its magnitude, match very well those of the normal hydrogen form. The deuterated Mn material shows a similar very broad susceptibility maximum as normal material, implying low-dimensional (probably d=1) magnetism, and with indication of a transition somewhat below T(max), presumably due to weak interchain interactions. But, the location of the maximum is at significantly lower temperature than in normal material, and the size is larger; both findings suggest a weaker intrachain interaction. Yet, the apparent transition, near 2.17 K, differs hardly at all in location from that in the normal material. The crystal structure determination for the normal Mn system provides the first evidence of a structural reason for the low dimensional magnetism observed, in that somewhat isolated magnetic chains are apparent. [Preview Abstract] |
|
K1.00173: Effects of Magnetic Correlation of Localized Spins in Graphene Yuriy Semenov, John Zavada, Kostyantyn Borysenko, Ki Wook Kim Prior analysis of the indirect exchange interaction between localized spins (LS) in graphene reveals an alternate sign depending on whether two LS belong to the same graphene sublattice or not. Prompted by these findings, we explored the role of the carrier-impurity exchange interaction in formation of magnetic phase states in graphene with vacancies and modification in graphene-based composite structures. Analysis of free energy F shows the anti-ferromagnetic (AF) ordering with partial compensation of the magnetizations M$_A$ and M$_B$ in two graphene sublattices. The difference M$_A$-M$_B$ is caused by difference of the number of LS randomly distributed over the sublattices A and B. This effect of weak ferromagnetism becomes significant in multi-domain structure, provided a mean domain size is around 2 $\mu$m; it can explain the available experimental results. The proximity to ferromagnetic dielectric layers in a sandwich configuration results in an indirect magnetic interaction that can be expressed in terms of exchange bias field. The latter strongly depends on vacancy concentration x and even can reverse the direction of exchange bias field with x increasing. At the temperature of AF ordering the minimum of F corresponds to a tilt of M$_A$ and M$_B$ and even a collapse of the AF vector. [Preview Abstract] |
|
K1.00174: Magnetic impurities in spin-spiral multiferroic materials Trinanjan Datta We investigate the effect of magnetic impurities in the magnetic-spiral-induced multiferroic phases using an effective multiferroic Hamiltonian. We model the impurities as a two- level system and consider the regimes when the impurity spins relax both slowly and fast. Using realistic material parameters we study the effect of impurities on ferroelectricity for varying impurity strength. We find that when the impurity strength is weak the electric polarization is not affected. However as the impurity strength is increased the amplitude of the host spin components is reduced and the ferroelectricity suppressed. We also discuss the role of impurities on a realistic multiferroic spin Hamiltonian for the rare-earth- metal Mn perovskites. [Preview Abstract] |
|
K1.00175: Magnetism of Co/Mn/Ni Dichloride Dihydrate G.C. DeFotis, A.S. Hampton, J.M. Pothen, T.J. Wallin, E.A. Welshhans, K.C. Havas, K.T. Trowell Many unusual kinds of behavior have appeared in well selected binary magnetic mixtures. It is also of interest to explore suitable ternary mixtures. Surveyed here are magnetic susceptibility and magnetization measurements for a range of compositions of the title system. This is only the second ternary insulating mixed magnet to be examined with systematic composition variation. Intrachain exchange is ferromagnetic in the Co and Ni components and antiferromagnetic in the Mn (chemical/structural metal-dichloride...infinite chains). Interchain interactions are comparable in size to intrachain, and antiferromagnetic in each component. Competing interactions occur in mixtures, as well as different kinds of spin anisotropy. Remarkable variety appears in the form of susceptibility vs temperature plots for different compositions, reflecting effects of random mixing. Different compositions display a susceptibility maximum located differently from any pure component's, or two maxima, or no maximum. Magnetization vs field isotherms also display contrasting behavior for different compositions, and varying degrees of hysteresis. [Preview Abstract] |
|
K1.00176: Coercivity, Anisotropy, and Relaxation in Nanocrystalline Gd$_{1-x}$Fe$_{x}$ Alloys with x $\le$ 0.3 P.M. Shand, A.L. Meyer, M.W. Streicher, V.J. Litwinowicz, J.E. Shield, D.L. Leslie-Pelecky We have performed extensive dc and ac magnetization measurements on nanocrystalline Gd$_{1-x}$Fe$_{x}$(x $\le$ 0.3) alloys at temperatures below the ferromagnetic Curie temperature. The coercivity for all $x$ values generally increases with decreasing temperature. The temperature variation is similar to that of unalloyed Gd; however, the size of the coercivity at a given temperature varies with $x$ in a non-monotonic fashion. The anisotropy as a function of temperature was extracted by applying the random anisotropy model to magnetization vs. field data. The variation of the anisotropy with temperature was very similar to the behavior of the coercivity, indicating that anisotropy is the dominant mechanism that drives the coercivity. The imaginary part of the ac susceptibility exhibited a peak at low temperatures. The temperature $T_{p}$ at which the peak occurred shifts with frequency in a manner analogous to a cluster glass. For a given frequency, $T_{p}$ increases with $x$. These phenomena can be explained in terms of the microscopic structure of the Gd$_{1-x}$Fe$_{x}$ alloys, which consists of nanoscale grains of Gd surrounded by disordered grain-boundary regions where the Fe atoms preferentially locate. [Preview Abstract] |
|
K1.00177: Suppressing local hot spots due to eddy currents in magnetic coil systems Zhen Yao, Aaron Shojinaga, Yong Wu, Shmaryu Shvartsman, Timothy Eagan, Thomas Chmielewski, Robert Brown A particular goal in magnetic field applications is to avoid eddy current heating in coils and shields. It is important, in MRI, for example, to avoid hot spots near the patient to be imaged as well as in the vicinity of soldering joints. We develop effective analytical formulas for the eddy current behavior of sources close to surrounding conductors, we verify these via numerical simulations, and we make successful comparisons to corresponding experimental temperature distributions. Optimized patterns of incisions made in the conductors are discovered for addressing particularly troublesome heating locations. The criteria include the need to minimize the number and length of the cuts. Theory and experiment are in agreement on the efficacy of this method for reducing steady-state temperatures. An example of results in the practical design of commercial coils and shields is that a single cut parallel to the long edge of rectangular conductors reduces the temperatures much more than making multiple cuts parallel to the short edge. [Preview Abstract] |
|
K1.00178: Anomalous remanent magnetization dependence of exchange bias effect in Ni50Mn37In13 BaoMin Wang, Yong Liu, Lan Wang Here, we report an anomalous remanent magnetization dependence of exchange bias effect in Ni50Mn37In13 alloy. Both the value of exchange bias field and its sign can be tuned by the amplitude of remanent magnetization without changing its sign. This tunability is strongly dependent on the direction of initial magnetizing field for the hysteresis loop measurements. These results can be explained well by our recent proposal of isothermal field-induced transition from superspin glass to superferromagnetic state in Ni50Mn37In13 alloy. [Preview Abstract] |
|
K1.00179: Indirect spin-spin interaction mediated by cavity photons Guillermo Quinteiro I theoretically investigate the spin-spin indirect interaction mediated by photons, and compare the results with previous work on the indirect interaction mediated by excitons and/or polaritons in bulk semiconductor and two-dimensional cavities. The systems consist of a cavity, either 0D or 2D, containing two QDs, each one coupled to a donor impurity. The neutral QDs are excited by a cavity photon, and the resulting exciton interacts with the impurity via exchange between the electron in the donor and the electron in the exciton. In the case of a 2D cavity, where the system is optically excited by an off-resonance monochromatic laser field, I deduce an effective Ising Hamiltonian for the spin-spin interaction using a perturbation theory approach. In the case of a 0D cavity, the exact eigenvalues and eigenvectors of the complete Hamiltonian involving the donors, excitons and cavity photons were determined by numerical diagonalization. The eigenvectors and energies were then used to calculate the spin-spin correlation and an effective donor-donor Hamiltonian was deduced. The numerical calculations performed for all admissible values of the physical constants revealed that the in-plane or xy correlation is zero; thus, I concluded that the effective interaction is of the Ising type. In addition, I found that the largest effective coupling $J_{eff}$ corresponds to a situation where the excitons and the cavity photon are completely mixed, forming a polariton. [Preview Abstract] |
|
K1.00180: Characterizing Multiferroics: Analyses through X-Ray Diffraction Evan Wolfe, Harley Hart, Sheldon Blackshire, Srinivas Polisetty, Disheng Chen, Jinling Zhou, Charles Frye, Mikel Holcomb Theory and experiments support that magnetoelectric coupling (electrical control of magnetism and vice versa) can be enhanced by taking advantage of interfacial coupling between magnetic and ferroelectric films. The interface between ferroelectric PZT and ferromagnetic LSMO is a promising candidate for storage and magnetic sensing devices. For example, LSMO, when exposed to a magnetic field, will contract; while PZT when strained will produce a voltage. Combining properties, the PZT/LSMO composite can be utilized to detect magnetic fields, and also be used as an energy scavenging device. In order to maximize the coupling across this interface, proper measurements and characterizations must be taken to detail how the materials interact on the atomic level. X-ray diffraction allows us to determine thickness, composite, and strain of the samples used. By analyzing the peak shift in XRD scans along our samples we can detail the amount of strain placed on the sample, aiding in discovering of the mechanisms responsible for interfacial magnetoelectric coupling. Through analysis, we can ensure the quality of the interface, thus allowing further advances for increases in magnetic sensitivity and higher voltage output. [Preview Abstract] |
|
K1.00181: Effect of annealing on the local structure of Fe and Co in CoFeB/MgO based magnetic tunnel junction: An extended X-ray absorption fine structure study Abdul Rumaiz, Joseph Woicik, Weigang Wang, Cherno Jaye, Hassnain Jaffari, C.L Chien, Jean Jordan-Sweet, John Xiao The evolution of the local structure of Fe and Co as a function of annealing time in CoFeB/MgO/CoFeB magnetic tunnel junctions was studied using extended x-ray-absorption fine structure (EXAFS). EXAFS indicates B depletion and crystallization of the CoFeB layers within a few seconds of the post growth high temperature anneal. The decrease in first-shell Debye--Waller factor and hence the increase in structural order during annealing explains the increase in tunnel magnetoresistance observed as a result of post deposition annealing. Although the diffusion of B has also been confirmed by several other experiments, there has not been much consensus on where the B diffuses after high temperature anneal. Recent results from B Near edge x-ray absorption fine structure (NEXAFS) will also be discussed. [Preview Abstract] |
|
K1.00182: Anisotropy Energy, Spin-Atomic Vibration Interaction, and Spin-Flip Hamiltonian of a Single Atomic Spin in a Crystal Field Satoshi Kokado, Kikuo Harigaya, Akimasa Sakuma We derive the anisotropy energy $V_{\rm A}$, the spin-atomic vibration interaction $V_{\rm SA}$, and the spin-flip Hamiltonian $V_{\rm SF}$ of a single atomic spin system, ``Fe$^ {2+}$ (3d$^6$) in a crystal field of tetragonal symmetry'' [1,2]. We here apply the perturbation theory to a model with the spin- orbit interaction and the kinetic and potential energies of electrons. The model also takes into account the difference in vibration displacement between an effective nucleus and electrons, $\Delta r$. We first find conditions to enhance a coefficient $|D|$ of $V_{\rm A}$=$-|D|S_Z^2$, where $D$ is an anisotropy constant and $S_Z$ is the $Z$ component of a spin operator. Second, we show that $V_{\rm SA}$ appears for $\Delta r\ne 0$, while $V_{\rm SF}$ is present independently of $\Delta r$. Also, the magnitudes of the coefficients of $V_{\rm SA}$ can be larger than those of the conventional spin-phonon interaction depending on vibration frequency. \\[4pt] [1] S. Kokado {\it et al}., J. Phys. Soc. Jpn. {\bf 79}, 114721 (2010).\\[0pt] [2] S. Kokado {\it et al}., phys. stat. solidi (c) {\bf 7}, 2612 (2010). [Preview Abstract] |
|
K1.00183: Synthesis and Analysis of Rare-Earth Nanoparticles Gd and Nd Jose Amaral, Carmin Liang, Dulce Romero, Pei-chun Ho, Saeed Attar, Dennis Margosan We have synthesized sub-micron gadolinium particles using sodium borohydride reduction of gadolinium chloride in an inverse micelle solution of the surfactant didodecyldimethylammonium bromide (DDAB) and toluene. Gadolinium and neodymium are paramagnetic rare earth metals at room temperature and become ferromagnetic and anti-ferromagnetic below 293K and 19K, respectively. A liquid-liquid extraction using two immiscible solvents can separate the magnetic nanoparticles from unwanted by-products of the reduction. SEM images show spherical Gadolinium clusters less than one micrometer were produced. Nd nanoparticles do not synthesize using toluene and water and results using methanol and hexane are on-going. Magnetic nanoparticles can have enhanced magnetization and increased density in a finite region compared to their bulk material. Possible applications include high-density magnetic storage, high-density recording media, contrast agents to improve medical magnetic resonance imaging, and magnetic refrigeration. [Preview Abstract] |
|
K1.00184: High-temperature performance of bulk nanocomposite SmCo$_{5}$/-Fe(Co) magnets Chuanbing Rong, Narayan Poudyal, J. Ping Liu, Ying Zhang, M.J. Kramer Permanent magnetic materials capable of operating at elevated temperatures are highly required for advanced power systems. In this work, a new processing technique has been adopted to produce SmCo$_{5}$-based bulk nanocomposite magnets with high thermal stability. The processing consists of severe plastic deformation and warm compaction. The structure and high-temperature magnetic property characterizations show that the microstructure does not change with heating temperature up to 500 $^{\circ}$C which ensures effective inter-phase exchange coupling at elevated temperature. It was also found that the thermal stability of the bulk nanocomposite magnets can be significantly improved with increasing density (decreasing porosity). The room temperature energy product drops fast with heating temperature above 300 $^{\circ}$C for the magnets with 80{\%} density, and with minimum decrease for the magnets with full density. Energy product about 11.1 MGOe can be obtained at 300 $^{o\circ}$C in the fully dense isotropic bulk SmCo$_{5}$/Fe nanocomposite magnets. [Preview Abstract] |
|
K1.00185: Unusual Structure and Magnetism in MnO Nanoclusters Shreemoyee Ganguly, Mukul Kabir, Biplab Sanyal, Abhijit Mookerjee We report an unusual structural and magnetic evolution in stoichiometric MnO nanoclusters by an extensive and unbiased search through the potential energy surface within density functional theory. The $(MnO)_n$ nanoclusters adopt two-dimensional structures in size ranges in which $Mn_n$ nanoclusters are three-dimensional and regardless of the size of the nanocluster, the magnetic coupling is found to be antiferromagnetic, and is strikingly different from Mn-based molecular magnets. Both of these features are explained through the inherent electronic structures of the nanoclusters. [Preview Abstract] |
|
K1.00186: The Effect of Magnetic Anisotropy on Colossal Electroresistance in Manganites Alessandra Gallastegui, Rafiya Javed, Hyoungjeen Jeen, Amlan Biswas The combined effect of long range strain interactions and disorder on a first order transition leads to micrometer scale phase separation in hole-doped manganese oxides (manganites). The coexisting phases are ferromagnetic metallic (FMM), charge ordered insulating (COI), and paramagnetic insulating (PMI) and at certain temperatures these phases behave like a fluid under the influence of magnetic and electric fields. We will present magnetotransport data on nano/micro-structures of the manganite (La$_{1-y}$Pr$_{y})_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LPCMO) which show that the FMM phase behaves like a fluid in an electric field. In fact, due to the magnetic anisotropy of our materials, the behavior of the coexisting phases is reminiscent of a ferrofluid. [Preview Abstract] |
