Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session T70: Poster Session III(1:00pm-4:00pm)Poster
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Room: BCEC Exhibit Hall |
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T70.00001: GENERAL
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T70.00002: A Neoclassical Framework That Reunifies Modern Physics Alan M. Kadin The unity of classical physics was broken by quantum uncertainty on the micro level and curved spacetime on the cosmic level. In contrast, a novel neoclassical picture is presented*, which incorporates key aspects of quantum and relativistic physics, while maintaining deterministic local reality at all levels. This is based on the following principles: |
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T70.00003: Mesoscopic RLC Circuit and its Associated Occupation Number and Berry Phase Eric Greenwood We consider the quantization of the time-dependent harmonic oscillator and its associated |
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T70.00004: Tracking UV photolysis and molecular transport induced chemical changes within tissue models treated with a cold atmospheric pressure plasma jet Bhagirath Ghimire, Pradeep Lamichhane, Eun Ha Choi Cold atmospheric plasma jets operated into ambient air provide a rich source of reactive oxygen and nitrogen species (RONS), which are known to influence biological processes important in disease. Despite plasma shown to have effects deep within tissue (e.g. destruction of subcutaneous cancer tumors), it is not understood how the plasma RONS can reach deep-seated diseased cells. In this study, we model the plasma jet delivery of RONS into a tissue target and we delineate two processes: through target delivery of RONS generated (primarily) in the plasma jet and in situ RONS generation by UV photolysis within the target. RONS are rapidly generated in the tissue target’s surface by UV photolysis. Once in the target, RONS are transported to millimeter depths via a slower molecular process |
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T70.00005: Convolutional Autoencoder for Denoising Images of Active Nematics Zhengyang Zhou, Pengyu Hong, Michael Norton, Seth Fraden The images produced in active nematics experiments are usually quite noisy. These noises (caused by the activities of materials, lighting, etc.) can significantly influence the downstream analyses and constraint our capability of understanding active nematics. Conventional denoising methods have limited power in improving the quality of those images. In this study, we developed a Deep Learning technique to tackle this problem. We designed a deep denoising model as a deep convolutional auto-encoder with skip-layers. The deep denoising model was trained using randomly chosen clean images of active nematics. We also designed a convolutional reconstruction method that uses our deep denoising model to remove noises in new active nematics images. Experimental results demonstrate the effectiveness of our approach. |
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T70.00006: Spectral Stability of Gravitationally Interacting Rods Carlos Owusu-Ansah, John Lindner We investigate the spectral stability of equilibrium configurations of two line-masses (slashes or rods) interacting via gravity. The Euler-Lagrange formalism provides the equations of motion. We determine the positions, orientations and angular velocities of the slashes at their equilibrium configurations. All equilibrium solutions are checked using the equations of motion. The spectral stability of each equilibrium configuration is determined by linearizing the equations of motion about the equilibrium configurations and analyzing the path of the slashes when they are perturbed. We illustrate the parameter values that cause equilibrium configurations to be spectrally stable. |
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T70.00007: Sliding on a Spinning Cuboid Kimberly Patterson, John Lindner Which way is downhill on a spinning asteroid? Comet nuclei and asteroids like 67P, Ryuga, and Bennu are too small to gravitationally pull themselves into spheres. As spacecraft like Rosetta, Hayabusa2, and OSIRIS-REx visit them, a better understanding of the surface motion of regolith and boulders, as well as hoppers, landers, and rovers, is needed. For a theoretical overview, previous work studied the frictionless sliding of point masses on spinning asteroids idealized as rotating spheroids. In this work, we concentrate the curvature into 12 edges and study the periodic and chaotic motion of point masses sliding frictionlessly on rotating cuboids. |
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T70.00008: Three Roads to Quaternion Gravity Douglas Sweetser Three roads merge to create a different approach to gravity. Our deepest insights into nature use symmetries because symmetries remain unchanged. Using quaternion algebra instead of tensor calculus, the conservation of space-times-time is the symmetry underlying the quaternion gravity proposal for non-inertial observers in a gravitational field. Where there is a symmetry, there need also be a transformation law to detail how change is permitted to happen. The notion of relaxed relativity holds that in a gravitational field, one observer looking at another observer measuring the speed of light will find the product of wavelength and frequency differs from the speed of light c in a precise way (c'=cγ2esc). Lorentz invariance remains for inertial observers, but non-inertial observers are governed by different symmetries. Gravity is different everywhere, so a field theory is also necessary using gravitational escape velocities. With some reasonable guesses constrained by observations, one can form a quaternion gravity proposal that is consistent with weak field gravity tests to first order Parameterize Post Newtonian accuracy. No gravitons are required for this technical variant of special relativity. Pre-print available on line: http://bit.ly/vp-three-roads |
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T70.00009: Detection of biomarkers in lipidic cubic phases Munir Pirbhai Lipidic cubic phases have been shown to be versatile platforms for the detection of biomarkers, viruses, bacteria and parasites. This technique produces birefringent crystals during a positive test, which can be detected by placing the sample between crossed-polarizers and shining light through. The intensity of light emerging from the setup constitutes the output signal, and can be related to the concentration of analyte present. In this work, we investigate how the thickness of the sample affects the output signal. |
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T70.00010: Gravity and Waves and Dimension Reduction Thomas Materdey, Albert Materdey, Alexander Materdey Gravity can interact with a mechanical wave to convert a 3D object into a 1D string, thus reducing space-time dimensions from 4 to 2. The physics of this gravity-wave interaction could form the basis of a semi-classical approach to quantum gravity. |
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T70.00011: MEDICAL PHYSICS
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T70.00012: Hyperspectral imaging of human hands and curvature correction Luka Rogelj, Urban Pavlovčič, Jošt Stergar, Rok Dolenec, Matija Jezeršek, Matija Milanic, Urban Simončič Hyperspectral imaging (HIS) is a non-contact and non-invasive method that provides spectral and spatial information in a single measurement. It has been recently introduced into the medical imaging as a research tool for determination of physiological parameters distribution (e.g., hemoglobin and oxygenation maps). |
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T70.00013: Curvature statistics: An underused measure for epithelial to mesenchymal transition classification in pancreatic cancer Jeffrey La, Jonathan P Celli, Chandra S Yelleswarapu Epithelial to mesenchymal transition (EMT) and mesenchymal to epithelial transition (MET) plays an essential role in the local progression and metastasis of pancreatic cancer, whereby malignant cells undergo a physical transformation associated with increased mobility and resettle in a new site. Discovering EMT and MET’s underlying molecular processes have opened new therapeutic agents, however knowledge of this complex network is not complete and design consistencies in literature limit inferences and prevent meta-analysis of data. Instead of focusing on chemical pathways, we revisit ways to characterize cellular shape through cellular curvature distribution. We demonstrate this measure can improve classification models of epithelial, mesenchymal, and transitioning cells, with pancreatic cancer cells by computational analysis of optical microscopy images, which can improve risk stratification and treatment decisions. |
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T70.00014: Sub-Nano Pulsed Laser Transport through Different Skin Types for Tattoo Removal Application Shah Faisal Mazhar, Reginald Eze
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T70.00015: Material Design for Near-Infrared Photothermal Therapy Faith Cheung, Xuan Luo Photothermal therapy, as a promising and emerging method of cancer treatement, uses the emission of near-infrared light for tumor ablation. However, current photothermal agents have led to inefficient tumor ablation due to its inability to penetrate deeply into affected tissue. In our research, we perform first-principles calculations to find the optimal materials for near-infrared light emission by doping graphene. Our results show the band gaps corresponding to near-infrared light emission and we claim that oxygen doped graphene is a suitable source for near-infrared light. It is possible to improve the efficiency of photothermal therapy by using these materials, hence our results pave the way for photothermal therapy. |
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T70.00016: APPLICATIONS
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T70.00017: Controlling the EMI Shielding Properties of Conductive Fused Deposition Modeling Material Logan Truman, Lucas J Koerner, Brittany Nelson-Cheeseman Recently, 3D printing has become more popular due to the availability of new materials. For example, electrically conductive graphene-PLA composites can be used as a shield for electromagnetic interference (EMI); specifically, circuit packages 3D printed using conductive composites could provide shielding. The purpose of this research is to determine how the parameters of 3D printed samples impact the shielding effectiveness. Our previous research has shown that the percentage and orientation of infill has the greatest impact on conductivity. Here, we test shielding effectiveness from 10 MHz to 3 GHz by measuring RF transmission through a sample by sandwiching it between a custom coaxial tester connected to a spectrum analyzer. The data showed that the greater the infill percentage, the less the orientation effects attenuation. For example, 100% infill samples with perpendicular and parallel orientation both attenuated by -15 dB at 1 GHz. However, at lower infill percentages, more varied infill orientations differed in RF attenuation. For example, at 25% infill, samples with perpendicular and parallel infill attenuated by -20 dB and -12 dB at 1 GHz, respectively. The most efficient sample by mass had 25% infill orientated at 4 varying angles. |