|
K1.00187: Metal-terminated carbon based nanostructures Sahar Mirshamsi, Yan Wang, Hai-Ping Cheng Carbon based structures have attracted immense interest in many different fields and among them graphene has attracted more attention because of its unique physical properties. Hybrid metal-Carbon nanostructures are of interest because of their electronic and magnetic properties. We have studied magnetic correlations at zigzag edges of metal terminated graphene nanoribbons by calculating the transverse and longitudinal fluctuations of magnetic moments from first-principles. With inclusion of non-collinear spin-orbit coupling, we have investigated the continuous rotation of the electron spin which occurs along the ribbon edges (spin waves). Also, we report here effects of edge disorders and finite size effects. Finally, we extend our model to include multiple layers and studying the inter-layer magnetic coupling and the effect to the inter-edge magnetic coupling of the ribbon. [Preview Abstract] |
|
K1.00188: Temperature-dependent properties of the magnetic order in single-crystal BiFeO$_3$ V. Kiryukhin, M. Ramazanoglu, S-W. Cheong, W. Ratcliff, S. Lee Neutron scattering studies of the magnetic structure of multiferroic BiFeO$_3$ are presented. We report temperature dependence of the magnetic order parameter, the period of the cycloidal modulation of the antiferromagnetic order, and the populations of the equivalent magnetic domains in the monodomain ferroelectric state. No anomalies below room temperature are found, excluding the spin-reorientation transitions proposed elsewhere. [Preview Abstract] |
|
K1.00189: Polarized micro Raman spectroscopy of multiferroic BiFeO$_3$ single crystals C. Beekman, Sang-Wook Cheong, Kenneth Burch In Bismuth ferrite (BiFeO$_3$) antiferromagnetic and ferroelectric order parameters coexist at room temperature, making this material an excellent candidate for new functionalities, such as electrical control of ferromagnetism. Despite extensive reports on Raman scattering experiments on single crystals and thin films, controversy still remains in the observation and assignment of the phonon modes. However, proper Raman mode assignment to describe the phonons critical for the multiferroic behavior is necessary. We present polarized micro Raman spectroscopy of single crystals with uniform ferroelectric polarization. Careful examination of the Raman spectra upon crystal rotation enables us to unambiguously assign several (A$_1$, E$_x$ and E$_y$) modes. [Preview Abstract] |
|
K1.00190: Effect of doping and strain on N\'{e}el temperature of Cr$_{2}$O$_{3}$: An ab initio study Sai Mu, Aleksander Wysocki, Kirill Belashchenko Cr$_{2}$O$_{3}$ is a promising material for applications involving electrically switchable exchange bias [1]. For practical purposes it is desirable to enhance its N\'{e}el temperature (308K). Here we employ first principles calculations to elucidate the effect of substitutional doping and epitaxial strain on electronic structure and magnetism of Cr$_{2}$O$_{3}$. We use the supercell method and consider both transition metal (V, Ti, Mn, Fe, Co, Ni) and anion (N, B) impurities. We deduce the effect of doping on N\'{e}el temperature (T$_{N})$ by calculating the total energy change when the local moment on a transition metal impurity or on the Cr atoms near the anion impurity is flipped. We found that the transition metal impurities and N are detrimental to T$_{N}$. On the other hand, B impurities are expected to increase the Neel temperature. \\[4pt] [1] X. He. \textit{et. al. }Nature Matter. \textbf{9}, 579 (2010). [Preview Abstract] |
|
K1.00191: High-pressure synthesis and unusual metallic conductivity of the A-site-ordered perovskite CaCu$_{3}$Ir$_{4}$O$_{12}$ J.-G. Cheng, J.-S. Zhou, J.B. Goodenough Recently, much attention has been paid to the A-site-order perovskites AA'$_{3}$B$_{4}$O$_{12}$ due to the observation of a large variety of intriguing physical properties. We have prepared an A-site-ordered perovskites CaCu$_{3}$Ir$_{4}$O$_{12}$ under 9 GPa and 1250\r{ }C with a Walker-type Multianvil module. Rietveld refinements to the room-temperature x-ray diffraction pattern confirmed the cubic structure with lattice parameter a = 7.47380(6) {\AA} in the space group Im-3. Magnetic and transport properties measurements show that CaCu$_{3}$Ir$_{4}$O$_{12}$ is a paramagnetic metal with unusual temperature dependence. The inverse magnetic susceptibility $\chi ^{-1}$(T) above 80 K follows the Curie-Weiss law with $\mu _{eff}$ = 4.23 $\mu _{B}$/f.u. and $\theta _{W}$ = --233 K, while an unusual should-like feature is observed below 80 K. At the same temperature, the resistivity $\rho $(T) deviates from a T-linear behavior and exhibits a strong downward temperature dependence down to 4 K. [Preview Abstract] |
|
K1.00192: Magnetoresistance measurements in Ferro -- Antiferromagnetic bilayers based on the Ca-doped lanthanum manganite system M.E. Gomez, L. Marin, G. Ramirez, P. Prieto We studied the isothermal magnetic field dependence of the resistance behavior in ferromagnetic--antiferromagnetic interface based on the Ca-doped lanthanum manganite system at temperatures below Neel temperature of the antiferromagnetic layer. We studied the influence of the thickness of the AF-layer, $t_{AF}$, and F-layer, $t_{F}$, on the ZFC and FC magnetoresistance (MR) in La$_{2/3}$Ca$_{1/3}$MnO$_{3}(t_{F})$/ La$_{1/3}$Ca$_{2(3}$MnO$_{3}(t_{AF})$ bilayers. H$_{FC}$ was 400 Oe and the applied magnetic field, H. We systematically varied the $t_{F}$ and $t_{AF}$ thickness, maintaining constant the total bilayer thickness ($d =$ $t_{F} + t_{AF})$. We found that MR has hysteretic behavior as observed in [La$_{2/3}$Ca$_{1/3}$MnO$_{3}(t_{F})$/La$_{1/3}$Ca$_{2(3}$MnO$_{3}(t_{AF})$]$_{N}$ superlattices, but; MR increases with the increasing field from H=0 to a maximum and then decreases continuously. This behavior also appears for negative fields in both ZFC and FC loops. The position and magnitude of the maximum is not symmetric with respect to the axis H=0. [Preview Abstract] |
|
K1.00193: Characterization of EuO$_{1-x}$ thin films grown by oxidation of metallic Eu B. Colwell, A. Kinsey, S. Schlotter, M. Eblen-Zayas EuO$_{1-x}$ is of interest due to the similarities between its magnetic and transport properties and those of the manganites, and it also holds potential for spintronics applications. We have grown polycrystalline EuO$_{1-x}$ films by oxidizing metallic Eu films. The films are characterized by x-ray diffraction, as well as measuring the resistivity and magnetization responses as a function of temperature. We will report on the relationship between the growth conditions and the properties of these samples, including a description of how annealing impacts the film properties. [Preview Abstract] |
|
K1.00194: Composition Dependence of the Anomalous Hall Effect in L10 FePt Thin Films M. Allison, T. George, P. Kharel, D. Sellmyer, Y. Huh FePt multi-layered thin film systems were investigated as to its composition effect on the anomalous hall effect. Thin bilayers of FePt were sputter-deposited in series of variable thicknesses on to a thermally oxidized substrate of SiO2. The total thickness of samples was controlled to be 12 nm. XRD and SEM were used to confirm structure and composition of thin films for systematic characterization. Resistivity and Magnetization measurements were studied at room temperature and low temperature using SQUID magnetometer. The minimal resistivity exists near 54{\%} of Fe concentration. The anomalous hall effect dominates as Fe concentration increases. Hall angles drop rapidly at the both high and low Fe concentration while it exhibits a plateau-like dip near 54{\%} of Fe concentration. [Preview Abstract] |
|
K1.00195: Imaging and Electric Control of Boundary Magnetization and Exchange Bias in Chromia and Chromia/CoPd Xi He, Ning Wu, Yi Wang, Alekasander Wysocki, Takashi Komesu, Kirill Belashchenko, Peter Dowben, Christian Binek, Uday Lanke, Anthony Caruso, Elio Vescovo Promising spintronic concepts utilize electric control of boundary magnetization. Symmetry arguments predict that the magnetoelectric antiferromagnet (AF) Cr$_{2}$O$_{3}$, has a roughness insensitive surface magnetization which is coupled to the bulk AF order parameter. We provide macroscopic and microscopic evidence for this surface magnetization and its electric control. The latter is exploited in perpendicular exchange bias heterostructures where a ferromagnetic Pd/Co multilayer is deposited on the (0001) surface of a Cr$_{2}$O$_{3}$ single crystal. These heterostructures show reversible, room-temperature voltage-controlled switching of the exchange-bias field between positive and negative values.\footnote{Xi He, et al. Nature Materials \textbf{9}, 579 (2010)} This work is supported by NSF Career, NSF MRSEC, NRI, and Research Corporation. [Preview Abstract] |
|
K1.00196: Effect of carbon doping on optical constants of half-metallic ferromagnet Mn$_{5}$Ge$_{3}$ N. Stojilovic, Rongwei Hu, C. Petrovic, S.V. Dordevic Mn$_{5}$Ge$_{3}$ is an intermetallic ferromagnetic compound with the high Curie temperature ($T_{C}$ = 296 K), a high spin polarization ($P$ = 42{\%}), and a good lattice match to germanium. Doping of Mn$_{5}$Ge$_{3}$ with carbon increases $T_{C}$ above room temperature and makes these compounds promising candidates for spin injectors for potential spintronics applications. In this study we employ optical spectroscopy to measure near-normal reflectance in the frequency range from far-infrared to ultraviolet (70 -- 50000 cm$^{-1})$ at temperatures between 10 and 300 K. In particular, we study the effect of carbon doping on the optical constants to gain a better insight into how it affects the electronic properties of the parent compound. [Preview Abstract] |
|
K1.00197: Spin polarization measurements in Fe$_{4}$N/MgO/NbN tunnel junctions using quasiparticle tunneling spectroscopy Takayuki Hohjo, Keita Sakuma, Tetsuya Miyawaki, Kenji Ueda, Hidefumi Asano, Yosuke Komasaki, Masakiyo Tsunoda In spintronic applications, it is thought that Fe$_{4}$N is useful because it has been theoretically expected to have high spin polarization. Fe$_{4}$N/MgO/CoFeB magnetic tunnel junctions (MTJs) were fabricated, and an inverse tunnel magnetoresistance (TMR) effect was reported by our groups. However, spin polarization of Fe$_{4}$N is yet incompletely understood. We investigated spin polarization of Fe$_{4}$N, using quasiparticle tunneling spectroscopy (QTS), and the measured spin polarization of Fe$_{4}$N was compared with that in Fe$_{4}$N/MgO/CoFeB MTJs. Spin polarization of ferromagnetic materials can be directly measured by QTS. By using NbN and MgO as superconducting electrode and barrier layers, respectively, Fe$_{4}$N/MgO/NbN tunnel junctions were fabricated by magnetron sputtering. The thickness of MgO barrier layer was varied from 1.0 to 1.5 nm. The areal resistances of the Fe$_{4}$N/MgO/NbN tunnel junctions were close to those of Fe$_{4}$N/MgO/CoFeB MTJs, which had the same thickness of MgO barrier layer as those Fe$_{4}$N/MgO/NbN tunnel junctions. In QTS, spin polarization of Fe$_{4}$N was estimated to be $\sim -$0.68. This value is larger than spin polarization in MTJs. [Preview Abstract] |
|
K1.00198: Temperature and temporal evolution of nonlocal spin signals Yi Ji, Han Zou An unusual temperature evolution of spin signals has been previously reported by others for metallic nonlocal spin valves (NLSV): The spin signal increases as the temperature decreases from room temperature, reaches a maximum value around 50 K, and then decreases as the temperature approaches 4 K. This has been interpreted as due to a high surface spin-flip rate, but the origins of which are yet to be understood. In this work, we show that for an as fabricated Py-Cu NLSV device this temperature dependence is clearly observed. The device was then stored in the ambient environment for a period of 5 months. Afterwards, we found an increase of the spin signals, and more interestingly the spin signal levels off at 27 miliohms, instead of decreasing, below 50 K. Based on this and our other experiments, we conclude that the surface spin-flip scattering originates from the magnetic impurities embedded in the Cu channel near the side surfaces. Upon oxidizing the Cu, the surface impurities are buried in the copper oxide and become less accessible to the conduction electrons. Therefore the surface spin-flip rate is reduced over time. [Preview Abstract] |
|
K1.00199: Spin-transfer induced vortex dynamics with non-standard angular dependence torque Paolo Bortolotti, Nicolas Locatelli, Vincent Cros, Julie Grollier, Rita Machedo, Ricardo Ferreira, Susana Cardoso, Albert Fert Microwave emissions driven by spin-transfer were firstly observed on FeNi/Cu/FeNi pillars (standard samples) characterized by uniform magnetization. Interestingly, by tuning the spin accumulation profile, i.e., choosing Co/Cu/FeNi pillars with opportune ratio of thickness/spin diffusion length (non-standard samples), it is possible to obtain strong modification of the torque angular dependence and, more generally, of the magnetization dynamics itself. Eventually, oscillations at zero applied field were observed for these non-standard pillars, again for uniform magnetization. However, when a large current density is applied, the uniform hypothesis is broken and vortex states are favoured. In this work we want to stress that non standard-angular dependence, obtained for such Co/Cu/FeNi samples, plays an important role also for vortex dynamics. By the combined study of static and dynamic response, we can discriminate among all possible combinations of vortex chiralities and polarities. The evolution with field and current of such configurations clearly differs from samples with standard spin-torque angular dependence, resulting in a different dynamics for such non-standard samples. [Preview Abstract] |
|
K1.00200: Size effect on GdMn$_{2}$O$_{5}$ nanoparticles Cheng-Yu Weng, Chun Chuen Yang, Wei-Luen Huang, Zhe-An Jian, Yang Yuan Chen We fabricated six difference sizes of GdMn$_{2}$O$_{5}$ nanoparticles/nanobrick by hydrothermal method. Purity and particle size were determinate by x-ray diffraction and TEM/SEM images. Two Mn antiferromagnetic ordering peaks at around 38 and 40 K were observed in ac magnetic susceptibility experiments, where as particle size is larger than 60 nm. Curie-Weiss fitting revealed that the N\'eel temperatures are increased with increasing size. Similar phenomena were also found in the saturate magnetic moments obtaind from M-H experiments at 5 K. No hysteresis loops were found in any particle size. We believe these magnetic behaviors are correlated with size confinement effects. The estimated magnetic correlation length of Mn is in between 60 and 84 nm. [Preview Abstract] |
|
K1.00201: Anisotropic paramagnetism in monoclinic Nd$_{2}$Ti$_{2}$O$_{7}$ single crystals Hui Xing, Gen Long, Hanjie Guo, Youming Zou, Chunmu Feng, Guanghan Cao, Hao Zeng, Zhuan Xu The anisotropic paramagnetism and specific heat in Nd2Ti2O7 single crystals are investigated. Angular dependence of the magnetization and Weiss temperatures show the dominant role of the crystal field effect in the magnetization. By incorporating the results from the diluted samples, contributions to Weiss temperature from exchange interactions and crystal field interactions are isolated. The exchange interactions are found to be ferromagnetic, while the crystal field contributes a large negative part to the Weiss temperature, along all three crystallographic directions. The magnetic specific heat reveals a two-level Schottky ground state scheme, due to the Zeeman splitting of the ground state doublet, and the g-factors are thus determined. These observations provide solid foundations for further investigations of Nd2Ti2O7. [Preview Abstract] |
|
K1.00202: Magnetic Order and Spin Dynamics in a Hexagonal Rare Earth Manganite J.S. Helton, D.K. Singh, S. Elizabeth, S. Harikrishnan, J.W. Lynn Hexagonal rare earth manganites, \emph{R}MnO$_{3}$ (\emph{R} = Dy, Ho, Er, Tm, Yb, Lu, Y, or Sc), have attracted a great deal of recent attention as magnetoelectric multiferroics as most of these systems are ferroelectric at room temperature and display magnetic order below $T_{N} \approx$ 100 K. This magnetic order can be quite complex, as both the \emph{R} and Mn ions lie on geometrically frustrated triangular lattices. DyMnO$_{3}$ is typically orthorhombic, but can also be grown in the hexagonal phase; Dy$_{0.5}$Y$_{0.5}$MnO$_{3}$ displays the hexagonal phase and is magnetically diluted at the rare earth site. We have used neutron scattering experiments to explore the magnetic structure and spin dynamics of Dy$_{0.5}$Y$_{0.5}$MnO$_{3}$. [Preview Abstract] |
|