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T70.00018: "Coherent Illumination-Direction-Multiplexing Dual-Space and Fourier Ptychographic Microscopy" Hira Farooq, Sueli Skinner Ramos, Luis Grave de Peralta We present a variation of the Fourier ptychographic microscopy (FPM) algorithm adapted for imaging samples simultaneously illuminated by multiple beams coherent with each other. The modified algorithm was successfully tested using the light diffracted by a Ronchi-ruling as the source of illumination. We describe proof-of concept experiments demonstrating, first, that the presented method permits to recover the structure of the sample from a set of low-resolution RP images containing not the images of the sample, but Moiré patterns carrying information about the structure of the sample. Second, we demonstrate the capability of the presented method for obtaining images of the sample with a resolution better than the Rayleigh resolution limit. |
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T70.00019: ABSTRACT WITHDRAWN
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T70.00020: ABSTRACT WITHDRAWN
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T70.00021: Phase-Change Materials for Photonic Limiters Tony Liu, Meng-Ju Sher Limiters, with their optical properties highly dependent on the wavelength and intensity of the incoming light, are often used to protect sensitive optical components. Currently most limiters are sacrificial, destroyed after a single high intensity exposure. As an alternative, this work focuses on photonic limiters because they significantly increase the cost-efficiency by their high damage threshold and reusability. We study a photonic limiter design with phase-change material (PCM) as a key component. To incorporate PCM in the limiter design, we use ellipsometry to characterize PCM optical property at a wide range of wavelength and temperature. An example of such materials is GeSbTe (GST), an alloy consisting of germanium, antimony and tellurium. Around a critical temperature, GST transforms from amorphous to crystalline, thereby switching its optical properties. Besides GST, we also examine the optical properties of other semiconductors such as ZnO and GaAs as possible material for other limiter designs. |
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T70.00022: Lithium niobate optomechanical crystal Wentao Jiang, Rishi N Patel, Felix Mayor, Timothy McKenna, Patricio Arrangoiz-Arriola, Christopher Sarabalis, Raphaël Van Laer, Amir Safavi-Naeini Lithium niobate (LN) has excellent piezoelectric and electro-optic properties, enabling it as the workhorse material of the essential components for classical communication. Recently LN is also considered for quantum signal transduction and modulation. High-quality LN microring resonator and LN photonic crystal have been demonstrated with quality factor as high as 107 and 105 respectively. |
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T70.00023: Influence of ZnTe nanocrystals in the laser performance parameters of Yb3+ doped phosphate glasses Alysson Miranda Freitas, Rodrigo Ferreira Falci, Maria Jose V Bell, Noelio Oliveira Dantas, Virgilio Anjos This work reports an optical investigation of a phosphate glass (PZABP) doped with ZnTe semiconductors nanocrystals and co-doped with Yb2O3. ZnTe nanocrystals growing were evidenced by optical absorption spectra and their average radius were estimated via effective mass approach. The emission cross section, absorption cross section and lifetime measurements were performed via Optical Absorption, Photoluminescence and Time-Resolved Photoluminescence techniques. Important performance parameters for solid-state lasers, like the minimum fraction of ions that must be excited (βmin), the pump saturation intensity (Isat) and the minimum intensity of the pumping laser (Imin) were obtained and the product σemi × texp was defined as a figure of merit to analyses the efficiency of the system. The influence of the ZnTe nanocrystals in the laser performance parameters was studied. The results point the alterations caused by the presence of the nanostructures may be compensated by the intensity gain on the media active and indicates the PZABP glasses as a promising material to applications in high power lasers. |
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T70.00024: Role of Ni2+ in transparent glass-ceramics with semiconductor nanocrystals for optoelectronic applications Radha Mada, Seshadri Meruva, Maria Jose V Bell, Noelio Oliveira Dantas, Virgilio Anjos Phosphate glass doped with 5 wt% Ni2+ ions and glass-ceramics containing ZnTe nanocrystals with x wt% of Ni2+ ions (x = 0.5, 1.0, 5.0 and 10.0) were prepared by fusion method. The structural analyses were performed through XRD, FTIR-ATR and Raman techniques. The XRD revealed amorphous and ZnTe crystalline phases. Several phosphate groups were observed from FTIR-ATR and Raman spectra showing that Ni2+ ions possess octahedral symmetry. The intensity of the1352 nm band increased with the increase of Ni2+ ions in GC which is an indicative of the 6Ni2+ coordination. The emission cross-sections (semi), full width at half maxima for the 1T2g(D)→3T2g(F) and 3T2(F)→3A2(F) emissions were reported. The product of semi and tm (figure of merit) and semi (3T2(F)→3A2(F) ) was higher to GC sample with 10.0 wt% of Ni2+. Thermal diffusivity (D) and thermal conductivity (K) were obtained through thermal lens and thermal relaxation methods. D and K did not change significantly with the increase of Ni2+ ions (0.5 – 5 %) in GCs. The 10.0 wt% Ni2+ sample presented the lower variation of the optical path with temperature with good lasing properties suggesting it as good candidate for optoelectronic applications. |
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T70.00025: Computational electro-magnetic field modeling of TMS coils with validation in gel-based phantom brain John R Germick, Xiaojing Zhong, Yifei Wang, Aaron Boes, Hiroyuki Oya, David C Jiles Transcranial magnetic stimulation (TMS) is a noninvasive brain stimulation technique for modulation of cortical neurons in the brain. One challenge with the use of TMS is that it is often difficult to determine the spatial distribution of brain regions receiving stimulation. A popular method of exploring the stimulation profile of TMS coils is through generation of virtual head models and Finite Element Simulations (FEM). However, a limitation of this approach is the models are rarely validated against actual measurements of the magnetic and electric fields. Here, we performed FEM modeling on gel-based phantom brain models with conductive properties that mimic those of the human brain. The phantom brains had implanted electrocorticography electrodes at varying depths to record the stimulation profiles recorded by the electrodes, which were then compared with FEM models of the phantom brain. Ongoing work is focused on validating FEM results relative to a novel paradigm of recording the effects of TMS in neurosurgical patients with intracranial EEG. Taken together, this work highlights the strengths and limitations of using FEM to simulate the magnetic and electric field profiles generated by TMS coils, and propose a new method of testing the performance of novel TMS coils. |
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T70.00026: Investigating how coil designs and anatomical variations affect the efficacy of cerebellar TMS Xiaojing Zhong, Priyam Rastogi, Yifei Wang, Erik G Lee, David C Jiles Transcranial magnetic stimulation (TMS) is a neuromodulation technique a non-invasive treatment for various neurological disorders such as major depressive disorder. Cerebellum is a complex structure connected with almost the entire central nervous system, and TMS has promise for non-invasively probing cerebellar function. Therefore, TMS has been gaining popularity in the field of neurostimulation of cerebellum. Recent studies have reported that cerebellum plays an important role not only in motor planning and behavior but also in the cognitive domain. Nevertheless, few studies have explored how different coil designs and anatomical variations affect the effectiveness of cerebellar TMS. In this work, we investigated the effects of cerebellar TMS with different coil designs positioning on several locations. Finite element modeling was conducted with Figure-of-8 coil and DB-80 coil. Each coil was positioned in the center, 1 cm and 3 cm to the left with respect to the center of the cerebellum and all the locations were tangential to the scalp at a distance of 5 mm. Furthermore, the commercial head model MIDA and 50 MRI derived head models were used in the computer modelling to examine how anatomical variations affect the efficacy of cerebellar TMS. |
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T70.00027: Magnetic properties of synthesized Fex(Fe3O4)1-x nanoparticles with core-shell structures coated by carbon matrix Aram Manukyan, Harutyun Gyulasaryan, Eduard Sharoyan, Jennifer Lynn Gray, Oscar Bernal, Armen Kocharian Here we are focused on investigation of magnetic and structural properties of synthesized nanocomposites with iron nanoparticles as effective heat mediators with high thermal energy transfer efficiency suitable for use for magnetic hyperthermia. These nanoparticles have “core-shell” structure, in which the core has a high magnetic moment (such as Fe), and the shell consists of a biocompatible material (e.g. iron oxide or carbide). Complex investigations of structural and magnetic properties of these materials are obtained using X-ray diffraction (XRD), Raman spectroscopy, magnetometry, electron paramagnetic and ferromagnetic resonances (EPR, FMR). The measured magnetization of magnetic saturation and coercivity as well as the specific absorption rate (SAR) show that these materials attractive for magnetic hyperthermia applications. Hysteresis loop of the (Fe-Fe3C)@C nanocomposites is of special interest as it shows almost square behaviour, where Mr/M(200 Oe) = 0.75. |
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T70.00028: Nucleic Acid Functionalization of Graphene and the Impact on Stem Cell Maturation Vincent Battisini Olivieri, Lan Wei, Michelle Chen, Howard H Chen Stem cells are capable of differentiating into defined cell types, thus hold great promise for medical applications including disease modeling, drug screening, and therapeutics. When integrated with graphene, an extremely conductive and strong atomic sheet of carbon atoms, novel ways to understand and control the differentiation of stem cells may be realized. We hypothesize that nucleic-acid functionalized graphene minimally impact stem cell viability, and can further enhance stem cell differentiation. In our experiments, various nucleic acid constructs were successfully purified and characterized before functionalization onto graphene, which was synthesized on copper via chemical vapor deposition and then transferred onto glass coverslip. Stem cells, primary bone marrow mononuclear cells (BMMCs), were isolated from mice and cultured on nucleic acid functionalized graphene. Preliminary atomic fore microscopy revealed prominent 3-dimensional features of greater than 30 nm in height 24 hours after stem cell attachment, suggesting the presence of viable BMMCs. Furthermore, cell topography and significant adhesion to nucleic acid-graphene substrate suggests robust cell viability. Our findings indicate potential enhancement of graphene for stem cell viability and differentiation. |
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T70.00029: INSTRUMENTATION AND MEASUREMENTS
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T70.00030: Determination of cantilever's spring constant by using single-optic-fiber radiation-pressure technique Heonhwa Choi, Jae-Hyuk Choi We generated sub-femtonewton radiation-pressure forces to drive a very soft silicon-nitride cantilever without highly reflective coating and determine its spring constant in the range of 10-5 N/m. To be applicable to cantilevers of general dimensions and reflectivity, we built an experimental setup with a single optic fiber accessing a cantilever surface and an in-situ reflectivity measurement feature. A 1320-nm laser from a superluminescent diode was used to generate oscillating forces of 0.2–1 femtonewton, and a tunable laser to measure the cantilever’s displacement and its absolute distance from the fiber. The origin of the discrepancy between the obtained and bulk values of silicon-nitride reflectivity is to be discussed. |
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T70.00031: Development of the Millimeter-wave Camera with High Time Resolution for Observation of the Vortex Beam Asaki Tanabe, Tokihiko Tokuzawa, Yuki Goto, Toru Ii Tsujimura, Shin Kubo Recently, it has been shown that a charged particle with spiral motion creates a radiation field with vortex property [1]. Since an electron in the magnetic field confinement fusion plasma has a spiral motion (electron cyclotron motion), the electron cyclotron emission (ECE) should have a vortex property. In order to demonstrate the vortex property, we will investigate the ECE from the gyro phase control electron. In this research, radiation pattern measurement of less than millisecond is required, so we are developing millimeter wave camera with high temporal resolution. |
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T70.00032: Extracting Ion Transport Properties from Scanning Probe Measurements on Smectite Clay Nanoparticles Aydin Wells, Kelsey Yee, N. E. Israeloff Using finite element modelling, electronic simulations under an electrical load can be designed to better understand ion transport properties of smectite clay nanoparticles (NP). Smectite clay is a layered, porous material capable of changing its physical properties when hydrated upon exposure to water vapor. With a conducting atomic force microscope (AFM) tip, scans on the surface of these particles were done; data relating to particle topography and frequency-dependent electric forces was extracted from these experiments. A finite element method (FEM) model and Matlab programs were constructed to facilitate simulation of AFM system parameters, measurements, and computation. The equivalent charge method offered an advanced approach to computing NP electric properties with the irregular shaped AFM tip by modeling the force resulting from a series of test charge-image interactions. FEM simulations revealed that dielectric phase shift followed a power law with increasing voltage frequency on the AFM tip. With different conductivity anisotropy, force derivative and phase shift values were observed to have different frequency dependencies. Computational results were paired with experimental findings to extract frequency dependant NP conductivity to compare to bulk measurements. |
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T70.00033: Measuring the Casimir Force with a Commercial MEMS Accelerometer Alex Stange, David John Bishop The Casimir Effect is a physical manifestation of quantum fluctuations of the electromagnetic vacuum. When two metal plates are placed closely together, typically much less than a micron, the long wavelength modes between them are frozen out, giving rise to a net attractive force between the plates, scaling as d^-4 (or d^-3 for a spherical-planar geometry) even when they are not electrically charged. In this work we show that by modifying a post-release MEMS accelerometer, similar to the one in your phone, we can actually measure this effect in ambient conditions. This device is a step towards leveraging the Casimir Effect for cheap, sensitive, room temperature quantum metrology. |
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T70.00034: Superconducting Nanowire Single Photon Detectors for Nuclear Physics Tomas Polakovic, JOHN E. PEARSON, Axel F Hoffmann, Volodymyr Yefremenko, Clarence Chang, Whitney Armstrong, Zein-Eddine Meziani, Kawtar Hafidi, Goran Karapetrov, Valentyn Novosad Superconducting nanowire single photon detectors (SNSPD) are becoming the most prominent technology in the fields of nanophotonics and quantum information sciences because of their excellent detection efficiency and timing capabilities. The possibility of high detection rates and superior timing jitter, they are also an attractive technology in the field of nuclear and particle physics as a replacement for conventional light detectors or as detectors of charged particles. These applications have unique challenges, as the detectors need to operate in strong magnetic fields and withstand radiation damage. |
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T70.00035: HAXPES Lab: A novel laboratory-based Hard X-ray Photoelectron Spectroscopy System Anna Regoutz, Manfred Mascheck, Tomas Wiell, Susanna Eriksson, Cristopher Liljenberg, Kornelius Tetzner, Benjamin Williamson, David Scanlon, Paul Palmgren Hard X-ray photoelectron spectroscopy (HAXPES) uses X-rays in the 2-10 keV range to excite photoelectrons, which are used to non-destructively probe the local chemistry and electronic structure of materials. It is particularly useful as it can be applied to bulk as well as structured samples. HAXPES is a powerful technique for the study of buried layers and interfaces in multilayer thin film stacks and composite materials. Up to now HAXPES was only available at synchrotron sources, which provide the necessary intense, high energy X-rays. |
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T70.00036: Diffraction of the Millimeter Wave with Vortex Property by a Triangular Aperture Yuki Goto, Toru Ii Tsujimura, Shin Kubo Recently, it has been shown that a radiation from a charged particle with spiral motion has vortex property. Various researches regarding a vortex beam has been carried out not only in the visible region but also in the various frequencies. Since an electron cyclotron motion is also spiral motion, an Electron Cyclotron Emission (ECE) should have vortex property. In order to experimentally demonstrate the vortex property of ECE, we have tried to generate the gyro-phase controlled multi-electron system, which can actively emit the ECE with vortex property. For this experiment, we developed the method to estimate the vortex property and to identify the Topological Charge (TC). This method is successfully checked by using the passively generated vortex beam from Gaussian beam in the millimeter wave region. The diffraction pattern by a triangular aperture of the passively generated vortex beam is observed. Since the diffraction pattern depends on the TC, we can identify the TC of the vortex beam. As a result, we were able to measure the characteristic diffraction patterns of millimeter wave vortex beam by a triangular aperture for the first time in the world. We will show the details of the experimental and calculation results. |
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T70.00037: Increasing Solution Viscosity in Dynamic Light Scattering to Lower the Detection Limit for the Determination of Nanoparticle Size Hristo Ivanov, Bryan Augstein, Anton Wiggins, Clayton Palmer, Jeffrey Simpson We report on the development of homebuilt Dynamic Light Scattering (DLS) instrumentation to measure the size of monodisperse (MD), spherical nanoparticles (NPs) of gold. HeNe and Ar-ion lasers constitute the excitation sources for the scattering experiment, while an avalanche photodiode detects the scattered light, and an autocorrelation card analyzes the resulting signal to provide a measurement of the translational diffusion coefficient, which allows for the determination of NP diameter. We characterized our instrumentation using commercially-produced gold NPs with diameters ranging from 50nm to 200nm in aqueous solution. Given the strong temperature-dependence of the solution viscosity, periodic ambient temperature measurements were used to produce dynamic values for viscosity and minimize uncertainty in the determination of NP size. Increasing the liquid viscosity slows down the Brownian motion of the NPs and affords measurement of smaller-sized particles that otherwise diffuse too fast for detection. Currently we are suspending NPs in higher viscosity solutions in an effort to lower our size detection floor from approximately 50nm to 10nm. |
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T70.00038: Complex Materials Scattering (CMS) Beamline at NSLS II: Recent Developments and Progress toward Autonomous Exploration of Material Structure Masafumi Fukuto, Ruipeng Li, Kevin G. Yager The CMS beamline at the National Synchrotron Light Source II provides small- and wide-angle x-ray scattering (SAXS/WAXS) capabilities for materials science community. Since 2017, CMS has been supporting user experiments involving a wide range of materials, from polymers, nanocomposites, liquid crystals, biomolecular materials, to self-assembled nanoparticle superlattices and lithographic nanostructures. To promote efficient exploration of material parameter spaces, CMS has implemented a variety of high-throughput and in-situ capabilities. Besides basic transmission and grazing-incidence (GI)SAXS/WAXS capabilities, CMS has demonstrated, and offers, technically demanding capabilities such as specular reflectivity, variable-angle methods (CD-SAXS/CD-GISAXS), and grazing-incidence scattering tomography. We will discuss these developments as well as our recent progress with implementing autonomous x-ray scattering experiments in which decision-making algorithms are integrated into a closed-loop beamline workflow pipeline. |