K1.00203: Z$_2$ topological classification of the $S=1/2$ Heisenberg model on the two dimensional pylochlore lattice Sho Tanaya, Mitsuhiro Arikawa, Isao Maruyama, Yasuhiro Hatsugai We have investigated the $S=1/2$ Heisenberg model on the two dimensional pyrochlore lattice [1] by using the Z$_2$ Berry phase [2] which is quantized due to the time reversal invariance. Since these Z$_2$ Berry phases are adiabatic invariants against change of the physical parameters, one can distinguish ground states when the quantized values are different. By suitably choosing ways of local $U(1)$ twists to define the Berry phases, one can show that the ground state in this system is adiabatically connected to a direct product state of local singlets or plaquette singlets. We have described the basic formulation and demonstrate the validity for finite systems using a Lanczos diagonalization. \\[4pt] [1] J.-B. Fouet, M. Mambrini, P. Sindzingre, and C.Lhuillier, Phys. Rev. B 67 (2003) 054411.\\[0pt] [2] Y. Hatsugai, J.Phys Soc. Jpn. 73 (2004) 2604. [Preview Abstract] |
|
K1.00204: Chirality waves in two-dimensional magnets Dmitry Solenov, Dmitry Mozyrsky, Ivar Martin Electron, as a particle with spin 1/2, moving though a magnetic material with non-coplanar magnetization pattern accumulates quantum mechanical (Berry) phase, characterized by the degree of non-coplanarity of the magnetic texture, or chirality. Until now metallic chiral magnets were thought to be quite rare and require either a fine tuning of the electron spectrum (nesting) or spin-orbit interactions. We show that two-dimensional magnets within a simple model of magnetism -- a Kondo lattice model -- favor a non-coplanar order (a distorted skyrmionic lattice) with unidirectional modulated chirality. Unlike recently observed chiral triangular skyrmion lattices supported by spin-orbit interaction and finite magnetic field (e.g. in MnSi), the chirality-wave order emerge at small-to-intermediate Kondo coupling strength in the absence of magnetic field or spin-orbit coupling [Preview Abstract] |
|
K1.00205: Non-polar electromagnon in hexa-YMnO$_{3}$ J.R. Simpson, A.B. Sushkov, H.D. Drew, M. Mostovoy, A. Gozar, G. Blumberg, N. Lee, S.-W. Cheong Coupled magnon-phonon excitations in magnetic materials have been observed in multiferroic materials and involve the polar optical phonons. Such excitations may be more general, occurring in non-ferroelectric magnets and involving non-polar (Raman or silent) phonons. Temperature-dependent Raman spectra of low-frequency excitations in single-crystal h-YMnO$_{3}$ are measured using a triple-grating spectrometer. We compare the spectral intensity of magnons to changes in the Raman-active phonons above and below the Neel temperature. Raman and infrared experimental results on h-YMnO3 demonstrate that the 5 meV hybrid mode observed in neutron scattering is an example of a Raman electromagnon. [Preview Abstract] |
|
K1.00206: T1-limited Nitrogen-Vacancy magnetometry of fluctuating AC magnetic fields Carlos Meriles, Abdelghani Laraoui, Jonathan Hodges Nitrogen-Vacancy (NV) centers in diamond are being actively investigated as a platform for nanoscale magnetic field sensing. In many of the envisioned applications the target AC magnetic field fluctuates over time and cannot be triggered in synchrony with the pulse protocol controlling NV evolution. Here we introduce a scheme to characterize the time correlation of the unknown field over a time interval limited by the NV spin-lattice relaxation time. Our approach uses two consecutive Hahn-echo sequences separated by a time interval of variable duration. We present an initial experimental demonstration of the technique using an engineered AC field and discuss possible extensions to the monitoring of slowly fluctuating spin ensembles. [Preview Abstract] |
|
K1.00207: SUPERCONDUCTIVITY |
|
K1.00208: $^{13}$C NMR Study of Graphite Intercalated Superconductor CaC$_6$ Crystals in the Normal State Moohee Lee, Sung Hoon Kim, Ki Hyeok Kang, B. J. Mean, B. Ndiaye, Jun Sung Kim $^{13}$C NMR(Nuclear Magnetic Resonance) measurements have been performed to investigate the local electronic structure of a superconducting graphite intercalation compound CaC$_6$ ($T_c$ = 11.4 K). A large number of single crystals were packed and sealed in a quartz tube for naturally abundant $^{13}$C NMR. Spectrum, Knight shift, linewidth, spin-lattice relaxation time $T_1$, and the spin-spin relaxation time $T_2$ were measured in the normal state as function of temperature down to 70 K at 4.8 T and 8.0 T. $^{13}$C NMR spectrum shows a narrow peak with a very small Knight shift. Knight shift and linewidth of the $^ {13}$C NMR are almost temperature-independent around, respectively, 0.012\% and 1.2 kHz. The spin-lattice relaxation rate $1/T_1$ is proportional to temperature confirming a Korringa behavior as for nonmagnetic metals. The Korringa product is measured to be $T_1T$= 210 s.K. From this value, the Korringa ratio is deduced to be $\xi$ = 0.73, close to unity, which suggests that the independent-electron description works well for CaC$_6$, without complexity arising from correlation and many-body effects. [Preview Abstract] |
|
K1.00209: Oxygen staging in phase separated La$_{2-x}$Sr$_{x}$CuO$_{4+y}$ Hashini Mohottala, Linda Udby, S. Emery, B.O. Wells, J.I. Budnick, Christof Nidermayer, Kim Lefmann, N.H. Anderson, F.C. Chou We studied oxygen staging in a series of La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO) samples using neutron scattering. The samples were oxidized using electrochemistry. Electronic phase separation was previously reported in the oxygen rich LSCO system with two stable phases identified as optimally doped superconducting phase and a magnetic phase (1/8th like) with the same ordering temperatures at 40 K . Our present studies show staging in this system. Although staging was observed and extensively studied in the samples with no Sr, it has not been reported or systematically studied in the systems with both Sr and oxygen. We do find staging in the oxygenated LSCO system, but the staging peaks evolve as Sr concentration increases and excess oxygen concentration decreases. [Preview Abstract] |
|
K1.00210: Muon probing in optimal and under- doped GdBCO C. Boekema, H. Sio, M.C. Browne By means of MaxEnt-Burg, transverse-field (TF) $\mu $SR data of underdoped ($\delta $1; T$_{c }$= 81 K) and optimal doped ($\delta $0; T$_{c }$= 93 K) GdBa$_{2}$Cu$_{3}$O$_{7-\delta }$ (GdBCO) are analyzed. Site search studies for RBCO generated plausible candidates for muon sites [1] called the Balmer and Lin sites. We wish to confirm the muon-probe sites in GdBCO.~One of the two Balmer sites and the Lin site are located near O vacancies. These two sites become unstable in underdoped GdBCO($\delta $1). Positive muons are repelled by the positive O vacancies. This repulsion effects would be more pronounced as temperature increases.~ At 120 K, three signals are present in GdBCO($\delta $1), while at roomtemperature (RT), only one dominant signal remains. In contrast, three signals occur at 120 K and RT for GdBCO($\delta $0), which has much less O vacancies.~ These results support earlier studies [1] of muon-O sites.~Thus, the muons probe away from the CuO$_{2}$ plane, allowing $\mu $SR to detect magnetic fields originating from potential loop currents in these planes. [2] By ME-$\mu $SR analysis, the Balmer {\&} Lin sites in GdBCO are confirmed. Research supported by NSF-REU. \\[0pt] [1] WK Dawson et al, J Appl Phys 64 (1988) 5809 {\&} Hpf Int 63 (1990) 219.\\[0pt] [2] CM Varma, PRL 83 (1999) 3538; T Songatikamas et al, J Superconductivity and Novel Magn 23 (2010) 793. [Preview Abstract] |
|
K1.00211: Strongly anisotropic flux pinning in superconducting PbBi thin films covered by periodic ferromagnet stripes Donald Naugle, Zyxin Ye, Wenhao Wu, Igor Lyuksyutov We have studied the vortex pinning via their magnetic interaction with a periodic structure of parallel magnetic stripes. Superconducting lead-bismuth (82{\%} Pb and 18{\%} Bi) alloy films were covered by an insulating Ge layer and periodic a Ni array of magnetic stripes fabricated on the top of the Ge layer by electron-beam lithography and thermal evaporation. The critical current density was significantly stronger when the current was applied parallel to the stripes than when the current was perpendicular to the stripes. This is attributed to the barrier to the vortex motion provided by the magnetic interaction with magnetic stripes. The enhancement in critical current was most significant at temperatures close to the superconducting transition temperature. [Preview Abstract] |
|
K1.00212: Effect of current on the dc I-V characteristic of polycrystalline YBa$_{2}$Cu$_{3}$O$_{7-X}$ near Tc Snehadri Ota The dc I-V characteristic of polycrystalline YBa$_{2}$Cu$_{3}$O$_{7-X}$ high temperature superconductors (HTSC) is measured near the transition temperature (T$_{c})$. The T$_{c}$ was found to be 90 K with a width of 2 K. The voltage was measured at various current values and with reversing the current. A difference in voltage was found, for forward and reverse current direction near T$_{c}$. This can be understood qualitatively as due to the d-wave superconductivity as predicted by the RVB theory. This can also be understood qualitatively as due to the presence of proximity junctions, which is generally indicated by finite transition width in HTSC or A15 superconductors. The observed directionality of the I-V characteristic can be understood in terms of trapped flux by the self-field of the current and the proximity junctions in these materials. [Preview Abstract] |
|
K1.00213: Superconducting and transport properties of Y$_{3}$Ba$_{5}$Cu$_{8}$O$_{X}$ and Y$_{3}$Ca$_{2}$Ba$_{5}$Cu$_{8}$O$_{x}$ prepared by sol-gel method Ali Er, Yuksel Ufuktepe, Ahmet Ekicibil, Ali Osman Ayas, Selda Kilic Cetin, Kerim Kiymac The influence of substitution of Ca has been studied using electrical resistivity ($\rho )$, X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive analysis (EDX), differential thermal analysis (DTA), thermogravimetric analysis (TGA), Hall coefficient (R$_{ H})$, Hall mobility ($\mu _{H})$ and magnetoresistance measurements. The XRD spectra showed that they almost have the same crystal structure of Y$_{3}$Ca$_{2}$Ba$_{5}$Cu$_{8}$O$_{x}$ as Y$_{3}$Ba$_{5}$Cu$_{8}$O$_{x }$with some impurities peaks. The resistivity measurements were made by the four-probe method. The Y$_{3}$Ba$_{5}$Cu$_{8}$O$_{x }$ and Y$_{ 3}$Ca$_{2}$Ba$_{5}$Cu$_{8}$O$_{x}$ have the highest T$_{c}$-onset at about 92.7 and 86.6 K, respectively. The Hall coefficient R$_{H}$ and Hall mobility $\mu _{H}$ are measurement between 10-300 K temperatures at magnetic field of 0.55 T. The sign of R$_{H}$ and $\mu _{H}$ are positive for two samples which indicate that the conduction is $p$-type for the samples. A small change of normal state resistivity and superconducting transition are observed in the resistivity curve with the magnetic field. [Preview Abstract] |
|
K1.00214: Dynamical conductivity at the dirty superconductor-metal quantum phase transition J.A. Hoyos, Adrian Del Maestro, Bernd Rosenow, Thomas Vojta We study the transport properties of ultrathin disordered nanowires in the neighborhood of the superconductor-metal quantum phase transition. To this end we combine numerical calculations with analytical strong-disorder renormalization group results. The quantum critical conductivity at zero temperature diverges logarithmically as a function of frequency. In the metallic phase, it obeys activated scaling associated with an infinite-randomness quantum critical point. We extend the scaling theory to higher dimensions and discuss implications for experiments. [Preview Abstract] |
|
K1.00215: Spatially resolved NMR spectra for the Swiss cheese model in heavy fermion PuCoGa$_5$ superconductor Tanmoy Das, Jian-Xin Zhu, A.V. Balatsky, M.J. Graf Spatially resolved NMR experiments, which probe the local electronic excitations, play a vital role for studying the pairing symmetry of unconventional superconductors. Here we calculate the spatial modulation of the NMR spin-lattice relaxation rate (1/T1) for the Swiss cheese model as a function of impurity concentration in PuCoGa5 superconductor. The local suppression of the superconducting order parameter due to impurities is related to the number of holes in the Swiss cheese model. Our results indicate that Friedel-like oscillations,as seen in the local-density of states near an impurity, are also present in the behavior of 1/T1 as one moves away from the impurity site. We demonstrate that the gap nodes, which are filled by disorder, can be probed by NMR through the local information encoded in the spectra. The advantage of spatially resolved NMR compared to STM measurements is that the former probe is not sensitive to surface states. Work is supported by US DOE. [Preview Abstract] |
|
K1.00216: Sun Oven Grown Cuprates Superconductivity and Periodic Lattice Distortions PLD Juana V. Acrivos, J.G. Chidvinadze, D.D. Gulanova, D. Loy Bi$_{1.7}$Pb$_{0.3}$Sr$_{2}$Ca$_{n-1}$Cu$_{n}$O$_{4+2n+\delta }$ identified by the layer heavy element composition with substitution, s (2$_{s}$:2:n-1:n\underline {$>$}2) cuprates grown by green chemistry, transition temperatures to superconductivity T$_{c}$=87 to 150K are related to their structure. Enhanced XRD at energies near but below the Cu K, and Pb and Bi L3-edges for pure n=2, 3 phases show Darwin shaped preferred [HKL] reflections that identify the magnitude of the allowed transition moment from the core state to extended unoccupied states determined by the electron density symmetry in that plane, confirmed by XAS of 3$\mu $m thick films. Weak PLD are still detected, but the stability gained by substitution of Bi by Pb is the formation of nearly symmetric Pb$_{8}$ cubes in (2$_{s}$:2:1:2)$_{13 }$and (2$_{s}$:2:2:3)$_{17}$ super-lattices. The preferred 2D [HKL] reflection planes play the same role in the chemical activity of 3D solids as the linear bonds do in molecular reactions, governed by scattering dependent on the electron density symmetry in their highest and lowest unoccupied states. [Preview Abstract] |
|
K1.00217: Distribution of Co-dopants in LaFe1-xCoxAsO single crystals Jiaqiang Yan, R.W. McCallum, T.A. Lograsso LaFe1-xCoxAsO single crystals have been grown in NaAs flux under ambient pressure. The content and distribution of Co-dopants were studied with wavelength dispersive x-ray spectroscopy. The plate-like single crystals consisit of multilayers with the thickness about 2 $\mu$m. No variation of Co content was observed in one single layer. However, Co content was observed to change gradually along the thickness (or z-) direction, which suggests layer-by-layer growth mechanism. The relation between the Co-content in crystals and starting materials was developed and the distribution coefficient of Co-dopants was estimated to be around 0.60. [Preview Abstract] |
|
K1.00218: Epitaxial growth of the electron-doped Sr$_{1-x}$La$_{x}$CuO$_{2}$ by magnetron spattering Keita Sakuma, Hiroyuki Akatsuka, Tetsuya Miyawaki, Kenji Ueda, Hidefumi Asano The electron-doped Sr$_{1-x}$La$_{x}$CuO$_{2}$ (SLCO) has the simplest structure among high temperature superconductors (HTS). In addition, transition temperature of SLCO is the highest among electron-doped HTS. Therefore, SLCO is suitable for fundamental researches and electronic applications. Several groups reported growth of $c$-axis oriented SLCO thin films on various substrates, however $a$-axis oriented SLCO thin films, which are useful for superconductor junctions, have not been obtained. In this study, we deposited SLCO thin films on various substrates [(001) KTaO$_{3}$(KTO), SrTiO$_{3}$(STO), MgO and LaAlO$_{3}$(LAO)] by magnetron sputtering. KTO and STO have better lattice matching to SLCO[100] compared with MgO and LAO. SLCO thin films on KTO and STO were $c$-axis obtained. On the other hand, SLCO thin films on MgO and LAO were (101) and$ a$-axis oriented, respectively. We considered that the differences of crystal orientations in these films were caused by lattice matching to the substrates. These results indicated that we can control crystal orientation of SLCO thin films using substrates with various lattice constants. [Preview Abstract] |
|
K1.00219: Superconductivity in Zr$_{2}$(Co$_{1-x}$M$_{x})$ (M = Cu, Ga) K.J. Syu, C.H. Wu, H.H. Wu, S.C. Chen, H.H. Sung, W.H. Lee As revealed in the powder x-ray diffraction and crystallographic data, the body-centered tetragonal structure of the parent compound Zr$_{2}$Co is retained in both Zr$_{2}$(Co$_{1-x}$Cu$_{x})$ and Zr$_{2}$(Co$_{1-x}$Ga$_{x})$ systems with the solubility limit near $x$ = 0.3. The refined lattice parameters indicate that there is a movement for $c$ to decrease and $a$ to increase, due to the doping with Cu or Ga in the compound. Since the percentage change in lattice parameters $c$ and $a$ is comparable, a prominent peak in the unit cell volume $v$ versus $x$ curve therefore appears around$ x$ = 0.15 and $x$ = 0.2 for Zr$_{2}$(Co$_{1-x}$Cu$_{x})$ and Zr$_{2}$(Co$_{1-x}$Ga$_{x})$ systems, respectively. Magnetic and electrical measurements show that there is an explicit maximum T$_{c}$ close to $x$ = 0.05 for both systems. As compared with the Zr$_{2}$(Co$_{1-x}$Ni$_{x})$ system$^{1}$, it may imply that the superconducting transition temperature in Zr$_{2}$(Co$_{1-x}$Cu$_{x})$ and Zr$_{2}$(Co$_{1-x}$Ga$_{x})$ relate more to the spin density fluctuations than to the density of states at the Fermi level. $^{1}$M. Takekuni, H.Sugita and S. Wada, Phys. Rev. B \textbf{58}, 11698 (1998). [Preview Abstract] |
|
K1.00220: Plausible loop currents in the GdBCO pseudogap phase C. Boekema, T. Songatikamas, M.C. Browne For the cuprate pseudogap phase, Varma [1] predicts loop currents above T$_{c}$. We search for fields near 100 Oe, created by such currents in GdBa$_{2}$Cu$_{3}$O$_{7-\delta }$ (GdBCO). Using MaxEnt-Burg (ME) we analyze zero-field (ZF) muon-spin-rotation ($\mu $SR) data of underdoped ($\delta $1; T$_{c }$= 81 K) and optimal doped ($\delta $0; T$_{c }$= 93 K) GdBCO. [2] ME-$\mu $SR applied to ZF-GdBCO data yields T-dependent signals at 0-MHz (f0) and 0.3-MHz (f1) and hints of 1.4-MHz signals. To cancel any systematic (f1) effect, we analyze DS(t,T) = S(t,T$>$T$_{c})$ - S(t,T'$<<$T$_{c})$. This ME-Burg analysis of GdBCO($\delta $0 {\&} $\delta $1) indicates weak signals near 1.4 MHz above T$_{c}$ (and f1 disappears). These ME-peaks occur at $\sim $1.3 MHz (95 Oe) for GdBCO($\delta $1) and $\sim $1.5 MHz (110 Oe) for GdBCO($\delta $0). These $\mu $SR signals, plausibly due to fields created by loop currents, appear only above T$_{c}$. Below T$_{c}$, only ME background noise exist in DS(t,T) transforms.~The $\sim $1.4-MHz peak intensity to background ratio at its maximum is $\sim $5 for GdBCO($\delta $1) and $\sim $4 for GdBCO($\delta $0) at $\sim $10 degrees above T$_{c}$. Validating predicted loop currents is essential for understanding the pseudogap phase. Research supported by REU NSF {\&} DOE LANL. [1] CM Varma, Phys Rev Lett 83 (1999) 3538; [2] T Songatikamas et al, J Supercond {\&} Novel Magn 23 (2010) 793. [Preview Abstract] |
|
K1.00221: Modeling Superconducting properties of an inhomogeneous mixture of doped metallic and semiconductor carbon nanotubes Ilya Grigorenko, Anvar Zakhidov We considered theoretically the superconducting properties of a bundle of boron-doped carbon nanotubes, which consists of two types of nanotubes: semiconducting and metallic. The tubes are assumed to be close-packed, making a hexagonal lattice in the transverse section of the bundle. The properly doped semiconducting nanotubes are assumed to have a higher transition temperature than metallic because of the lower lying Van Hove singularities in the DOS (proven in experimentally found Kataura plot). We used an inhomogeneous microscopic model to describe the proximity effects between the two different types of tubes, and calculated the averaged superconducting critical temperature for the bundle given a ratio between the metallic and semiconductor nanotubes. We found that the critical temperature scales approximately quadratically as a function of the ratio. We also discuss briefly the possible effect of metallic nanotubes on the suppression of the phase fluctuations in 1-D superconducting pairing in properly doped semiconducting nanotubes. [Preview Abstract] |
|
K1.00222: Study of Mini-Gap Regime in Au Nanowires Brian Cooper, Jian Wang, Moses Chan, Meenakshi Singh, Mingliang Tian, Jainendra Jain The inducement of superconductivity in 70nm single crystal Au nanowires (AuNWs) via the Proximity Effect was reported in 2009 [Wang, J. et al. \textit{Phys. Rev. Lett.} \textbf{2009}, 102, 247003]. This study, carried out on 3 AuNWs of different lengths (1.0, 1.2 and 1.9 $\mu $m), showed a precipitous drop in the resistance to a fully superconducting state of the 1.0um wire; while the 1.2$\mu $m wire made the transition in 2 steps, and the 1.9$\mu $m wire never fully transitioned to a zero resistance state. This behaviour lead to the coinage of the so-called ``mini-gap'' phase in proximity induced superconducting nanowires. We are currently investigating the robustness of this ``mini-gap'' regime by parametric variations to the gold nanowire system. Looking at features such as crystallinity, AuNW diameter, electrode material, and directional magnetic field dependence, we are attempting to further illuminate the nature of this new ``mini-gap'' state. [Preview Abstract] |
|
K1.00223: Coherent pairing and phase separation in small negative U Hubbard nanoclusters away from half filling Kalum Palandage, Gayanath Fernando, Armen Kocharian The similarities and differences in the mechanism of electron pairing instabilities, driven by attractive and repulsive electron interaction, are studied in the ensemble of small clusters for one hole off half filling under variation of interaction strength and temperature. These exact calculations of charge and spin collective excitations, and corresponding critical transition temperatures yield intriguing insights into the level crossing degeneracies, phase separation transitions, condensation and formation of spatial inhomogeneities in various cluster geometries [Ultramicroscopy 109, 1066 (2009)]. Separate condensation of electron charge and spin degrees in negative U model away of half filling offers a new route for the mechanism of superconductivity in inhomogeneous systems, different from the quasi-particle BCS scenario for electron condensation. Phase diagrams resemble a number of inhomogeneous, coherent and incoherent nanoscale phases seen in various positive Hubbard cluster geometries in high Tc cuprates, iron pnictides, and other transition metal oxides. [Preview Abstract] |
|
K1.00224: Dynamics of an RF-driven Josephson junction near the bifurcation point Amrit Poudel, Maxim Vavilov We investigate the dynamics of an RF driven Josephson junction coupled to thermal heath bath. We present a stochastic semiclassical equation of motion for the junction, obtained from a microscopic Hamiltonian of the system. We discuss conditions when the Langevin forces in this equation can be approximated by Markovian white noise. For this case, we obtain the Fokker-Planck equation, which we numerically solve to describe the switching process between two stable states near the bifurcation point. [Preview Abstract] |
|
K1.00225: Effects of 3d magnetic metal substitutions (Fe, Co, Ni) for V on superconducting T$_{c}$ of the ZrV$_{2}$ system Wun-Hsin Lee, D.H. Chen, K.J. Syu, S.C. Chen, H.H. Sung The effects of Fe, Co and Ni substitution on the crystallographic data and superconducting transition temperature (T$_{c})$ of ZrV$_{2}$ have been investigated through powder x-ray diffraction, static magnetization and electrical-resistivity measurements. Variation of the room temperature refined lattice parameters indicate that there is a movement for $a$ and unit cell volume $v$ to decrease, linearly with increasing $x$ up to 0.4, for the Zr(V$_{2-x}$T$_{x})$ (T = Fe, Co and Ni) alloys. Magnetic and electrical measurements show that the superconducting transition temperature (T$_{c})$ of ZrV$_{2}$ is reduced by the doping of Fe, Co and Ni with depression rate dT$_{c}$/dx $\sim $ -14, -17.5, and -15 K/atom {\%}, respectively. The doping of Co has a larger effect than Fe and Ni on the decrease of T$_{c}$. [Preview Abstract] |
|
K1.00226: Superconducting Properties of Lead-Bismuth Films Controlled by Ferromagnetic Nanowire Arrays Zuxin Ye, Igor F. Lyuksyutov, Wenhao Wu, Donald G. Naugle Superconducting properties of lead-bismuth (82{\%} Pb and 18{\%} Bi) alloy films deposited on ferromagnetic nanowire arrays have been investigated. Ferromagnetic Co or Ni nanowires are first electroplated into the columnar pores of anodic aluminum oxide (AAO) membranes. Superconducting Pb$_{82}$Bi$_{18}$ films are then quench-condensed onto the polished surface of the AAO membranes filled with magnetic nanowires. A strong dependence of the Pb$_{82}$Bi$_{18 }$superconducting properties on the ratio of the superconducting film thickness to the magnetic nanowire diameter and the material variety was observed. [Preview Abstract] |
|
K1.00227: Magnetic nanorod - superconductor hybrid near the superconducting transition temperature K. Kim, I. Lyuksyutov, D.G. Naugle We report measurements of the magnetoresistance and phase diagram of a lead-bismuth (82{\%} Pb and 18{\%} Bi) superconducting film with an embedded square array of Ni nanorods near the superconducting transition temperature. Magnetoresistance above Tc demonstrates oscillations compatible with flux quantization through the unit cell of the magnetic nanorod array. Strong hysteresis of the superconducting properties and an apparent increase of the second critical field is found. [Preview Abstract] |
|
K1.00228: Description of a primitive valley scattering unit cell to understand anisotropic inter-valley scattering in AlAs quantum wells S. Prabhu-Gaunkar, M. Grayson Valley degenerate systems have an extra scattering channel not present in single valley systems, namely inter-valley scattering. To help classify anisotropic inter-valley scattering in degenerate multi-valley systems, such as AlAs quantum wells (QWs), we define a valley scattering primitive unit cell in momentum space which allows one to distinguish purely in-plane momentum scattering from scattering requiring an out-of-plane momentum component. The standard depiction of a 2D Brillouin zone of a quantum confined valley-degenerate system projects all valleys to a single plane and this depiction loses information about the momentum scattering component that was projected out. Because QW confinement potentials are inherently anisotropic, the disorder potential characteristic of quantum confinement can create anisotropic short-wavelength inter- valley scattering potentials favoring in-plane momentum scattering. We demonstrate that the valley scattering cell for AlAs QWs grown along various orientations is particularly useful in identifying relevant scattering vectors. Initial estimates will be shown of the role of strong electron-electron interactions in AlAs QWs on inter-valley scattering parameters such as inter-valley scattering time, probabilities and rates. [Preview Abstract] |
|
K1.00229: Analytical approach to neutron scattering on solitons in low dimensional systems Irina Bariakhtar, Yaroslav Nazarenko It is well known that neutron scattering, along with x-ray scattering, allows for the study of condensed matter system structures. Recently, it was revealed that in magnetic materials some nonlinear formations such as solitons of the topological type of excitation - kinks, solitons with zero topological charge - breathers, and solitons with linear excitation, analogous to spin waves, may arise. In this paper, we present the polarized neutron scattering approach for the study of such formations in magnetic materials. The formulas for the cross sections of scattering in the low-dimensional systems with solitons were obtained. We have presented the calculations for kink type solitons. Similar calculations can also be presented for breather-type solitons. We have shown that the study of neutron polarization after scattering provides for the possibility of gathering information on the static and dynamic properties of the solitons and allows for restoring of the magnetic momentum distribution in the solitons. We hope that such calculations will stimulate the formulation of a series of experiments where solitons can be experimentally observed. [Preview Abstract] |
|
K1.00230: THz imaging system with the IJJ emitter Manabu Tsujimoto, Hidetoshi Minami, Masashi Sawamura, Kaveh Delfanazari, Takashi Yamamoto, Takanari Kashiwagi, Kazuo Kadowaki The intrinsic Josephson junction (IJJ) emitter consisted of thousands of IJJs uniformly stacked in single crystalline high-$T_{c}$ superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ (Bi-2212) [L. Ozyuzer \textit{et al}., Science \textbf{318}, (2007) 1291.] is expected to be a novel source of the continuous terahertz electromagnetic waves (THz-waves). The maximum emission power of tens of microwatts recently obtained with the mesa structure of IJJs seems to be sufficient to make use of the IJJ emitter for some practical applications such as THz imaging. According to the cavity resonance condition, we can control the radiation frequency by changing the geometrical size of the mesa. In this study, we develop the THz imaging system with IJJ emitter. In the presentation, we will show some transparent images of standard specimens obtained by the raster scanning method. Also, we will mention some problems to be solved for the future applications of the IJJ emitter. [Preview Abstract] |
|
K1.00231: Front instabilities, confinement effect and fracture in drying colloidal nanoparticle Deeder Aurongzeb Drying colloidal suspension of oxide nanoparticle can fracture in fractal patterns. While similar in size TiO$_{2}$ and Al$_{2}$O$_{3}$ particles can fracture differently. We found that Alumina nanoparticle forms radially inward crack from the edge of the droplet or planer film like fluid while Titania nanoparticle form fractal cracks. Using polarized light we observe stress field formation during evaporation and crack growth. We find that crack direction is driven by surface tension rather than thermal energy of the suspended nanoparticle. Evaporation based nanoparticle assemble and effect of confinement and electric current will be also discussed. [Preview Abstract] |
|
K1.00232: High-Pressure Studies of Valence and Magnetic State in Europium Metal W. Bi, G. Fabbris, J. Schilling, N. Souza-Neto, D. Haskel, J. Zhao, E. Alp, Y. Meng, A. Alsmadi The strong local-moment magnetism in divalent Eu metal (4f$^{7}$) suppresses superconductivity. At extreme pressure Eu is expected to become trivalent and nonmagnetic (4f$^{6}$). Recently, superconductivity in Eu was discovered by Debessai \textit{et al}. for pressures above 80 GPa [1]. However, Eu's transition temperature lies near 2 K, nearly an order of magnitude lower than for comparable trivalent d-electron metals, possibly because Eu is not fully trivalent but rather mixed valent. Here we report recent experimental results on Eu's valence and magnetic state to Mbar pressures through synchrotron x-ray absorption near edge structure (XANES), synchrotron x-ray magnetic circular dichroism (XMCD), and synchrotron M\"{o}ssbauer spectroscopy (SMS).\\[4pt] [1] M. Debessai, T. Matsuoka, J. J. Hamlin, J. S. Schilling, and K. Shimizu, Phys. Rev. Lett. 102, 197002 (2009). [Preview Abstract] |
|
K1.00233: Hybrid Rings for circuit Quantum Electrodynamics E. Hoffmann, F. Deppe, T. Niemczyk, E. P. Menzel, G. Wild, H. Huebl, M. Mariantoni, A. Marx, R. Gross, T. Wirth, A. Lukashenko, A. Ustinov, A. P. Zhuravel Experiments in the field of circuit QED require detection schemes for microwave signals on the single photon level. In particular, devices acting as microwave beam splitters are necessary. Using Nb thin films on silicon and sapphire substrates, we fabricated superconducting $180^{\circ}$ microstrip hybrid rings acting as beam splitters with center frequencies of about $6$\,GHz. For the magnitude of the coupling and isolation we find $-3.5\pm 0.5$\,dB and at least $-15$\,dB, respectively, in a bandwidth of 2\,GHz. We also investigate the effect of reflections at the contact between the superconducting hybrid ring and the normal conducting wiring using low temperature laser scanning microscopy. Our measurements indicate that our hybrid rings are well suited for on-chip applications in circuit QED experiments. We acknowledge financial support by the DFG via SFB 631, as well as support by and CFN, EU project SOLID and the German Excellence Initiative via NIM. [Preview Abstract] |
|
K1.00234: Magnetic behaviors in Fe(Se,Te) system Hongliang Shi The magnetic behaviors in Fe(Se,Te) system are investigated systematically by using the density functional theory. Our results show that for FeSe and FeTe in their respective ground state with different magnetic configurations, the easy axis of magnetization does not have any obvious preference. As for FeSe$_{0.5}$Te$_ {0.5}$, in the collinear calculation only setting the values of magnetic moments, the ground state is in the ``double stripe'' magnetic phase; while the ``single stripe'' magnetic arrangement is found to be the ground state if the easy axis of magnetization is considered in our calculations. Our spiral calculations also successfully predict the commensurate (0.5, 0.5) ordering observed in FeSe$_{0.5}$Te$_{0.5}$ system experimentally. Furthermore, two incommensurate excitations near (0.5, 0.5) are also reproduced in the spin spiral states compared with the diagram of scattering plane obtained by neutron scattering. [Preview Abstract] |
|