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T70.00039: Atomically Resolved Probe-type Scanning Tunneling Microscope for Use in Harsh Vibrational Cryogen-free Superconducting Magnet Wenjie Meng, Jihao Wang, Yubin Hou, Mengqiao Sui, Junting Wang, Gang Wu, Jing Zhang, Junyun Li, Qingyou Lu We present a probe-type scanning tunneling microscope (STM) with atomic resolution that is designed to be directly inserted and work in a harsh vibrational cryogen-free superconducting magnet system. When a commercial variable temperature insert (VTI) is installed in the magnet and the STM is in turn housed in the VTI, a lowest temperature of 1.6 K can be achieved, where the STM still operates well. We have tested it in an 8 T superconducting magnet cooled with the pulse-tube cryocooler (PTC) and obtained atomically revolved graphite and NiSe2images as well as the scanning tunneling spectrum (STS, i.e. dI/dV spectrum) data of the latter near its critical temperature, which show the formation process of the superconducting gap as a function of temperature. The drifting rates of the STM at 1.6 K in X-Y plane and Z direction are 1.15 and 1.71 pm/min respectively.This is important as a cryogen-free magnet system has long been considered too harsh for any atomic resolution measurement. |
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T70.00040: New Design for Inertial Piezoelectric Motors Jing Zhang, Lige Liu, Wenjie Meng, Jihao Wang, Yubin Hou, Qingyou Lu We have designed, implemented, and tested the performance details of a new type of piezoelectric motor called the CicadaDrive. It is a new motor design that the total friction force can be dramatically reduced or even canceled by pushing the clamping points at the ends of a piezoelectric tube in the opposite directions during piezoelectric deformation. While our new motor requires the addition of another piezoelectric tube, which leads to an increase in volume of 120% when compared with traditional inertial piezoelectric motors, we can realize far greater performance than two times, including step size, threshold voltage, stability, etc. Its highly integrated structure means that this motor is suitable for use as either a motor or a scanning unit. |
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T70.00041: Terahertz Interferometric Microscopy Yesenia A. García, Naser Qureshi, Dahi Ludim Hernandez-Roa, Jesus Garduño-Mejía, Carlos Gerardo Treviño-Palacios We report on the development of a continuous wave near-field scanning microscope operating in the 500-600GHz frequency range. The use of interferometric detection allows for enhanced sensitivity and the use of low cost thermal detectors even when using a low power radiation source. We present representative images of both soft and hard matter samples. |
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T70.00042: Computing the 3D Radial Distribution Function: An Advanced Analytic Approach Bernd Kopera, Markus Retsch The radial distribution function, g(r), is ubiquitously used to analyze the internal structure of particulate systems. Applications range from molecular dynamic simulations to confocal microscopy of colloids. Measured particle coordinates are always confined in a finite sample volume. Computing g(r) is challenging once the radial distance, r, extends beyond the sample boundaries in at least one dimension. State of the art algorithms for g(r) use artificial periodic boundary conditions to circumvent this challenge. Ignoring the finite nature of the sample volume distorts g(r) significantly. Here, we present a simple, analytic algorithm for the computation of g(r) in finite samples. No additional assumptions about the sample are required. The key idea is to use an analytic solution for the intersection volume between a spherical shell and the sample volume. In addition, we discovered a natural upper bound for the radial distance that only depends on sample size and shape. |
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T70.00043: In Operando micro-Raman 3D thermometry with diffraction-limit spatial resolution
for GaN-based light-emitting diodes T. Park, Yong Zhang, Yong-Jing Guan, Zhiqiang Liu Confocal micro-Raman microscopy performed in the transparent spectral region of a semiconductor can in principle be used for operando 3D thermometry with optical diffraction-limit spatial resolution. However, when applied to high power GaN-based light-emitting diodes (LEDs), the applicability is hindered by the often strong secondary electroluminescence (EL) in the visible spectral region that overwhelms the Raman signal. We develop a “split-time-window” scheme that can mimic the continuous wave (CW) operation but without the interference of the secondary emission, which allows us to carry out noninvasive 3D temperature profiling, thus, a comprehensive thermal analyses of the whole device, at any operation current. The technique is applied to an InGaN/GaN LED to extract its 3D temperature distribution when operated at 350 mA with µm scale resolution when using 532 nm laser. We show that although a conventional technique can yield reliable average temperature difference between the heat sink and the LED junction (a few degrees), the spatial fluctuations are much larger than the average difference. Furthermore, we show that using anti-Stokes to Stokes Raman intensity ratio as metric can yield more reliable and accurate results than using Raman frequency shift. |
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T70.00044: Chromatographic 3He purification system, with an acoustic purity monitor Wenguang Jiang, Yoonseok Lee, Brodie Popovic, Colin Barquist A system for Helium extraction and purification (SHeEP) is constructed around a chromatographic cylinder filled with activated charcoal to remove 4He contamination from 3He gas [1]. In order to monitor the composition of the mixture during the process, an acoustic cavity is designed. The acoustic cavity measures the average atomic mass of the mixture by measuring the speed of sound [2][3]. The sensitivity of the acoustic cavity is estimated to be 0.04%. It provides a cheap alternative to a mass spectrometer. |
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T70.00045: Axisymmetric Neutron Analyzers to Enable Efficient Powder Neutron Diffractometers Boris Khaykovich, Ibrahim Alnami, Alexandru Stoica, Jay Theodore Cremer State-of-the-art thermal neutron sources are large expensive national facilities, which serve a diverse community of scientific and industrial users. The need to improve the performance of neutron instruments stems from the fact that most neutron methods are limited by the available flux, even at high-flux facilities. Many neutron methods cannot be used effectively at small sources available at universities and industrial laboratories. Thus, the efficient use of neutron flux is important for the progress and broader use of these neutron techniques. We present a novel design of an axisymmetric analyzer for powder diffraction to enable polychromatic cold and thermal neutron diffractometers, which will have much higher throughput than existing instruments and enable diffractometers at small reactors or even laboratory neutron generators. At the large neutron sources, such analyzers would enable fast screening of multiple samples or measuring kinetic processes. |
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T70.00046: Mask aligner for ultrahigh vacuum with capacitive distance control Priyamvada Bhaskar, Simon Mathioudakis, Tim Olschewski, Florian Muckel, Jan Rafael Bindel, Marco Pratzer, Marcus Liebmann, Markus Morgenstern We present an ultrahigh vacuum mask aligner driven by three piezoelectric motors which guide and align a SiN shadow mask under capacitive control towards a conductive sample surface. The three capacitors for read out are located at the backside of the thin mask. The mask can be placed in micrometer distance from the sample surface without touching it, while deliberately keeping it parallel to the sample surface. The sample can additionally be displaced laterally with respect to the mask with a precision of few nanometers. Samples and masks can be exchanged in-situ with a wobble stick. We demonstrate an edge sharpness of the deposited structures below 100 nm, which is likely limited by the diffusion of the deposited Au on Si(111). |
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T70.00047: Characterization of LED Temperature Dependence and Power-Efficient LED Modulation Methods for Use in Fluorescence Absorption Spectroscopy Phillip Kuplic, Lucas J Koerner Temperature characteristics of LEDs impact the performance of optical instruments. We have characterized these effects by powering various colors of high-powered LEDs in constant current mode and analyzing the light output with a spectrometer. Light intensity, center wavelength, and spectral full width at half maximum (FWHM) was recorded as temperature changed, allowing for a better understanding of the relationship between temperature and the characteristics of light. Results show that an increase in temperature (range of 40 °C) decreases the efficiency (average of 15%; peak of 46%), increases the FWHM (average of 6.7%), and causes the center wavelength to shift to the red. Furthermore, we present the impact of sinusoidal current modulation upon the wavelength spread of LEDs. Circuit approaches for power efficient modulation are proposed that minimize changes in LED characteristics and produce pure sine-waves. Temperature characterization measurements and modulation methods are critical for low-cost and portable medical instruments. |
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T70.00048: ENERGY RESEARCH AND APPLICATIONS
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T70.00049: Reducing thermal conductivity through lattice softening Riley Hanus, Matthias Agne, Jeff Snyder Two fundamentally different avenues for controlling a materials thermal conductivity are phonon scattering and lattice softening. Lattice softening recognizes that lattice defects alter the phonon dispersion relation and thus reduce the lattice thermal conductivity (κL) by reducing phonon frequencies and group velocities. I will discuss experimental data on several systems (Si, PbTe, and SnTe) which demonstrate that microstructural defects such as grain boundaries, dislocations, and vacancies can significantly softening a materials lattice, reducing the materials speed of sound. By analyzing the data on elasticity and thermal conductivity through transport modeling, it is shown that lattice softening is a dominate mechanism for the reduction of κL in these systems. Additionally, it will be shown that lattice softening is theoretically expected to be more effective than phonon scattering effects in anharmonic materials and at high temperatures. This work demonstrates how lattice softening is emerging as an important mechanism for controlling a materials thermal conductivity, and provides new avenues to engineer a materials κL, beyond phonon scattering. |
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T70.00050: Near-field radiative heat transfer in the presence of edge states Gaomin Tang, Jian-Sheng Wang We demonstrate that dispersionless electronic edge states substantially enhance near-field radiative heat transfer. An unusual heat flux dependence on vacuum gap separation is found, where the heat transfer can reach local maxima at experimentally feasible gap separation. The underlying mechanisms for the peculiar effects are uncovered from a simple Su-Schrieffer-Heeger model, and we propose zigzag single-walled carbon nanotubes as experimental realizations. Our results offer a novel route to active radiative thermal switch, where the heat flux can be modulated through tuning the presence or absence of edge states. |
(Author Not Attending)
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T70.00051: Thermoelectric Transport at Organic-silicon interface Naiming Liu, Mona Zebarjadi Hybrid organic-inorganic materials are among the latest class of materials proposed for thermoelectric applications. The organic-inorganic interface is critical in determining the effective transport properties of the hybrid material. We present results on the thermoelectric properties of the F4TCNQ-silicon interface. Transfer of electrons from silicon to F4TCNQ results in holes trapped within the screening length of the interface that can move parallel to the interface. We report the response of these trapped charges to applied temperature differential and compare the thermoelectric transport properties of the silicon with and without F4TCNQ. The results confirm the presence of interface charges and demonstrate enhanced interface thermoelectric power factor. |
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T70.00052: First principle study of lithium diffusion pathways in layered oxide Li2La(TaTi)O7 Ming Yu, Selorm Joy Fanah, Ashfia Huq, Farshid Ramezanipour Layered oxides, as the Ruddlesden-Popper family, have the potential to be a good lithium-ion conductor as solid electrolytes for lithium ion batteries. Recently, new family member, the layered Li2La(TaTi)O7 has been successfully synthesized [1] and its ionic conductivity has been examined. Our first principle calculations reveal the orientation of lithium diffusion pathways and the energy barriers in these pathways, which are directly correlated with the atomic arrangement of this material. We also found that the energy barriers will be lowered with Li deficiency, indicating that introducing lithium defects can also improve the lithium diffusion, and therefore the ionic conductivity, agreement with our experimental observations. These results have broad implications with regard to the design of a new class of Li-conducting oxides based on Ruddlesden-Popper oxides. |
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T70.00053: Understanding H-ion transport dynamics in superionic conductor BaH2 Qiangqiang Gu, Feipeng Zheng, Ji Feng Superionic conductors have received increasingly attentions due to the potential applications to energy storage, fuel cells, solid electrolytes, etc. BaH2 was experimentally reported as a superionic conductor which exhibits ionic conductivity of nearly 0.2 S/cm at 630 °C, an order of magnitude larger than that of state-of-the-art proton-conducting perovskites at this temperature[1]. However, the mechanism of H-ion conduction therein still remains investigations. In this work, we use first-principles nudged elastic band (NEB) simulations to compute the energy barriers. The quantum dynamic effects were considered by path-integral Monte Carlo(PIMC) sampling. Free energy surface was calculated using PIMC combined with umbrella sampling method. Furthermore, kinetic Monte Carlo (kMC) simulations were carried out to compute the ionic mobilities and conductivities which match well with the experimental data. |
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T70.00054: Crystallization Dynamics of Amorphous Solid Electrolytes using Large Scale Atomistic Simulations Chris Ablitt, Mordechai C Kornbluth, Jonathan P Mailoa, Boris Kozinsky LiPON ceramic glass electrolytes offer the possibility to increase the energy density of batteries thanks to their resistance to dendrite formation, a problem in batteries using Li-metal anodes, yet the conductivity of oxide glasses is relatively poor. This work studies the fundamental process of amorphization, crystallization, and ion conduction within a wide composition range of lithium phosphate systems. We employ atomistic force fields developed from ab-initio dynamics trajectories and validated on lithium phosphates with comparison to ab-initio trajectories and experimental characterization. Using large-scale dynamics simulations we predict the structural relaxation and conductivity of glass electrolyte materials, reaching timescales and system sizes inaccessible to ab-initio methods. We show how the Li content determines both the ionic conductivity and the degree of corner-sharing, which in turn determines the ease of amorphization and provides insight into optimal glass processing conditions. |
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T70.00055: Photovoltaic and thermoelectric indirect coupling for maximum solar energy exploitation Mohammed HAJJI Advanced photovoltaic devices with a high performance/cost ratio is a major concern nowadays. In the resent study, we investigate the energetic efficiency of a new concept based on an indirect (instead of direct) photovoltaic and thermoelectric coupling. Using state-of-the-art thermal transfer calculations, we have shown that such an indirect coupling is an interesting alternative to maximize solar energy exploitation. In our model, a concentrator is placed between photovoltaic and thermoelectric systems without any physical contact of the three components. Our major finding showed that the indirect coupling significantly improve the overall efficiency which is very promising for future photovoltaic developments. |
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T70.00056: High-performance organic solar cells by adding the third component Yao Wu, Thomas Russell Organic solar cells have attracted much attention over the past decades, which have numerous advantages, including solution-processability, low cost, light weight, and flexibility. Due to the development of non-fullerene acceptors, the efficiencies of organic solar cells were increased to 17% for a tandem junction and 14% for a single junction. To further improve the efficiency of organic solar cells, a third component can be added to the active layer making a ternary blend film. Ternary blend film contains a donor material, an acceptor material, and a third component having complimentary absorption with the donor and acceptor, increasing the light harvesting ability of the devices. Some of the third components have suitable energy levels to reduce the charge transfer barriers between the donor and acceptor. The added component can also induce the crystallization of the donors and change the morphology of the blend film. In our work, a few third components were selected to add in the active layer, which leads to an improvement of the device performance. Also, the absorption, charge transportation and the morphology of the ternary system were carefully investigated to understand how the third component influences the efficiency of organic solar cells. |
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T70.00057: Exploring the Effect of Conduction Band Matching on Solar Cell Voltage and Efficiency for CdSe – Metal Oxide Quantum Dot Solar Cells Sam Ayala, Matthew Becker Liquid Junction quantum dot solar cells were constructed from three sizes of CdSe quantum dots on a variety of metal oxide nanoparticulate substrates. Metal oxides were chosen to closely match their conduction bands with the conduction bands of the CdSe. It was hypothesized that avoiding energy loss due to large differences between the CdSe and metal oxide conduction bands would increase the open circuit voltage and possibly the efficiency of these “band-matched” solar cells. We found that the opposite was true and that the improved electron kinetics due to larger differences in conduction band levels seems to have a larger influence on the efficiency of the cell. |
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T70.00058: Light absorption induced band bending in p-type Cu2(Zn,Sn)(S,Se)4 thin-film photovoltaic cells: local Raman imaging and scanning probe microscopy Juran Kim, Kee-Jeong Yang, Dae-Hwan Kim, Jin-Kyu Kang, William Jo Kesterite-structured Cu2ZnSn(S,Se)4 (CZTSSe) is one of the most promising materials for highly efficient and low-cost thin-film solar cells because of its appropriate optical and electrical properties. The best efficiency of CZTSSe solar cells is 12.6%, which was obtained using a hydrazine process, while the materials used in this study show efficiency of 12.3%. Note that the CZTSSe thin-films were grown by sputtering and subsequent sulfur-selenium treatment. Raman spectroscopy imaging was utilized to measure local built-in voltage and its local composition. According to the surface potential results, we were able to observe upward band bending near grain boundaries, meaning intra-grains take a role as current path by collected electrons. Unlike Cu(In,Ga)Se2, defects in CZTSSe thin-films have deep energy levels, which can be charge carrier recombination center and cannot be suitable for a current path. By measuring surface photo-voltage, we observed the significant changes in energy band bending under illumination, implying the existence of these interfacial states. The main contribution of the research is related to the realization of new way for carrier separation enhancing power conversion efficiency of the kesterite-based thin-film solar cells. |
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T70.00059: Scalable Transparent Metal-polymer Hybrid Metamaterial for Enhanced Greenhouse Effect Tao Li, Yin Gao, Kun Zheng, Yongmei Ma, Xiulan Huai, Ding Ding, Hang Zhang Tailoring the emissivity of optically engineered materials in both the solar and the ambient blackbody radiation wavelength has led to significant day-time radiative cooling. It is conceivable that manipulating the optical spectrums in the opposite way will lead to enhanced greenhouse effect, as demonstrated in current commercial low-emissivity (low-E) window coatings. In this work, based on Mie scattering and the principle of surface plasmon polaritons for enhanced transparency, metallic nanowire/polymer hybrid structures were designed to achieve the goal of enhancing day-time heating. This metal-polymer hybrid metamaterial can enhance solar heating in enclosed environment or reject thermal radiation for energy saving in air-conditioned environment. The resulted metamaterial can reflect the mid-infrared spectrum effectively(~80%) and be transparent(transmittance of about 85%) to sunlight spectrum at the same time. Comparing our metamaterial with commercial low-E glasses, our metamaterial is more transparent in the visible and less emissive in the infrared . In addition, this type of metamaterials is flexible and can be scalable-manufactured with lower cost than that of low-E glasses. |