K1.00235: Synthesis and superconductivity in Li-Fe-As-N H.H. Sung, K.J. Syu, S.C. Chen, W.H. Lee The preparation of LiFeAs compound either in polycrystal or single crystal form is difficult to handle due to its reactivity with air and sensitivity to moisture of lithium. In this report we use Li$_{3}$N, Fe and As as starting materials. During the heating process, no high pressure, no Ta, Nb or W tube, is required to synthesize the polycrystalline sample. The crystallographic data and superconducting transition temperature (T$_{c})$ of the samples as prepared have been investigated through powder x-ray diffraction, magnetization and electrical-resistivity measurements. Discussion will be directed toward the influence of N on the superconductivity in Li-Fe-As from the viewpoint of pinning or substitute effect. [Preview Abstract] |
|
K1.00236: Evidence for intrinsic vortex pinning in 1111 Fe arsenides single-crystals Gang Li, Gael Grisonnanche, Benjamin Conner, Nikolai Zhigadlo, Sergiy Katrych, Zbigniew Bukowski, Janusz Karpinski, Luis Balicas We performed a study of the angular dependence of the magnetic torque $\tau(\theta)$ in LaFeAsO$_{0.9}$F$_{0.1}$ and in SmFeAsO$_{0.9}$F$_{0.1}$ single crystals. Here, $\theta$ is the angle between the magnetic field and inter-plane c-axis. As the temperature is lowered, one observes the emergence of sharp features in the magnetic torque for fields nearly aligned along the conducting planes. In particular, one observes two sharp peaks at a critical angle $\theta_c$ placed respectively slightly above and below $\theta = 90^{\circ}$, in the reversible component of the torque. Their position in angle, relative to $\theta =90^{\circ}$ , decreases as the field increases, and increases as the temperature is lowered. We conclude that $\theta_c$ corresponds to a critical pinning angle whose behavior is consistent with theoretical predictions for the intrinsic pinning of vortices by a layered crystallographic structure. However, in sharp contrast with the cuprates, in the region of temperatures where this behavior is observed the superconducting anisotropy of 1111 Fe arsenides is rather small, as measured by torque magnetometry. [Preview Abstract] |
|
K1.00237: Investigation of the role of spin-orbit coupling on transport properties of iron pnictide materials Sudhakar Pandey, Hiroshi Kontani, Dai Hirashima, Ryotaro Arita, Hideo Aoki A generic feature associated with the electronic structure of iron pnictides and chalcogenides, which are currently under intense investigation for their superconducting properties, is that the 3d orbitals of Fe make dominant contribution to density of states near the Fermi level. Incorporating this along with other realistic band features within a multiband tight-binding model, we investigate the role of atomic spin- orbit coupling associated with the 3d orbitals on the transport properties of these materials. Our investigation highlights the importance of some characteristic features associated with the electronic band, such as accidental degeneracy, Dirac cone, and orbital hybridization. we find significantly large spin Hall conductivity in the paramagnetic state that is comparable with Pt. We also find finite anomalous Hall conductivity in the ferromagnetic state. [Preview Abstract] |
|
K1.00238: Anisotropic structural and magnetic properties of the field-aligned superconducting system SmFeAsO$_{1-x}$F$_x$ ($x =$ 0.05, 0.1, 0.2, 0.25, and 0.3) Y.B. You, J.W. Wang, M.F. Tai, H.C. Ku, Y.Y. Hsu Anisotropic structural and magnetic properties of the field-aligned superconducting system SmFeAsO$_{1-x}$F$_x$ ($x =$ 0.05, 0.1, 0.2, 0.25, 0.3) are reported. Due to the Fe spin-orbital related anisotropic exchange coupling, all the tetragonal microcrystalline powders in epoxy were aligned at room temperature using the field-rotation method where the tetragonal $ab$-plane is parallel to the magnetic alignment field $B_a$ of 0.9 T and the $c$-axis parallels to the rotating axis. Anisotropic magnetic properties are studied through low temperature magnetic measurements along the $c$-axis and paralleled to the $ab$-plane of aligned samples in both ZFC and FC modes. The under-doped compound ($x =$ 0.1) is not superconducting with an antiferromagnetic N\'{e}el temperature $T_N \sim$ 40K, while the two optimum-doped compounds ($x =$ 0.2 and 0.25) show high superconducting transition temperatures $T_c$ of 49K and 50K, respectively. The variation of anisotropic structural and magnetic properties for this system are discussed and compared with the previously reported 52 K anisotropic superconductor Sm$_{0.95}$La$_{0.05}$FeAsO$_{0.85}$F$_{0.15}$. [Preview Abstract] |
|
K1.00239: COMPLEX STRUCTURED MATERIALS II |
|
K1.00240: The effects of asymmetric configurations on electronic properties of bilayer graphene nanoribbons Y. -C. Huang Low-energy electronic properties of bilayer graphene nanoribbons subject to the effects of asymmetric configurations are studied by using the tight-binding model. They are strongly dependent on the interlayer interactions, the ribbon edges, the ribbon width ($N_y$), and the upper ribbon displacement ($N_D$). The interlayer interactions significantly modify the energy dispersions, alter the subband spacing, change the subband curvature, produce the new edge state, and induce asymmetry of energy bands. There are partial flatbands at the Fermi level and one-dimensional parabolic bands at others. These make density of states (DOS) exhibit delta- function-like structure and asymmetric prominent peaks, respectively. Energies of the extra band-edge states can be tuned by varying the upper ribbon displacement. As $N_D$ grows from zero, the new edge states show a tendency to increase near low energy, while the curvature of the extra band-edge states display bold change about Fermi level $E_F$. The above- mentioned effects are completely reflected in the features of DOS, such as the generation of special structures, the shift of peak position, and the change in peak height. The predicted electronic properties could be examined by the experimental measurements on absorption spectra. [Preview Abstract] |
|
K1.00241: Kronig-Penney Model of Graphene in a Magnetic Field of Arbitrary Strength Norman Horing, Sina Bahrami We address the magneto-dynamics of a 2D graphene sheet with a one dimensional periodic array of quantum wires, using a Kronig-Penney type model. In particular we examine the role a normal magnetic field inducing Landau quantization effects in terms of a closed form integral representation involving only elementary functions which incorporates the full spectrum of magnetic-quantized graphene states and energies. [Preview Abstract] |
|
K1.00242: Effective Magnetic Fields in Graphene Superlattices Herbert Fertig, Jianmin Sun, Luis Brey We demonstrate that the electronic spectrum of graphene in a one-dimensional periodic potential will develop a Landau level spectrum when the potential magnitude varies slowly in space [1]. The effect is related to extra Dirac points generated by the potential whose positions are sensitive to its magnitude. We develop an effective theory that exploits a chiral symmetry in the Dirac Hamiltonian description with a superlattice potential, to show that the low energy theory contains an effective magnetic field. Numerical diagonalization of the Dirac equation confirms the presence of Landau levels. Possible consequences for transport are discussed. \\[4pt] [1] Jianmin Sun, H.A. Fertig, and L. Brey, Phys. Rev. Lett. {\bf 105}, 156801 (2010). [Preview Abstract] |
|
K1.00243: Graphene Energy Loss Spectroscopy for Perpendicular Particle Incidence Vassilios Fessatidis, Antonios Balassis, Norman J.M. Horing In this work we determine the energy loss of a fast charged particle probe moving perpendicular to a two-dimensional ($2D$) graphene sheet. The response dynamics of the $2D$ graphene sheet are modeled using the random phase approximation in the degenerate limit (zero temperature). We analyze the energy loss of the probe particle for normal incidence to the graphene sheet as a function of its velocity, examining contributions from both the particle-hole and plasmon excitations. [Preview Abstract] |
|
K1.00244: Ab initio Calculations of Geometric and Electronic Structure of Graphene-Au System Roberto Nunez-Gonzalez, Donald H. Galvan, Alvaro Posada-Amarillas Structural and electronic properties of graphene with one gold atom at top were calculated using the Full-Potential Augmented Plane Waves with Local Orbitals Method and the local density approximation (LDA), within the Density Functional Theory. For the calculations, we use a 3x3x1 supercell of graphene, calculating the stability of the system with the gold atom at three different sites: Hole, Bridge and Top sites. For each site, the atoms are relaxed minimizing forces. An analysis of the structural properties is performed for each site, calculating the density of states (DOS). A comparison with pure graphene is realized. [Preview Abstract] |
|
K1.00245: Geometric and Electronic structures of deformed bilayer graphenes Jen-Hsien Wong, Bi-Ru Wu, Ming-Fa Lin The electronic properties of bilayer AB-stacked graphene are investigated with a first-principles method when homogeneous and uniaxial strains are exerted. The two types of strains can be either tensile or compressive. The maximum deformation ratio is 36{\%} for tensile strain, and 20{\%} for compressive strain. The uniaxial strains along the armchair (A strain) or zigzag (Z strain) directions are considered. Bilayer AB-stacked graphene belongs to semimetal essentially. One pair of $\pi $ bands owns two intersections near the Fermi level. One intersection lies at K point; the other one is near K point along the path of $\Gamma $ to K. The $\pi $ band overlap is approximately 2.6meV. No gap will be developed for bilayer graphene under homogenous strain or A strain. Nevertheless, tensile Z strain results in a tiny indirect band gap near R point. [Preview Abstract] |
|
K1.00246: Magneto-electronic specific heat of graphene Shih-Yang Lin, Yen-Hung Ho, Ming-Fa Lin, Yuan-Cheng Huang The electronic specific heat related to the Landau levels of monolayer graphene is studied by the Peierls tight-binding model. The low-temperature thermal properties are dominated by the two low-lying Landau levels with the Zeeman splitting. They give rise to rich temperature and magnetic-field dependence. The T-dependent specific heat reveals the composite form of 1/T and exponential function. Also, a prominent peak appears in the T-dependent (B-dependent) spectrum with its critical temperature T$_{c}$ (critical magnetic field B$_{c})_{.}$ Moreover, there has a simple linear relationship between T$_{c }$and B$_{c}$. In a slightly doped graphene, there exists an extra shoulder structure in the specific heat. Such structure mainly comes from the Zeeman effect and temperature-dependent carrier distribution. [Preview Abstract] |
|
K1.00247: Electronic structure of a realistic model of amorphous graphene Vitaliy Kapko, Avishek Kumar, David Drabold, Michael Thorpe We calculate the electronic properties of a realistic atomistic model of amorphous graphene. The model contains odd-membered rings, particularly five and seven membered rings and no coordination defects.We show that odd-membered rings increase the electronic density of states at the Fermi level relative to crystalline graphene; a honeycomb lattice with semimetallic character. Some graphene samples contain amorphous regions, which even at small concentrations, may strongly affect many of the exotic properties of crystalline graphene, which arise because of the linear dispersion and semi-metallic character of perfectly crystalline graphene. Estimates are given for the density of states at the Fermi level using a tight-binding model for the $\pi$ states. We also report preliminary density functional results for the electronic structure. [Preview Abstract] |
|
K1.00248: Vibration analysis of Graphene embedded in ordered fluids using Raman spectroscopy Min Sang Park, Karthik Nayani, Jung Ok Park, Mohan Srinivasarao We studied the vibrational characteristics of both single- and multi-layered Graphene embedded in liquid crystal (LC), possessing various ordered phases, by polarized micro-Raman spectroscopy. The evolution of the vibrational modes (G and 2D bands) was studied in 8CB in the isotropic, nematic and smectic A phases. The shifts in the vibrational modes are discussed in the context of the phase transition in the LC system. [Preview Abstract] |
|
K1.00249: localization of plasmonic excitations in graphene induced by nanoscale potential Jung-Jung Su, Hari Dahal, Rodrigo Muniz, Stephan Haas, Alexander V. Balatsky The near-ballistic transport property at close to room temperature makes graphene a strong candidate for integrated nanoelectronic application. Graphene-based plasmonics is one of the devices proposed that integrate electronic and light transport. By utilizing localized plasmonic excitation, plasmonics can transport light with a sub-wavelength dimension. We report our calculation on plasmonic excitation induced by different local structures. The polarization obtained by random-phase-approximation (RPA) is diagonalized to extract plasmon modes. We have also studied the effect due to gating and due to tunning of local potential structure geometry. These prediction can be tested by scanning tunneling microscope and is important both in fundamental and in application aspects. [Preview Abstract] |
|
K1.00250: Adsorption of water on a carbon-gold surface Fernando Maga\~na, Gerardo J. Vazquez Density functional theory and molecular dynamics were used at 300 K to study first the interaction of a gold atom (Au) with a graphene layer with a vacancy. The Au Atom is adsorbed on the vacancy then we studied the adsorption of H$_{2}$O on the Au anchored on the vacancy of graphene. We found that the water molecule is adsorbed on such configuration and it is not even dissociated at high temperatures like 1000 K. [Preview Abstract] |
|
K1.00251: The interaction of mercury with halogenated graphene Abigail Kirchofer, Erdem Sasmaz, Jennifer Wilcox The interaction of mercury with halogenated graphene was studied using plane-wave density functional theory. Various configurations of H, Hg, O and Br or Cl on the zigzag edge sites of graphene were investigated. Although Hg-Br (or -Cl) complexes were found to be stable on the surface, the most stable configurations found were those with Hg adjacent to O. The surface atoms Hg, O, and Br tend to repel each other during geometric optimization, moving towards an H atom nearest-neighbor where possible. The strength of the Hg-graphene interaction is very sensitive to the local environment. The Hg-graphene binding energy is strongest when the Hg is located next to a surface O but not immediately next to a bound Br. DOS analysis revealed that Hg adsorption involves a gain in Hg 6 p-states and a loss in Hg 5 s electron density, resulting in an oxidized surface-bound Hg complex. DOS analysis suggests that Br strengthens the Hg-graphene interaction by modifying the surface carbon electron density; however, when Br is adjacent to Hg, a direct Hg-Br interaction weakens the Hg-C bond. These investigations provide insight into the mechanism associated with enhanced Hg adsorption on Br-functionalized carbon materials for Hg emissions reductions from coal-fired power plant applications. [Preview Abstract] |
|
K1.00252: Electric-field induced modification of Landau levels in graphene nanoribbon Hsien-Ching Chung, Yuan-Cheng Huang, Ming-Fa Lin The low energy magneto-ectronic properties of one-dimensional graphene nanoribbons are investigated by the Peierls tight-binding model with uniform magnetic and electric fields. They are mainly determined by the quantum confinement effects and the external fields. Magnetic fields result in the Landau levels (LLs), lead to the Landau wavefunctions, and enhance partial flat bands. Electric fields significantly modify the dispersionless LLs, change the band symmetry, induce more band-edge states, split the partial flat bands, and drastically alter the distribution of wavefunctions. The density of states directly reflects the main features of energy bands, such as the numbers, frequencies, heights and divergence forms of prominent peaks, which can be confirmed experimentally. The magneto-optical absorption spectra are predicted to be dramatically changed under the influence of external electric fields. [Preview Abstract] |
|
K1.00253: Spin-polarized energy gap opening in asymmetric bilayer graphene nanoribbons Gyubong Kim, Seung-Hoon Jhi Electronic and magnetic properties of bilayer zigzag graphene nanoribbon (bZGNR) are studied with the use of pseudopotential density functional method. The edge atoms in the top and bottom layers of bZGNR make a weak hybridization, which leads to band dispersion and magnetization different from monolayer ZGNR. For asymmetric bZGNR, where the top and bottom layers have different width, one edge is pinched by the interlayer bonding and the other edge sustains anti-ferromagnetic spin polarization. A small amount of charge transfer occurs from narrower to wider layer, and the band structure for each spin near the Fermi level exhibits an asymmetry. External electric field perpendicular to asymmetric bZGNR produces different energy-gap opening for each spin component, inducing half- metallicity. [Preview Abstract] |
|
K1.00254: Synthesis and Characterization of Graphene Sheets Covalently Functionalized with Polyaniline Sanjeev Manohar, Srikanthrao Agnihotra, Akshay Phulgirkar Herein we report covalent functionalization of graphene oxide (GO) with conducting polymer polyaniline and aniline tetramer for the first time. The covalently functionalized rGO is electrically conducting, shows improved electrochemical properties and enhanced specific capacitance compared to rGO. We also observed enhanced thermal stability and antistatic properties can be obtained on addition of these covalently functionalized composites into the polymer matrix such as PMMA. [Preview Abstract] |
|
K1.00255: Thermoelectric Power in Dual-Gated Bilayer Graphene Chang-Ran Wang, Vincent Lu, Wei-Li Lee We have performed thermoelectric transport measurements of dual-gated bilayer graphene device. The thermopower reached a maximum value of $\vert $Sm$\vert $ when tuning its carrier density by gates. The $\vert $Sm$\vert $ was found to monotonically increase with displacement field D introduced through the top and bottom gates. At 100K, $\vert $Sm$\vert $ attains a value of $\sim $ 110 uV/K at D $\sim $ 1V/nm, which is nearly two-fold larger than that at D = 0. The detailed temperature-dependence of Sm and comparison to the resistivity data will be presented. [Preview Abstract] |
|
K1.00256: Trigonal Distortion of Valley Current in Bilayer Graphene Patricio Vargas, Alvaro Nu\~nez, Eric Suarez Bilayer Graphene (BLG) is extensively explored due to its remarkably electronic properties. Its band structure has two inequivalent but degenerate points K and K' at the corners of the Brillouin Zone, because their large separation there have been proposition to use a valley index, or pseudospin to generate valley dependent currents. In BLG these currents can be created by applying an step like bias, the topology of BLG in the two zones leads to the formation of a 1D chiral zero modes transverse to the applied bias. There are two such modes per spin per valley and the current have opposite direction in each valley. We explore how the trigonal warping of BLG affects these modes. Breaking the symmetry of the unit cell in BLG opens a gap, the shape of the Berry Curvature depends of the bias applied, for very low bias (few meV) the topological charge breaks in four well defined peaks, three having the same sign and magnitude and the fourth with opposite value, the overall charge remains unaltered, these fraction charges lead to a distortion of the chiral zero modes. We calculate the currents and show how the system evolves by tuning the effect of the trigonal warping. [Preview Abstract] |
|
K1.00257: A Way from GHz to THz Graphene Nanosensor Yuichi Ochiai, Akram Mahjoub, Nobuyuki Aoki, Jung Woo Song, Gregory Aizin, Jonathan Bird, David Ferry, Yukio Kawano, Koji Ishibashi The unique bandstructure, and associated carrier properties, of graphene make this material of ideal interest for application as a broadly tuneable sensor, for specific application to the microwave and terahertz (THz) regime. The gapless spectrum characteristic of single-layer graphene, as well as the small forbidden gap that appears in bilayer graphene, is ideally matched to the low (meV) energy of photons near the THz regime, in marked contrast to conventional semiconductors whose relevant bandgaps are typically several orders of magnitude larger. In this presentation, we describe the results of ongoing research that is being undertaken with the objective of developing upto THz nanosensors based on graphene. We describe the preparation of graphene devices by mechanical exfoliation, after which we discuss the characterization of their electrical properties using low-temperature magneto-transport investigations [1]. These studies demonstrate the formation of open quantum-dot structures in small graphene flakes, contacted by sub-micron scale metal electrodes. The observation of quantum fluctuations in the magneto-resistance of these structures indicates the presence of quantized dot states, whose characteristics may be of use in THz sensing. [1] Y. Ujiie et al., J. Phys.: Condens. Matt. 21 (2009) 382202. [Preview Abstract] |
|
K1.00258: Photoluminescence from hydrogenated graphene Volodymyr Turkowski, Talat S. Rahman We consider the optical properties of hydrogenated graphene as a function of hydrogen concentration between the graphene and graphane limits. In particular, we show that with increasing hydrogen concentration the gap in the electron density of states grows from 0 to approximately 5eV in the case of graphane. For intermediate concentrations, additional electronic states with energies smaller than 5eV appear. These states make the system optically active in the visible range. We pay special attention to the possibility of ultrafast photoluminescence in the system for different values of hydrogen concentration and hole doping. For example, for excitations by ultrafast laser pulses, the system demonstrates significant visible range photoluminescence driven by the electron-phonon interaction. In the case of graphane, the effect can be significantly enhanced by hole doping, when the phonon spectrum demonstrates a Kohn anomaly, which results in a faster partial equilibration between the electrons and an optical phonon subsystem. [Preview Abstract] |
|
K1.00259: Controllable p-n Junction Formation in Monolayer Graphene Using Electrostatic Substrate Engineering Hsin-Ying Chiu, Vasili Perebeinos, Yu-Ming Lin, Phaedon Avouris The p-n junction is the basic element of modern electronics, providing the non-linear response essential for rectifying and switching currents. In conventional semiconductors, p-n junctions are produced by inserting donor and acceptor atoms in the crystal lattice. This approach, however, fails to produce effective results in nanoscale or low-dimensional electronic materials, such as graphene. Graphene itself is attracting much attention due to its unique electronic properties. In addition to having outstanding carrier mobilities graphene offers opportunities extending beyond CMOS technology, such as p-n junction electron (Veselago) lenses. Thus, graphene electronics depends on the ability to fabricate high-quality p-n junctions. Doping of graphene has been previously achieved by using multiple electrostatic gates, or charge transfer from adsorbants. Here we demonstrate a novel approach to create p-n junctions by changing the local electrostatic potential in the vicinity of one of the contacts without the use of extra gates. It is based on the electronic modification of the substrate and produces a well-behaved, sharp junction whose position and height can be controlled. [Preview Abstract] |
|
K1.00260: Opto-Electronic Properties of Nano-Structured Graphitic Carbon Measured Using Micro-Raman Spectroscopy Logan Scheel, Kevin Mead, Jeffery Demers, Jeff Simpson Nano-structured graphitic carbon allotropes offer promise for next generation optical and electronic devices. Graphene, a single atom layer of hexagonally arranged carbon atoms, is particularly interesting as the basis for other forms of graphitic carbon, e.g., single-wall carbon nanotubes (SWCNTs). The unique linear energy versus momentum band structure of graphene leads to interesting fundamental physics and potential device applications. We report on the design and implementation of a micro-Raman spectroscopy system used to measure the opto-electronic properties of graphene and SWCNTs. Using mechanical exfoliation, single and multilayer graphene flakes are deposited on Si/SiO$_{2}$ substrates. Our Raman system consists of multiple laser sources including, HeNe, Argon, and dye lasers, which provide excitation light to samples mounted in an optical microscope. Inelastically scattered light is collected and directed to a grating spectrometer with CCD detection. Analysis of the Raman spectra reveal specific phonons known as the D, G, G'$_{2D}$ modes common to graphitic carbon. We fit the modes with Lorentzians in order to quantify the layer number and analyze electron-phonon coupling. [Preview Abstract] |
|
K1.00261: Comparing the Inner and Outer Double-resonance Raman Scattering Processes in Bilayer Graphene Daniela Mafra, Elie Moujaes, Ricardo Nunes, Steven Doorn, Han Htoon, Marcos Pimenta The Raman spectroscopy has been widely used to study carbon materials. In this work the dispersion of phonons and the electronic structure of graphene systems can be obtained experimentally from the double-resonance (DR) Raman features by varying the excitation laser energy. The electronic structure was analyzed in the framework of the Slonczewski-Weiss-McClure (SWM) model, considering both the outer and inner DR process and the SWM parameters was obtained for each model. We show that the parameters obtained when we consider the inner DR process are in better agreement with those obtained from other experimental techniques, despite the fact that several previous studies about the DR process in graphene usually pay atention solely to the one-dimensional outer (DR) process. This result possibly shows that there is still a fundamental open question concerning the double resonance process in graphene systems. [Preview Abstract] |
|
K1.00262: A search for the dominant heat conducting phonon modes in graphene: An atomistic simulation study Hengji Zhang, Kyeongjae Cho We have performed an equilibrium molecular dynamic (MD) simulation study to investigate phonon thermal transport in graphene at 300K with Green-Kubo method. Using a newly optimized reactive empirical bond order carbon potential (Lindsay, et al. Physical Review B 81, 205441, 2010), our calculated thermal conductivity (TC) of defect free graphene is about 3000 W/mK in good agreement with experiments($\sim $3000-5000 W/mK). A maximum of $\sim $1000 fold reduction in TC is possible to achieve for graphene with defects and surrounding viscous medium. As we decompose the in-plane and out-plane phonon vibration modes of graphene in MD simulations, the out of plane vibration modes (ZA phonon) contribute to about 50{\%} of the overall TC. This large contribution from ZA modes is explained with density of states analysis. We have clarified a recent controversy on which polarization mode in graphene is the main heat carrier. [Preview Abstract] |
|
K1.00263: Polarized Nonresonant Raman Spectra of Graphene Nanoribbons Guangfu Luo, Jing Lu, Lu Wang, Lin Lai, Jing Zhou, Rui Qin, Hong Li, Zhengxiang Gao, Wai-Ning Mei We study the non-resonant Raman scattering of armchair- and zigzag-edged graphene nanoribbons using density functional perturbation theory. We find that in both types of nanoribbon, the Raman spectrum is extremely polarized along the ribbon length direction, over 102 times larger than those of the other orientations. Also we discover that the scattering intensity of this major polarization exhibits conspicuous quantum oscillation with the ribbon width in armchair-edged nanoribbons. While in zigzag-edged nanoribbons, the Raman spectra shows relatively weak dependence on the ribbon width. We propose employing the surface-enhanced Raman spectroscopy to detect these features, a procedure which has been applied in the studies of graphene. [Preview Abstract] |
|
K1.00264: A broadband microwave study of CVD grown graphene Wei Liu, Carl Magnuson, Yufeng Hao, Rodney Ruoff, Peter Armitage We apply a broadband microwave Corbino spectrometer to study the complex conductivity of CVD grown graphene deposited on a high resistivity Si substrate. Explicit frequency dependency of the complex conductivity are obtained down to 300 mK and in a frequency range from 100 MHz to 20 GHz. We compare our data to the low frequency limit of the conductance of different theoretical models and make connection to other experimental results. We will also report measurements of the conductivity using time domain terahertz spectroscopy. [Preview Abstract] |
|
K1.00265: Graphene grown on Ni surface: quantitative analysis Irma Kuljanishvili, Dmitriy Dikin, Alice Riley, Pavan Patel, Venkat Chandrasekhar CVD growth of graphene on various substrates, e.g. Copper or Nickel, has become an increasingly popular method for production of large films. Unlike copper mediated growth, the CVD growth process of graphene on Nickel film is not self-limiting, hence understanding the main factors and/or conditions that influence the growth of one or few layers of graphene on Nickel is important. We will present our results on CVD growth of graphene on Nickel films deposited on Si/SO2 substrates. We will discuss our results of single and few layer graphene synthesis and our attempts to explain the growth mechanism of graphene. Correlation between SEM and AFM/EFM studies and optical characterization of graphene will be presented. A.R. acknowledges the support of International Institute of Nanotechnology REU Program [Preview Abstract] |
|
K1.00266: Experimentally determined optical-properties of monodisperse graphene quantum dots with controlled size and geometry Vikas Berry, Nihar Mohanty, Ashvin Nagaraja In this talk, we will present a novel route for high throughput production of monodisperse GQDs with controlled spatial dimensions (5 nm - 100 nm at 1 nm resolution) and geometry (squares, rectangles, and triangles). We would show the first detailed experimental demonstration of the GQD optoelectronic-property-tuning via tailoring of their spatial dimensions and geometry. Further, we would be presenting the detailed structural, optical and electronic characterization of the as-obtained GQDs via various microscopic and spectroscopic techniques. While the top down methods of fabrication including lithography-based methods or sonochemical methods are either extremely low throughput or have limited control on GQDs' dimensions and geometry; the bottom-up fabrication methods are limited by the achievable size ($<$ 3 nm). [Preview Abstract] |
|
K1.00267: Magneto-transport of graphene quantum dots Kuei-Lin Chiu, Charles Smith, Malcolm Connolly, Simon Chorley, Jonathan Griffiths Graphene nanostructures continue to attract attention due to their customizable electronic properties and compatability with existing semiconductor device processing. The promise of long spin relaxation times makes graphene quantum dots – small islands of confined charge - particularly suited to quantum computing architectures that manipulate the spin degree of freedom. In order to probe the spin and charge dynamics of geometrically confined Dirac quasiparticles, we have performed magneto-transport measurements on a single dot and a series-coupled double dot at temperatures down to 100 mK and magnetic fields up to 12 T. In the single dot structure we follow the energy required to add electrons to the dot in the many-electron regime. The energy levels show a rich structure of ``kinks'' as a function of the magnetic field, and we analyze this result in terms of Landau level formation in the quantum dot. In the double quantum dot structure we find that the conductance of the device as a function of the energy levels in the dots exhibits the typical honeycomb pattern. From the dimensions of the honeycomb we extract the capacitive coupling strength between dots and the gates, and examine how this evolves as a function of magnetic field. We analyze this result in terms of magnetic field induced changes in the capacitive coupling between the quantum dot and the plunger-gates. [Preview Abstract] |
|
K1.00268: Impurity and phonon scattering in silicon nanowires W. Zhang, M.P. Persson, H. Mera, C. Delerue, Y.M. Niquet, G. Allan, E. Wang We model the scattering of electrons by phonons and dopant impurities in ultimate [110]-oriented gate-all-around silicon nanowires with an atomistic valence force field and tight-binding approach. All electron-phonons interactions are included. We show that impurity scattering can reduce with decreasing nanowire diameter due to the enhanced screening by the gate. Donors and acceptors however perform very differently : acceptors behave as tunnel barriers for the electrons, while donors behave as quantum wells which introduce Fano resonances in the conductance. As a consequence the acceptors are much more limiting the mobility than the donors. The resistances of single acceptors are also very dependent on their radial position in the nanowire, which might be a significant source of variability in ultimate silicon nanowire devices. Concerning phonons, we show that, as a result of strong confinement, i) electrons couple to a wide and complex distribution of phonons modes, and ii) the mobility has a non-monotonic variation with wire diameter and is strongly reduced with respect to bulk. French National Research Agency ANR project QUANTAMONDE Contract No. ANR-07-NANO-023-02 and by the D\'el\'egation G\'en\'erale pour l'Armement, French Ministry of Defense under Grant No. 2008.34.0031. [Preview Abstract] |
|
K1.00269: ARTIFICIALLY STRUCTURED MATERIALS |
|