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T70.00060: Effects of Prolonged Heat Exposure on the Performance Characteristics of Monocrystalline Silicon Photovoltaic Cells Amanda Portoff, Andrew D Venzie, Justin L Smoyer, Paul Quinn Solar energy is a rapidly growing field of study since alternative energy sources, especially those that are renewable and economically feasible, are highly sought after. Silicon photovoltaic cells are the most commonly used type of cell, yet limitations in their efficiency place a restraint on overall effectiveness. The objective of this research was to observe the effects on the performance characteristics of monocrystalline silicon photovoltaic cells after being exposed to high temperatures for fixed periods of time. In particular, we examined the open-circuit voltage, Voc, and short-circuit current, Isc. To observe these changes, the cells were heated at temperatures ranging from 200o C to 280o C for a duration of 20 minutes. An analysis of various IV curves was used to determine changes in performance characteristics of the cells exposed at different temperatures. Our study revealed that this heat exposure yielded a permanent alteration in the performance of the cell. Ultimately, this exposure led to an increase in the overall performance of the monocrystalline silicon photovoltaic cell. Such an increase in performance occurred with existing cells, requiring no significant changes to the manufacturing process. |
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T70.00061: PV converter with greenhouse filter for laser power beaming Andrei Sergeev, Andrew Hewitt, Harry Hier, Christopher Mike Waits Numerous applications, such as robotics and optical networking, can be significantly enhanced by laser power beaming. The proposed PV converter comprises a semiconductor n-p junction cell with back surface reflector and front surface “greenhouse” filter, which traps long wavelength photons with energies below the energy of optical quanta. The greenhouse filter significantly reduces the emission from the device and increases the conversion efficiency. The efficiency improvement is limited by the nonradiative recombination. The greenhouse effect is reduced if nonradiative recombination dominates over the radiative recombination. Taking into account nonradiative recombination and photon leakage of the filter, we investigate photocarrier kinetics and photon management to optimize GaAs PV device architecture, doping, and photon trapping. We also experimentally investigate the greenhouse effect on the dark current characteristics, the short circuit voltage, and efficiency of the PV converter for laser power beaming. |
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T70.00062: Effects in Performance Characteristics of Monoscrystalline Silicon Photovoltaic Cells Exposed to Cryogenic Temperatures Taylor Worthington, Carlos Sosa, Austin Zimmerman, Andrew D Venzie, Justin L Smoyer, Paul Quinn With a global demand for an efficient, renewable energy source, researching the improvement of photovoltaic cells is crucial. While much research is focused on finding new chemical compounds exhibiting photovoltaic effects, silicon photovoltaic cells are still the most widely used and available. In the following research, successive measurements on monocrystalline silicon photovoltaic cells are taken as they are exposed to a temperature of 80 K for an extended period of time. Performance characteristics such as open circuit voltage, Voc, short circuit current, Isc, and fill fraction, FF, are measured while the cell is sealed inside a cryogenic system held in vacuum. Measurements of the cells' characteristics show that the exposure at 80 K permanently affects the performance of the cell when it is tested at low temperatures. This change occurs primarily in Voc, potentially leading to an overall improvement of the performance of the cell at low temperatures. An understanding of this effect will provide further insight into potential avenues to increase photovoltaic performance. |
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T70.00063: Configuration-dependent field effect on horizontal convective heat transfer in a quasi-one-dimensional magnetic fluid Jun Huang, Weili Luo, T. S. Liu We report our study on field effect on horizontal convective heat transfer in a quasi-one-dimensional magnetic fluid in different temperature and field gradients orientation, where the magnetic boy force and the temperature gradient are perpendicular to gravity. Both gravito-thermal and magneto-thermal convections happen when the fields are applied. It was found the magnetic field-induced magneto-thermal flows enhances the gravito-thermal convection when the temperature gradients and field gradients are parallel, and suppresses it when the two gradients are antiparallel, where the single convection roll in zero field was separated into two localized rolls at the two ends of the sample cell. The drastically different flow patterns explain the different field effect on heat transfer in two configurations, which is consistent with the different direction of magnetic body force. It was also found when the field exceed the critical point, the magneto-thermal convections is dominated in the fluids. This novel phenomenon demonstrates new path to energy conversion and important applications in thermal management of electronic device and electric vehicle, and energy transfer devices. |
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T70.00064: Morphology Controlled Electrospun Fibers as the Catalyst Layer for Polymer Electrolyte Membrane Fuel Cells Likun Wang, Guan Hao Chen, Danielle Kelly, Zipei Liu, Audrey Shine, Kao Li, Miriam Rafailovich The efficient operation of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) largely relies on a costly and easily-degradable platinum catalyst layer. Although air spraying techniques has previously served as the main method of catalyst deposition, electrospinning deposition may provide a more promising method by granting users precise control over 3-D structures by manipulating fiber diameter, porosity, and alignment. 12wt% of poly(acrylic acid) (PAA) and Nafion (1:4 weight ratio) solution was used to obtain a semi-viscous base solution for electrospinning. Through Laser Optical Microscopy and Scanning Electron Microscopy, optimal fiber diameter of 1 μm was found when incorporated with Pt/C, allowing uniform catalyst nanoparticles attachment. The fuel cell performance tests indicate that the morphology optimized electrospun electrodes exhibited a 108% increase in max power output over air-sprayed electrodes of comparable loading. This enhancement is attributed to its unique interwoven surface morphology, which increases the specific surface area of electrode and promotes the efficiency of the reactant and proton transport to catalytic sites. Thus, electrospinning can be used as a potential strategy to improve power output of PEMFCs by altering the catalyst electrode morphology. |
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T70.00065: Battery Performance and Reaction Mechanism in Tin Sulfide as Negative Electrode:
First-Principles Calculations Hiroki Kotaka, Hiroyoshi Momida, Ayuko Kitajou, Shigeto Okada, Tamio Oguchi Sodium (Na) ion batteries have been recently expected as a next-generation battery in which Li-ion batteriesis replaced with Na. Tin sulfide (SnS) has beenexpected to have a high energy density and bea candidate for anodematerials of Na-ion batteries. In this study, weinvestigate the battery characteristics of SnS as a negative electrode for Na-ion batteriesby first-principles calculations. We calculate a phase diagram of Na-Sn-S ternary systems from energy analyses, and clarify a possible reaction route considering intermediate products in charge anddischarge reactions. We theoretically estimatethe voltage-capacity curves of Na/SnS half-cell systemsbased on the Na–SnSreaction path obtained from the ternary phase diagram, and compare with the experimental result. From the comparison between calculated and experimental results, the Na2S reaction productcan precipitate in the SnS electrodes after discharging, and it is expected that the electrode can recover to be SnS again after charging. Therefore, the conversion reactions in which Na2S precipitates in the SnS electrodes are consideredto occur reversibly. |
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T70.00066: Structural mechanisms in complex oxides enabling high-rate lithium-ion energy storage Kent Griffith, Kamila Wiaderek, Giannantonio Cibin, Lauren Marbella, Clare Grey The maximum power output and minimum charging time of a lithium-ion battery depend on mixed ionic–electronic conduction. We show that complex niobium tungsten oxides with frustrated polyhedral arrangements and dense μm-scale particle morphologies can rapidly and reversibly intercalate large quantities of lithium. Analysis of high-rate and multi-electron energy storage will be discussed with insights from operando X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and multi-edge X-ray absorption spectroscopy for the recently reported crystallographic shear structure and bronze-like oxide phases[1]. Materials and mechanisms that enable lithiation of μm particles in minutes have implications for high power applications, fast charging devices, all-solid-state batteries, and general approaches to electrode design and materials discovery. |
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T70.00067: Electrochemical kinetics of SEI growth in porous electrodes Supratim Das, Michael Forsuelo, Martin Bazant Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in LIBs. Despite its importance, the fundamental mechanisms remain unclear, primarily because of the complicated reaction pathways involved. SEI growth can be both electrochemical and chemical in nature, and thus, it is a strong function of the potential and degree of lithiation of the electrode. In this work, we model the early-stage and long-term growth of SEI by accurately capturing the potential dependence of its formation kinetics as well as long term rate limiting steps, and validating it against extensive experimental data. This is done using the Multiphase Porous Electrode Theory (MPET) framework on graphite (phase separating) and carbon black (non phase separating) particles. Results indicate that the peak SEI-forming currents are higher for higher driving currents. Counterintuitively, despite higher peak SEI-forming currents, the highest differential capacities or ‘extent of SEI growth’ are seen for lower driving currents, which implies that SEI formation is a stronger function of potential and cycling time, than the driving current. This work holds promise for the predictive design of procedures for manufacture and formation of LIBs. |