K1.00270: Spin splitter in a quantum ring with Rashba coupling B. Tanatar, V. Moldoveanu We use non-equilibrium Greens' function formalism to calculate the spin currents in a one-dimensional ring coupled to three leads in the presence of perpendicular magnetic flux $F$ and Rashba spin-orbit coupling. A finite bias is applied between the input lead and the other two output leads. We demonstrate that the spin-orbit coupling allows one to operate this system as a spin splitter, i.e. the output leads deliver spin-polarized currents with different orientations. We find that the spin splitter operation can be tuned at integer multiples of $F/F_0$. Efficiency depends not only on the value of the Rashba coupling but also on the bias applied between the input and output leads. The selected spin orientation of the output leads can be reversed by a slight change of their contact position. We also discuss the connection between the spin splitter operation and the spectral properties of the ring. [Preview Abstract] |
|
K1.00271: Nanoscale engineering of photoelectron kinetics in quantum dot structures Andrei Sergeev, Vladimir Mitin, Nizami Vagidov We investigate photoelectron kinetics in advanced quantum dot (QD) structures, which combine quantum tuning of localized and conducting states with controllable photoelectron properties. Our unique approach is based on engineering of photoelectron capture processes using various configurations of manageable potential barriers around single QDs and collective barriers around QD planes (lateral structures) and QD clusters (vertical structures). Potential barriers around QDs are formed by electrons bounded in dots and ionized impurities in the depletion region. These potential barriers separate the conducting electron states from the localized intra-dot states. Besides manageable photoelectron lifetime, the novel structures will also provide high scalability, low generation-recombination noise in sensing applications and low recombination losses in QD solar cells. [Preview Abstract] |
|
K1.00272: Long-range exciton-exciton interactions in metal-semiconductor hybrid structures Anshu Pandey, Hsinhan Tsai, Hsing-lin Wang, Jeffrey M. Pietryga, Victor I. Klimov Establishment of long-range communication between semiconductor nanocrystals (NCs) is an important step towards their use in real-life devices. Most research towards enhancing inter-NC coupling has followed two strategies: attempts to enhance charge transfer rates in NC assemblies, and enhancement and control of energy transport via exciton transfer. We have explored the second strategy for obtaining strong coupling between distant NCs. For this purpose, we have studied the optical properties of colloidal NCs tethered to spherical gold particles coated with a silica shell. These structures exhibited clear signatures of long range coupling between the NCs which manifested in the form of cooperative decay of excitons separated by large distances (up to 40 nm apart). We further show that this coupling does not alter the overall emission efficiency of the excitons, though it significantly modifies emission rates. The observation of this regime of exciton interaction has potential applications in existing NC based devices such as lasers, and may also lead to novel applications that involve defect-tolerant energy transfer between distant chromophores [Preview Abstract] |
|
K1.00273: How to select quantum dots with smallest fine structure splitting under uniaxial stress for entangled photon sources Ming Gong, Weiwei Zhang, Guangcan Guo, Lixin He We propose a microscopic theory to build an exact relationship between the fine structure splitting (FSS) of exciton, the polarization of the emission lines and the amount of asymmetry in self-assembled quantum dots (QDs). Based on our model, strategy to select QDs with smallest FSS from large amount of QDs is proposed. The predilection in this work is supported by million atom empirical pseudo-potential calculation. Our theory can greatly simply the method to generate entangled photon sources using single QD. [Preview Abstract] |
|
K1.00274: Tunable Optical Switching/Routing by Negative Refraction in Liquid Crystal filled Opal and Inverted Opal Photonic Crystals Rabia Moussa, Ryotaro Ozaki, A. Efros, Anvar Zakhidov In this study, we investigate the optical characteristics and negative index of liquid crystal (LC) infiltrated inverse opal as a 3D photonic crystal (PC). We demonstrate that it is possible to achieve a tunable negative, by infiltrating LC into porous synthetic opal and inverted opal type PC. Using the optical anisotropy of LC and field sensitivity, the optical properties of porous PC infiltrated with LC can be easily controlled. The design of a simple and efficient wide angle optical switch/router is considered. Changing the electric field across the LC-PC, with the use of transparent electrodes, the refractive index of Opal-PC can be modulated within several percent, shifting the light beam between photonic bands with negative and positive dispersion. The calculations reveal that LC molecular orientation in the inverse opal strongly influences light propagation in 3D PC. [Preview Abstract] |
|
K1.00275: Analysis of Self-Assembled Monolayers in Nanoscale Switching Elements Matthew Roberson, Lam Yu Molecular junctions consisting of gold and silver electrodes and a self-assembled monolayer (SAM) have been shown to act as voltage-controlled electrical two-state switches due to the electrochemical migration of silver ions. In these junctions the SAM is sandwiched between the two metal electrodes. When a certain bias voltage is applied across the metal electrodes, atoms on the silver electrode surface are electrochemically oxidized, and the resulting silver ions are drawn by the local electric field toward the gold electrode. Upon deposition onto the gold electrode the silver ions are reduced to silver atoms. As more silver atoms are deposited onto the gold electrode, a metallic connection is formed between the electrodes resulting in a closed-circuit state between the two electrodes. The silver metallic bridges are metastable in these junctions, and they are dissolved when the voltage between the electrodes is swept back toward zero volts. When the silver filaments retract, the switch returns to an open-circuit state. Varying the functional group of the SAMs induces different switching characteristics in the junctions. We are analyzing the transition voltages at which this switching occurs for different SAMs under different temperature and humidity, and plotting the data to observe trends in order to isolate the key factors involved in this switching. [Preview Abstract] |
|
K1.00276: ABSTRACT WITHDRAWN |
|
K1.00277: High frequency shot noise measurements through a low temperature mechanical break junction Leland Richardson, Patrick Wheeler, Doug Natelson The systematic measurement of shot noise allows one to directly measure the transmittance of individual conductance modes, and can lead to useful inferences on the nature of quantum transport in various materials. At low temperatures (4.2 K) the contribution of heating-induced Johnson noise is reduced significantly; however, high-frequency lock-in detection techniques are used to further amplify the relative contribution of shot noise compared to Johnson noise. We have designed and built a cryogenic mechanical break-junction system with sufficient spatial resolution and minimal electronic background noise to perform such measurements. Geometrically, a reduction factor of $10^{-6}$ in spatial resolution is obtained from the gap spacing to the movement of the mechanical arm. An additional axial-to-linear reduction is gained from gearing, leading to an overall theoretical spatial precision between the electrodes on the order of $10^{-12}$ meters per revolution of the stepper motor powering the arm, providing sufficient precision to perform measurements on single atomic point contacts and molecules. Using this setup, quantum shot noise suppression at integral values of $G_0$ has been measured on Au junctions demonstrating the effectiveness of the device. [Preview Abstract] |
|
K1.00278: Angle- and position-resolved plasmon coupling in gold nanocrystal dimers Lei Shao, Jianfang Wang Interactions between the localized plasmons of metal nanocrystals have attracted much attention, because of their applications ranging from photonic devices to biomolecular detection. Gold nanorods (NRs) exhibit both the transverse and longitudinal plasmon modes, with the latter being strongly polarization-dependent. We have studied the coupling in Au NR homodimers and Au NR-Au nanosphere (NS) heterodimers. Experimental observations, as well as simulations, have revealed a number of interesting phenomena in the plasmon coupling. First, both the antibonding and bonding modes are existent in the NR dimer system and their intensity ratio decreases exponentially as the NR angle increases. Second, the NR-NS heterodimers exhibit Fano resonance properties and a NS-site-dependent coupling behavior. We believe that our results will be useful for developing complex plasmon-based photonic devices and ultrasensitive plasmonic sensors. The NR-based dimers can also potentially function as building blocks for the construction of metamaterials. [Preview Abstract] |
|
K1.00279: Strain Effects in Thermoelectric Ca$_{3}$Co$_{4}$O$_{9}$ Thin Films Robert Klie, Qiao Qiao, Ahmet Gulec, Tadas Paulauskas, Stanislaw Kolesnik, Bogdan Dabrowski, Cihat Boyraz, Mehmet Ozdemir, Dipanjan Mazumdar, Arun Gupta Thermoelectric oxides have attracted increasing attention due to their high thermal power and temperature stability. In particular, Ca$_{3}$Co$_{4}$O$_{9 }$(CCO), a misfit layered structure consisting of single layer hole-doped CoO$_{2}$ sandwiched between insulating Ca$_{2}$CoO$_{3}$ rocksalt layers, exhibits a high Seebeck coefficient at 1000 K.$^{ }$It was suggested that the Seebeck-coefficient can be further increased by growing doped thin films with controlled defects structures. This study combines pulsed layer deposition thin film synthesis of pristine CCO on several oxide substrates, as well as CCO thin films doped with Ti, Bi or La, with aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy (EELS) to examine the effects of interfacial strain and doping on the atomic and electronic structures of CCO. The thermoelectric properties will be measured and correlated to the local changes in the atomic and electronic structures. We will further evaluate the role of CoO$_{2}$ stacking faults, as well as film thickness on the thermoelectric properties of CCO. [Preview Abstract] |
|
K1.00280: First principle investigation of ZrO$_2$-CeO$_2$ heterojunction properties Marco Fronzi, Alessandro De Vita, Yoshitaka Tateyama, Enrico Traversa Here we present a computational Density Functional Theory approach to analyze the structural and electronic properties of the (100) and (111) ZrO$_2$-CeO$_2$ interface. Optimization of the lattice geometry for the separate ZrO$_2$ and CeO$_2$ bulks as well as the interface is carried out and the structural morphology is analyzed. The energy formation of the oxygen vacancies are analyzed at different values of lattice parameter, in order to verify its dependency on the strain. Activation energy of the oxygen migration are also calculated in the bulk as well as at the interfaces level. The effect of the doping on the lattice geometry is analyzed for the (111) and (100) interfaces in order to verify its influence on the morphologic disorder. [Preview Abstract] |
|
K1.00281: Structure, Vibrational Dynamics and Thermodynamics of silver thin-films on Cu(100) Samuel Roberts, James Westover, Abdelkader Kara We use a Real Space Green's function and the embedded atom method for interaction potentials, to examine the structural and vibrational properties of a silver thin-film (from one to four monolayers) on Cu(100). Due to the lattice mismatch, the first several layers of the substrate had major structural modification, in the form of buckling about 0.6A for the top two layers and 0.05A in the 6$^{th}$ layer. For the case of a mono-layer, the vibrational densities of state of the silver atoms extend substantially beyond the maximum of the bulk density. The atoms in the first copper layer's density of state also show substantial enhancement of the high frequency end. These reflect the strong bonding between the monolayer and the substrate. The vibrational thermodynamic functions for these interface atoms will be presented [Preview Abstract] |
|
K1.00282: Improvements in 3-omega measurement of thermal conductivity for nanostructured materials Chuanle Zhou, M. Grayson, G. Koblmueller Nanostructured materials have reduced thermal conductivity in order to enhance the thermoelectric figure of merit (ZT). The 3$\omega$ method is widely used for vertical thermal conductivity measurements in the nanostructure materials, especially layered materials. The challenge for this method is to measure the small 3$\omega$ voltage at the third harmonic, above the comparably large $\omega$ voltage from the sample at the fundamental frequency, complicated by the nonlinear signal from other components in the measurement circuit. We carefully study the 3$\omega$ method [Cahill, Rev. Sci. lnstrum. 61 (2), 802 (1990)] and develop a strategy to increase the signal to noise ratio of the data, for more accurate results. We also investigate an alternate sample preparation geometry for the 3$\omega$ measurement, so that the heat flow is vertical and linear through the thin film instead of cylindrical as is standard for this method. This results in a direct measurement of the vertical thermal conductivity in such an anisotropic material. New geometries for measuring lateral thermal conductivity will also be proposed and explored. [Preview Abstract] |
|
K1.00283: PHASE TRANSITIONS AND STRONGLY CORRELATED SYSTEMS |
|
K1.00284: Magnetic Superstructure and Metal-Insulator Transition in Mn-Substituted Sr$_3$Ru$_2$O$_7$ M.A. Hossain, Z.H. Zhu, B. Bohnenbuck, Y.-D. Chuang, Y. Yoshida, Z. Hussain, B. Keimer, I.S. Elfimov, G.A. Sawatzky, A. Damascelli We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr$_3$(Ru$_{1-x}$Mn$_x$)$_2$O$_7$, performed at both Ru and Mn $L$-edges. Resonant magnetic superstructure reflections together with ab-initio density functional theory calculations identify the ground state as a spin checkerboard with blocks of 4 spins up and 4 spins down. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low $x\sim 0.05$ Mn substitution. Perhaps more important, our results suggest that the same checkerboard instability might be present already in the parent compound Sr$_3$Ru$_2$O$_7$. In collaboration with: A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley) I. Zegkinoglou, M.W. Haverkort (MPI) J. Geck, D.G. Hawthorn (UBC) R. Mathieu, Y. Tokura, S. Satow, H. Takagi (Tokyo) H.-H. Wu and C. Schussler-Langeheine (Cologne). [Preview Abstract] |
|
K1.00285: Ultrafast quasiparticle dynamics in the hidden order state of URu$_{2}$Si$_{2}$ Mengkun Liu, Dzmitry Yarotski, Tomasz Durakiewicz, Stuart Trugman, Richard Averitt, Antoinette Taylor The heavy-fermion compound URu$_{2}$Si$_{2}$ has attracted much interest in the past two decades due to appearance of the 'hidden order' (HO) state in this material below 17.5 K. Despite an extensive effort, the development of the theoretical description of the origin of HO has been hindered by the lack of adequate experimental evidence regarding low-energy electronic structure of this compound. We report on application of ultrafast optical spectroscopy to probe quasiparticle dynamics in the vicinity of E$_{F}$ in a single crystal URu$_{2}$Si$_{2}$ undergoing the HO phase transition. The relaxation dynamics of the photoexcited carriers exhibits a strong dependence on temperature and excitation intensity. Data analysis using the Rothwarf-Talyor model demonstrates an opening of a 5 meV energy gap as the temperature decreases below 20 K. This behavior is consistent with recent results obtained from angle-resolved photoemission spectroscopy, scanning tunneling microscopy and neutron scattering experiments. [Preview Abstract] |
|
K1.00286: High Field (H,T) Phase Diagram and Anisotropy of CeRhIn$_{5}$ single crystals Yoshimitsu Kohama, Huiqiu Yuan, Lin Jiao, Marcelo Jaime, Fedor Balakirev, Eric Bauer The specific heat ($C_{p})$ of a single crystal sample of composition CeRhIn$_{5}$ was measured as a function of temperature and magnetic field applied perpendicular and parallel to the crystallographic $c-$axis. Our experiments, carried out at temperatures below the AFM ordering temperature $T_{N}$ = 3.7 K, show a clear anomaly in $C_{p}(H)$ when the applied field is strong enough to suppress the magnetic order. This anomaly, which reduces the magnitude as the temperature is lowered, was used to map the ($H,T)$ phase diagram for the first time to a magnetic field of 55 T and temperatures as low as 700mK.\footnote{Y. Kohama, C. Marcenat, T. Klein, and M. Jaime, \textit{Rev. Sci. Instrum}., \textbf{81}, 104902 (2010).} Extrapolation of the low temperature phase boundary indicates the presence of a magnetic field-induced quantum critical point at $H_{c} \approx$ 50 T that is weakly dependent of the sample orientation, although intermediate magnetic fields reveal clear anisotropy. Our results will be discussed in the context of field-induced quantum phase transitions in strongly anisotropic correlated matter. [Preview Abstract] |