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T70.00068: Structure of lithium dendrite in polymer electrolytes Fudong Han, Tiancheng Yi, Robert Gregory Downing, Robert Briber, Chunsheng Wang, Howard Wang The structure of Li dendrites grown in solid polymer electrolytes (SPE) has been studied using a symmetric sandwich cell of Li / poly(ethyleneoxide) (PEO) : lithium bis(trifluoromethane) sulfonamide (LiTFSI) / Li as a model system. In situ neutron depth profiling (NDP) during directional Li pumping and plating shows that dendrites start to grow, and eventually short-circuit the battery. Li dendrite 3D mapping reveals rather heterogeneous lateral distribution of Li over wide length scales from below a millimeter to centimeters. While the lateral mobility of Li appears to be large, most dendrites grow from the plating electrode, with the overall composition decreases linearly from the electrode interface to the bulk of the electrolyte. It is observed that dendrites also grow from the bottom electrode, where presumably only Li oxidation reaction occurs. The revelation poses new design and engineering challenges in using Li metal electrode in future batteries. |
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T70.00069: Flexible Graphene-Carbon Nanotube Supercapacitors Karen Pearson, Vladimir Samuilov, Shi Fu A carbon fiber textile has been utilized as flexible supercapacitor electrodes with cost-effective graphene nanoplatelet composite material (GNP) as model material for coating the electrodes. GNP represent a new class of carbon nanoparticles with very high intrinsic electrical conductivity in plane and accessible surface area. Multi wall carbon nanotube (MWCNT) at the concentration 50:50 of CNT to GNP were added to take advantage of the high surface area of the composite of these two carbon nano-materials. |
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T70.00070: Applying a 1D Plasma Profile Simulator to COMPASS to Model Sawtooth Instabilities Martin Liza Being able to control the plasma state and its evolution in real time is crucially important for the confinement stability. However, the complex physics that needs to be solved requires a high amount of computational power. |
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T70.00071: Computational fluid dynamics modeling of a microchannel-type reactor for the coupling of OCM and reforming reactions Myung-June Park, Minji Son, Hae Lin Yang, Seon-Ju Park, Yun-Jo Lee Oxidative coupling of methane (OCM) is a reaction that converts methane to high-value added ethylene and ethane. However, strong exothermic heat of reaction leads to thermally unstable operation and lowers the selectivity of the desired species. To control the heat of OCM, we developed a microchannel-based reactor that couples OCM with the steam reforming of methane (SRM), one of strong endothermic reactions. |
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T70.00072: Raman Spectroscopy of Diesel and Gasoline Engine-Out Soot Zhipeng Ye, Haiwen Ge, Rui He We studied engine-out soot samples collected from a heavy-duty direct-injection diesel engine and a port-fuel injection gasoline spark-ignition engine. The two types of soot samples were characterized using Raman spectroscopy with different laser power. A Matlab program using least-square-method with trust-region-reflective algorithm was developed for curve fitting. We used a DOE (design of experiments) method to avoid local convergence. This method was used for two-band fitting and three-band fitting. The fitting results were used to determine the intensity ratio of D and G Raman bands. We find that high laser power may cause oxidation of soot samples, which gives higher D/G intensity ratio. Diesel soot has consistently higher amorphous/graphitic carbon ratio and thus higher oxidation reactivity, in comparison to gasoline soot, which is reflected by the higher D/G intensity ratio in Raman spectra measured under the same laser power. |
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T70.00073: Fundamentals of the photocatalytic activity of conjugated polymers for hydrogen evolution reaction: optical and thermodynamic aspects Giane Damas, Cleber F. Marchiori, C. Moyses Araujo Harvesting sunlight is a convenient approach to meet the global demand of energy, a process that makes use of a suitable photo-electro-catalyst to convert solar energy into chemical fuels[1]. In this context, conjugated polymers have emerged as a subclass of materials with potential applicability as photocatalysts for hydrogen evolution reaction (HER). [2] In this work, we use density functional theory-based methods to evaluate the thermodynamic and optical properties of a set of conjugated polymers containing fluorene, cyclopenthathiophene or thiophene-based donor units and benzothiadiazole-based acceptor units. Optimizations and frequencies were held in Gaussian 09 [3] at the M06/6-31G* level of theory, whereas the excitation, solvation and electronic energies were obtained with the 6-311G** basis set. Our preliminary results show that the polymers containing benzo(triazole-thiadiazole) or benzo(triazole-selenodiazole) acceptor units present a broad absorption spectrum and a suitable reduction potential for photocatalytic HER. In particular, PFO-DSeBTrT has maximum peak at 950 nm, while showing a hydrogen binding free energy (0.02 eV) that is lower in absolute values than Pt (-0.10 eV). |
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T70.00074: ELDOR-detected NMR Spectroscopy at 115/230 GHz Zaili Peng, Susumu Takahashi Electron-electron double resonance (ELDOR)-detected NMR (EDNMR) spectroscopy is one type of the EPR based hyperfine spectroscopy techniques, which is used to detect hyperfine couplings between magnetic nuclei and unpaired electrons, which are too small to be resolved in the conventional EPR spectrum. Compared with other commonly used hyperfine spectroscopy, for instance, ESEEM (electron spin echo envelop modulation) and ENDOR (electron nuclear double resonance), HF EDNMR has advantages of higher sensitivity and finer spectral resolution enabling high-resolution hyperfine spectroscopy at room temperature. In this presentation, we present the principle and implementation of EDNMR in our 115/230 GHz EPR spectrometer at USC, and demonstrate the strategies to obtain high quality EDNMR spectrum by the employment of EDNMR on a standard sample. In addition, we discuss applications of HF EDNMR on the study of solid-state spin systems. |
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T70.00075: TOPOLOGICAL MATERIALS
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T70.00076: Floquet generation of higher order topological phases and its quenching dynamics Tanay Nag, Vladimir Juricic, Bitan Roy We discuss a non-equilibrum Floquet scheme to generate the higher-order topological (HOT) phases. In particular, we find that if a d-dimensional regular topological phase involves m Hermitian matrices then a kick in the discrete symmetry breaking Wilsonian mass term, which is composed of additional p-1 anti-commuting matrices, can give rise to nth order Floquet HOT phases (with n=1,...,p). We demonstrate explicitly this mechanism in the cases of three-dimensional spin-1/2 Dirac semimetal, 2nd order topological insulator and nodal loop semimetal. We give analytical support for the numerical findings by using the Floquet effective Hamiltonian. Additionally, we study the relaxation dynamics of the above phases by calculating the survival probability for a topological phase followed by a sudden quench. Our results suggest that survival probability for quenching from a higher-order to a lower-order phase depends on the system size while the reverse quenching does not show any system size dependence. |
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T70.00077: Edge states across the topological phase transition due to approximate chiral symmetry in quantum anomalous and spin Hall systems Denis Candido, Maxim Kharitonov, Carlos Egues, Ewelina Hankiewicz In this work we demonstrate that a quantum anomalous Hall system (Chern |
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T70.00078: Observation of multiple Dirac states in EuMg2Bi2 Firoza Kabir, Md Mofazzel Hosen, Fairoja Cheenicode-kabeer, Alex Aperis, Gyanendra Dhakal, Klauss Dimitri, Christopher Sims, Sabin Regmi, Tomasz Durakiewicz, Peter Oppeneer, Dariusz Kaczorowski, Madhab Neupane Initiated by the discovery of topological insulators, topologically non-trivial materials especially topological semimetals and metals have emerged as a new frontier in the field of quantum materials. In this work, we perform a systematic measurement of EuMg2Bi2, a compound with antiferromagnetic transition temperature at 7K. By utilizing angle-resolved photoemission spectroscopy in concurrence with first principle calculation, we observe Dirac cones at the corner and the zone center of the Brillouin zone. From our experimental data odd number of Dirac states are observed per Brillouin zone. Our experimental investigation of detailed electronic structure of EuMg2Bi2 could potentially provide the platform to study the interplay between topology and magnetism. |
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T70.00079: Tunable Topological Phase Transition in 2D Heterostructures Anh Pham, Panchapakesan Ganesh Two dimensional (2D) materials can host a wide range of properties, such as magnetism [1], high mobility and a wide range of topological properties [2]. Recently, it has been experimentally shown that heterostructures of 2D materials can be synthesized. This leads to the exciting possibility of interfacing 2D materials in heterostructure geometries to design new and exotic quantum-materials for dissipationless quantum-transport. In this study, we theoretically demonstrate that vertical heterostructures of magnetic and topological 2D materials can give rise to quantum anomalous Hall (QAH) effect. In addition, we show that electric-fields can be used to tune the interfacial coupling to drive the system to the QAH regime. We demonstrate this concept in 2D heterostructures such as CrI3/Sb/CrI3, CrI3/Si/CrI3, and CrI3/Ge/CrI3. |