|
K1.00287: Transport properties in magnetic Griffiths phases David Nozadze, Thomas Vojta We study the temperature dependence of the electrical resistivity in the quantum Griffiths phases associated with the ferromagnetic and antiferromagnetic quantum phase transitions in itinerate systems. The resistivity is calculated by means of the semi-classical Boltzmann equation. We show that the contribution to the resistivity due to the scattering by spin-fluctuations in rare regions varies as $T^{\lambda}$ with the logarithmic correction for both ferromagnetic and antiferromagnetic systems. Here $\lambda$ is the usual Griffiths exponent which takes the value $0$ at the critical point and increases with the distance from the criticality. We also consider other transport properties such as thermal resistivity, thermopower and Peltier coefficient. [Preview Abstract] |
|
K1.00288: Evolution of Power-Law Behavior of Temperature Dependence of Electrical Resistivity in Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ P.-C. Ho, R.E. Baumbach, A.A. Dooraghi, M.B. Maple, T. Yanagisawa The study of the Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ series has been carried out in order to investigate the effect of ferromagnetism (FM) on the unconventional superconductivity (SC), the high field ordered phase (HFOP), and quantum critical behavior in PrOs$_4$Sb$_{12}$ [1, 2, 3]. Two critical concentrations x$_{\rm{cr,1}} \sim 0.58$ and x$_{\rm{cr,2}} \sim 0.33$ were previously identified in this system [2]: SC disappears near x$_{\rm{cr,1}}$ and weak FM extends into the SC region for $x_{\rm{cr,2}}< x < x_{\rm{cr,1}}$ [3]. In order to further examine the possible quantum critical behavior, a power-law analysis of the temperature dependence of the electrical resistivity data is performed. Upon suppression of SC, for samples of $x_{\rm{cr,2}}< x < x_{\rm{cr,1}}$, the power-law exponent decreases from $\sim$ 1.8 toward 1 in the temperature region below 2.5\,K, resembling non-Fermi liquid behavior. \\[4pt] [1] Ho, et. al., Physica B 403, 1038 (2008).\\[0pt] [2] Ho, et. al., arXiv:1008.5198v1 (2010).\\[0pt] [3] Ho, et. al., 2010 APS March Meeting, A38.00005 (2010). [Preview Abstract] |
|
K1.00289: Temperature Dependent Investigations on Single Crystal Gallium Ferrite Using X-ray Diffraction and Raman Spectroscopy S. Mukherjee, Rajeev Gupta, Ashish Garg Ga$_{2-x}$Fe$_{x}$O$_{3}$ (0.8$\le $x$\le $1.2) or GFO is a room temperature paramagnetic piezoelectric material with its ferrimagnetic to paramagnetic transition temperature (T$_{c})$, varying from 200 K to 300 K. We synthesized GFO (x $\sim $ 1.08-1.10) single crystals using flux growth method. Partial occupancies of the cationic sites obtained using Reitveld refinement of XRD data were used to calculate the lattice magnetic moment. We have also carried out Raman scattering as a function of temperature from 18 K to 450 K. Temperature evolution of the peak positions of most of the modes can be adequately described using an anharmonic model suggesting absence of any lattice anomaly across the phase transitions. This observation is consistent with the XRD data. However, the temperature dependence of the line width of a number of modes exhibits a change in slope across the phase transition boundary. In order to understand and quantify this change in the line width as a function of temperature we calculate the product of electron-phonon coupling strength and the density of states at the Fermi level. The deviation from anharmonicity is qualitatively explained as a consequence of a weak magneto-elastic effect in the low temperature phase. [Preview Abstract] |
|
K1.00290: Power-law Griffiths singularities in a randomly layered Heisenberg magnet Fawaz Hrahsheh, Thomas Vojta We study the ferromagnetic phase transition in a randomly layered Heisenberg model using Monte-Carlo simulations. A recent strong-disorder renormalization group approach [Phys. Rev. B 81, 144407 (2010)] predicted that the critical point in this system is of exotic infinite-randomness type and is accompanied by strong power-law Griffiths singularities. Here, we show the results of simulations that provide numerical evidence in support of these predictions. Specifically, we investigate the finite-size scaling behavior of the magnetic susceptibility which is characterized by a non-universal power-law divergence in the Griffiths phase. In addition, we calculate the spin-wave stiffnesses both parallel and perpendicular to the layers. We find that the perpendicular stiffness decays to zero at lower temperatures than the parallel stiffness which vanishes at the critical point. [Preview Abstract] |
|
K1.00291: Density matrix Loschmidt echo and quantum discord in quantum phase transitions Yanchao Li We introduce the concept of the Loschmidt echo (LE) to the space of the reduced density matrix of spin and fermionic systems to study the relationship between the density matrix Loschmidt echos (DMLEs) and quantum phase transitions (QPTs). Our results show that the DMLEs are remarkably influenced by the criticality of the system, and the method is a convenient way to study QPT. Meanwhile, we compare quantum discord and DMLE calculations, aiming to explore the difference and connection between them in identifying QPTs. [Preview Abstract] |
|
K1.00292: Time Reversal Symmetry Breaking in 2D Lattice Model Wei Liu, Alexander Punnoose We use magnetic group as a tool to classify the possible spontaneous time-reversal symmetry breaking states in 2D electronic systems. We study the leading order fluctuations of the order parameter with discrete symmetry. The method is applied to the study of Topological Mott insulator phase in Graphene and orbital loop currents in CuO planes. [Preview Abstract] |
|
K1.00293: The Verwey transition in Fe$_3$O$_4$: lattice distortions on a fs time-scale R. Kukreja, S. de Jong, M. Hossain, C. Back, A. Scherz, D. Zhu, W. Schlotter, J. Turner, W. Lee, Y. Chuang, R. Moore, O. Krupin, M. Trigo, H. D\"urr, L. Patthey, N. Pontius, T. Kachel, A. F\"ohlisch, M. Beye, F. Sorgenfrei, W. Wurth, C. Chang, M. D\"ohler, C. Trabant, C. Sch\"ussler-Langeheine Magnetite, Fe$_3$O$_4$, displays a strong decrease in resistivity upon heating above $T_C= 123$~K: the Verwey transition. This transition is accompanied by a structural change from monoclinic to cubic symmetry. Despite decades of research and indications that charge and orbital ordering play an important role, the mechanism behind the Verwey transition is yet unclear. Using pump-probe soft X-ray scattering at the new LCLS SXR beamline, we have studied the role of the structural transition for the Verwey transition on ultra-fast time-scales. Focusing off-resonance on the high T forbidden (001) lattice reflection, we find a lattice response on time-scales $t< 250$~fs. The response displays a pump fluence threshold indicative of a phase transition. This strongly suggests that the lattice, via coupling to certain low energy phonon modes, plays a crucial role for the Verwey transition in Fe$_3$O$_4$. [Preview Abstract] |
|
K1.00294: Metal-insulator transition characteristics of epitaxial and polycrystalline SmNiO$_{3}$ thin films Sieu Ha, Gulgun Aydogdu, Shriram Ramanathan SmNiO$_{3}$ (SNO) is known to exhibit a sharp insulator to metal transition at 130 $^{\circ}$C in bulk form and is a candidate material for utilization in advanced electronic devices such as memory and neuromorphic circuits. We present growth and characterization of SNO thin films deposited on LaAlO$_{3}$ and Si single crystals. Structural properties such as crystallinity, strain, and stoichiometry are examined with x-ray diffraction and x-ray photoelectron spectroscopy. Temperature-dependent resistance measurements are performed, and a metal-insulator transition is observed for films on both substrates. We investigate how resistance changes are affected by thermal cycling and the role of surface oxygen loss on electrical characteristics. [Preview Abstract] |
|
K1.00295: Quantum phase diagram of the half filled Hubbard model with bond-charge interaction Ariel Dobry, Armando Aligia Using field theoretical bosonization, we determine the quantum phase diagram of the one-dimensional Hubbard model with bond-charge interaction $X$ in addition to the usual Coulomb repulsion $U$ at half-filling, for small values of the interactions. We show that it is essential to take into account formally irrelevant terms of order $X$. They generate relevant terms proportional to $X^2$ in the flow of the renormalization group (RG). The model shows three phases separated by a charge transition at $U=U_c$ and a spin transition at $U=U_s>U_c$. For $U < U_c$ singlet superconducting correlations dominate, while for $U > U_s$, the system is in the spin-density wave phase as in the usual Hubbard model. For intermediate values $U_c < U< U_s$, the system is in a spontaneously dimerized bond-ordered wave phase, which is absent in the ordinary Hubbard model with $X=0$. We provide an analytical expression for $U_s(X)$. The results, with only one adjustable parameter, are in excellent agreement with numerical ones for $X < t/2$ where $t$ is the hopping. [Preview Abstract] |
|
K1.00296: Neutron diffraction study of quasi-one-dimensional lithium purple bronze: possible mechanism for dimensional crossover John J. Neumeier, M.S. da Luz, C.A.M. dos Santos, B.D. White, H.J.I. Filho, J.B. Le\~{a}o, Q. Huang The crystallographic structure of quasi-1D lithium purple bronze was investigated using neutron powder diffraction at temperatures \textit{T} in the range 5 K $< T < $ 295 K. Lattice parameters, atomic positions, and occupation numbers are reported. At room temperature, it has a monoclinic symmetry with space group \emph{P}2$_1$/\emph{m}, lattice parameters \textit{a} = 12.750(1) \AA, \textit{b} = 5.524(1) \AA, \textit{c} = 9.491(2) \AA, and $\beta$ = 90.593(1)$^{\circ}$. The stoichiometry was determined through chemical analysis \textit{and} refinement of the NPD data to be Li$_{0.924}$Mo$_6$O$_{17.6}$. The bond-valence-sum method was applied to calculate the valence of each Mo ion as a function of \textit{T}, which allows discussion of the mechanism by which charge is transferred between the double 1D conducting chains. [Preview Abstract] |
|
K1.00297: Study of phase transitions in ternary lead indium niobate-lead magnesium niobate-lead titanate relaxor ferroelectric morphotropic single crystals Peter Finkel, Harold Robinson, Ahmed Amin In this work we report on the elastic hysteretic behavior observed in ferroelectric lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT) relaxor single crystals under conditions of cooperative stress, temperature, and electric field. Room temperature elastic response displays strong and sharp discontinuity associated with stress induced phase transition. Quasistatic elastic response and ultrasonic wave propagation measurements demonstrated that this strain discontinuity in PIN-PMN-PT single crystal is associated with a ferroelectric rhombohedral (FR)---ferroelectric orthorhombic (FO) phase transition. The temperature dependent elastic response and transition strain were modeled by Devonshire theory. The crystal instability under compression is significantly improved by application of a dc bias electric field. [Preview Abstract] |
|
K1.00298: $^1$H NMR Study of Proton Dynamics in the Ferroelastic Transition of K$_4$LiH$_3$(SO$_4$)$_4$ Cystals Moohee Lee, Ho Hyoun Kim, B.J. Mean, Ki Hyeok Kang, B. Ndiaye, Ae Ran Lim K$_4$LiH$_3$(SO$_4$)$_4$ is known to show a ferroelastic transition at $T_c$ = 114 K. We have performed $^1$H nuclear magnetic resonance(NMR) measurements to investigate proton dynamics in the phase transition of K$_4$LiH$_3$(SO$_4$)$_4$ crystals in the temperature range of 70-300 K at 2.67 T. The $^1 $H NMR spectrum shows a composite structure with dominating broad and weak narrow components. The broad component has an extremely long $T_1$ whereas the narrow component exhibits a short $T_1$ at room temperature. The intensity of the narrow peak decreases at low temperature vanishing below 200 K. From this behavior, we find that the narrow component comes from rapidly moving protons whereas the broad component originates from rigid protons. From the temperature dependence of the short $T_1$ for the narrow component, the activation energy for the proton's rapid motion is deduced to be $\sim$1900 K. On the other hand, the long $T_1$ for the broad component decreases at low temperature suggesting that the proton dynamics associated with the ferroelastic transition change abruptly across $T_c$. [Preview Abstract] |
|
K1.00299: Ion conductivity relaxation and specific heat close to the first-order phase transition of $\gamma -$RbAg$_{4}$I$_{5}$ Ruben A. Vargas, Hernando Correa, Diego Pe\~na-Lara We report on simultaneous measurements of specific heat at normal pressure and ac conductivity in single-crystalline $\gamma $-RbAg$_{4}$I$_{5}$ close to and below its $\gamma $-to-$\beta $ first order phase transition at 121 K. We found an accurate proportionality between the specific heat, \textbf{\textit{c}}$_{P}$, and the temperature derivative of the product \textbf{\textit{nE}}$_{\sigma }$, where \textbf{\textit{$\beta $ =1- n}}, is the Kohlrausch stretching exponent for the conductivity relaxation and \textbf{\textit{E}}$_{\sigma }$\textbf{\textit{ = d(ln$\sigma )$/d(T}}$^{-1}$\textbf{\textit{)}} is the dc conductivity activation energy, which is non-Arrhenius. Thus, our results show that the dc conductivity activation energy \textbf{\textit{E}}$_{\sigma }$\textbf{\textit{(T)}} includes, besides the true microscopic energy ``barrier'' for independent ionic motion, \textbf{\textit{(1-n) E}}$_{\sigma }$ (according the coupling model), an additional contribution from the enthalpy of the mobile Ag-ions defects, \textbf{\textit{h}}. [Preview Abstract] |
|
K1.00300: Critical dynamics of randomly layered magnets Hatem Barghathi, Thomas Vojta We report the results of large-scale Monte-Carlo simulations of the critical dynamics in the randomly layered Heisenberg model. This system has recently been reported to display an exotic phase transition controlled by an infinite-randomness critical point [Phys. Rev. B 81, 144407 (2010)]. In agreement with this, we found the critical dynamics to be ultraslow. At criticality, the time autocorrelation function decays only logarithmically with time while it follows a nonuniversal power-law in the Griffiths phase. We also study the case of XY spin symmetry where the interplay between the randomness and the Kosterlitz-Thouless physics leads to even stronger disorder effects. [Preview Abstract] |
|
K1.00301: A second metastable spin-ordered state on ferrimagnetic single crystal Cu$_{2}$OSeO$_{3}$ Chih Chieh Chou, C.L. Huang, K.F. Tseng, S. Mukherjee, J.L. Her, Y.H. Matsuda, K. Kindo, H. Berger, H.D. Yang DC and AC susceptibilities were executed on ferrimagnetic single crystal Cu$_{2}$OSeO$_{3}$ under magnetic field ($H)$ and hydrostatic pressure ($P)$ circumstance. With increasing $H$, the ferrimagnetic transition at $T_{C} \quad \sim $ 60 K tends to a higher temperature. Furthermore, the $T_{C}$ rises with a linear slope and magnetization is enhanced with increasing $P$. Features of the ladder shown in the $M$ vs. $H$ curve or the peak observed in the d$M$/d$H$ vs. $H$ curve are noted at $H_{SF} \quad \sim $ 0.5 kOe, exhibiting a competing ordered state in magnetic fields below $T_{C}$. Remarkably, another shoulder is observed at $\sim $ 1 kOe in the d$M$/d$H$ vs. $H$ curve, revealing a metastable spin ordered state in Cu$_{2}$OSeO$_{3}$. In addition, the novel state is retained and enhanced by applied pressure. However, at $H$ up to 55 T, there is no more observable slop change in magnetization. These magnetic properties suggest a complex spin orientation in the spin-frustrated system Cu$_{2}$OSeO$_{3}$. [Preview Abstract] |
|
K1.00302: Current Bearing Electron Shock Wave Mostafa Hemmati For analytical solution of breakdown waves, we use a one-dimensional, steady-state, three-component (electrons, ions, and neutral particles) fluid model. The wave front is considered to be a shock front and the electron gas partial pressure is considered to provide the driving force for the propagation of the wave. The basic set of equations consists of the equation of conservation of mass flux, equation of conservation of momentum, equation of conservation of energy, plus Poison's equation. In this study, the emphasis will be on the waves propagating into a neutral medium and we will investigate breakdown waves for which a large current exist behind the wave front. We apply shock conditions to obtain breakdown wave profile for electric field, electron velocity, electron temperature, electron number density, and ionization rate behind the shock front for breakdown waves propagating in the opposite direction of the electric filed force on electrons. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700