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T70.00080: Two-Step Growth Method for High Quality (Bi0.5Sb0.5)2Te3 and Cr doped (Bi0.5Sb0.5)2Te3 on Nb surfaces for Topological Josephson Junctions He Ren, Hui Zhang, Xiaodong Ma, Deler Langenberg It has been theoretically predicted that Majorana bound state can appear at the interface between topological insulators and superconductors. To obtain high quality (Bi0.5Sb0.5)2Te3 films on superconducting Nb surface, a two-step growth method was developed to promote proper (Bi0.5Sb0.5)2Te3 film nucleation on Nb surfaces in the early growth stage, where Bi, Sb and Te clusters were firstly evaporated at a relatively low temperature and then annealed to form a crystalized passivation layer, and a standard (Bi0.5Sb0.5)2Te3 film was grown under the normal deposition temperature secondly. Based on the two-step method, we also grew high quality Cr doped Bi-Sb-Te films on Nb surface with a similar procedure. Reflection high-energy electron diffraction (RHEED), high resolution transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to characterize the quality of the films. Finally, a top Nb film was deposited by magnetron sputtering at the room temperature. The Hetero-Nb/epitaxial (Bi0.5Sb0.5)2Te3 (with and without Cr doped)/ Nb stacks were further fabricated into micro Josephson junctions and the results of transport measurement also demonstrate a good quality of the multi-layer stacks. |
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T70.00081: Magnetic Weyl Points and Symmetry Protected Nodal Loops in 5d Cubic Double Perovskites Young-Joon Song, Kwan-Woo Lee 5d systems show abundant physical phenomena due to an interplay between strong spin-orbit coupling (SOC) and moderate correlation, vz. the Dirac-Mott metal-insulator transitions in Os-based oxides. In topological characters, various symmetries, SOC, and (sometimes) strength of correlation are key ingredients to generate topologically nontrivial phases. |
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T70.00082: Thermoelectric Imaging of Domain Boundary States in Epitaxial Graphene Sanghee Cho, Yong-Hyun Kim, Ho-Ki Lyeo We investigated electronic states associated with the boundary structure between domains of two carbon layers in epitaxial graphene. The topological structure formed between AB and BA stacking domains could be observed in microscopic thermoelectric measurements down to the atomic length scale. Measurements show that the boundary structure observed from epitaxial bilayer graphene is associated with point defects of carbon pentagon-heptagon and the structure forms a closed loop. Such structural patterns define soliton-like domain walls driven by strain in epitaxial graphene, which gives rise to prominent contrast in the thermoelectric measurement. The contrast observed over the domain walls in the measurement of thermoelectric response is the direct consequence of chiral boundary modes expected for tensile-strained boundaries, which is similar to the structures observed in exfoliated and CVD-grown bilayer graphene. These results will help to elucidate how the topological band plays in epitaxial graphene. |
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T70.00083: Bulk and surface states carried supercurrent in ballistic Nb-Dirac semimetal Cd3As2 nanowire-Nb junctions Caizhen Li, Chuan Li, Lixian Wang A three dimensional Dirac semimetal has bulk Dirac cones in all three momentum directions and Fermi arcs like surface states, and can be converted into a Weyl semimetal by breaking time-reversal symmetry. However, the highly conductive bulk state usually hides the electronic transport from surface state in Dirac semimetal. Here, we demonstrate the supercurrent carried by bulk and surface states in Nb-Cd3As2 nanowire-Nb short and long junctions, respectively. For the ~1μm-long junction, the Fabry-Pérot interferences-induced oscillations of the critical supercurrent are observed, suggesting the ballistic transport of the surface states carried supercurrent, where the bulk states are decoherent and the topologically protected surface states still stay coherent. Moreover, a superconducting dome is observed in the long junction, which is attributed to the enhanced dephasing from the interaction between surface and bulk states as tuning gate voltage to increase the carrier density. The superconductivity of topological semimetal nanowires is promising for brading of Majorana fermions toward topological quantum computing. |
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T70.00084: Gate-tuned Aharonov-Bohm interference of surface states in a quasiballistic Dirac semimetal nanowire Benchuan Lin, Shuo Wang, Zhi-Min Liao, Dapeng Yu We report an observation of a topologically protected transport of surface carriers in a quasiballistic Cd3As2 |
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T70.00085: Fano Interference between Bulk and Surface States of a Dirac semimetal Cd3As2 nanowire Shuo Wang, Benchuan Lin, Zhi-Min Liao, Dapeng Yu Dirac semimetals possess Fermi-arc surface states, which will be a set of discrete surface subbands in a nanowire due to the quantum confinement effect. Here, we report a tunable Fano effect induced by the interference between the discrete surface states and continuous bulk states of a Dirac semimetal Cd3As2 nanowire. The discrete surface bands lead to a zero bias peak in conductance as the Femi level is tuned to across the surface subbands. The Fano resonance results in an asymmetric line shape in the differential conductance dI/dV spectrum. Furthermore, the Fano interference would introduce an additional phase into the Weyl orbits and lead to a modification of the oscillation frequency. The results are valuable for further understanding the exotic quantum transport properties of topological semimetals. |
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T70.00086: Observation of Dirac States in Superconducting Materials Klauss Dimitri, Md Mofazzel Hosen, Gyanendra Dhakal, Hongchul Choi, Firoza Kabir, Christopher Sims, Dariusz Kaczorowski, Tomasz Durakiewicz, Jian-Xin Zhu, Madhab Neupane The massive shift in interest towards Topological Superconductors (TSC) and their potential to host Majorana fermions has been a major point that connects the rhetoric of both quantum computation and topological materials. Following this narrative, superconducting Pd-Bi binaries have large spin orbit coupling strength and can develop a TSC phase peaking the interests of both fields. Here, we report a high-resolution angle-resolved photoemission spectroscopy (ARPES) study on the normal state electronic structure of superconducting α−PdBi2 (Tc=1.7 K). Our results show the presence of Dirac states at higher-binding energy with the Dirac point 1.26 eV below the chemical potential at the zone center. Furthermore, the ARPES data indicate multiple band crossings at the chemical potential, consistent with the metallic behavior of α−PdBi2. Our experimental studies are complemented by first-principles calculations, revealing the presence of surface Rashba states in the vicinity of the chemical potential. Our study extends to other superconducting materials providing an opportunity to investigate the relationship between superconductivity and topology. |
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T70.00087: Dynamical correlation functions and the related novel physical effects in 3D topological semimetals Jianhui Zhou, Hao-Ran Chang, Di Xiao, Hong Guo We present a unified derivation of the dynamical correlation functions including density-density, density-current and current-current, of 3D Weyl/Dirac semimetals by use of the Passarino-Veltman reduction scheme at T=0K. The generalized Kramers-Kronig relations with arbitrary order of subtraction are established to verify these correlation functions. Our results lead to the exact chiral magnetic conductivity and directly recover the previous ones in several limits. We also investigate the magnetic susceptibilities, the orbital magnetization, and briefly discuss the impact of electron interactions on these physical quantities within the random phase approximation. Recently, we develop a guage invariant theory of chiral magnetic plasmons and discuss the impact of the chiral anomaly. Our work provides a starting point for the investigation of the nonlocal transport and optical properties due to the higher-order spatial dispersion in 3D Weyl/Dirac semimetals. |
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T70.00088: Hydrothermal Synthesis of Tellurium Nanoflakes with Post Growth Thinning Anne Herbert, Asu Rolland, Giriraj Jnawali, Iraj Abbasian Shojaei, Samuel M Linser, Anjaly Nanattuchirayil, Peng Zhang, Howard E Jackson, Leigh Smith, Ruoxing Wang, Gang Qiu, Wenzhuo Wu, Peide (Peter) Ye Tellurium is a hexagonal chiral crystal with covalently bonded left- or right-spiral chains of atoms along the c-axis, with much weaker van der Waals interactions between the chains. The lowest conduction bands exhibit Weyl node crossings with different chiralities at the H and H’ points in the Brillouin zone. We synthesize 40 nm-thick Tellurium nanoflakes via the hydrothermal method, and confirm the quality of our samples with Raman spectroscopy. The flakes were thinned through a basic NaOH- solution with acetone. Thicknesses was measured with Raman spectroscopy, via peak shift, and confirmed using atomic force microscopy. |
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T70.00089: Electronic structure and optical responses of chalcopyrite semiconductors ZnSnX_2
(X = P, As, Sb) Banasree Sadhukhan Ternary compounds having the chalcopyrite structure are of considerable interest because of their semiconducting, electrical, structural, mechanical and nonlinear optical properties. Chalcopyrite semiconductors ZnSnX_2 (X = P, As, Sb) lack an inversion symmetry. Under strong light irradiation, the noncentrosymmetric material exhibits photocurrents as nonlinear |
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T70.00090: Angle-resolved photoemission spectroscopy study of the topological Kondo insulator candidates CeRhX (X=As, Sb) Seungho Seong, Kyoo Kim, Eunsook Lee, Chang-Jong Kang, Taesik Nam, Byung Il Min, Takenobu Yoshino, Toshiro Takabatake, Jonathan Denlinger, Jeongsoo Kang Topological Kondo insulators (TKIs) belong to a class of symmetry-protected topological phases arising from the strong correlation. CeNiSn, CeRhSb, and CeRhAs are known as Kondo insulators with the large anisotropy [1]. Recently CeNiSn and CeRhSb are predicted to be the novel TKIs having the Möbius-twisted surface states [2]. A unique feature in these systems is the non-symmorphic glide and screw axis symmetries, which bring about the new topological surface band structures. We have investigated the electronic structure of CeRhX (X=Sb, As) employing ARPES and DFT/DMFT band calculations. The Fermi surfaces (FSs) and band structures are successfully measured for the three orthogonal crystallographic directions. For X=Sb, the metallic FSs are obtained for all three different planes. Both the FSs obtained at the Ce 4f resonance and the ARPES data are described well by the unfolded DFT FSs and the DMFT band structures, respectively. The temperature-evolution of the Ce 4f peak agrees with that of the Ce 4f Kondo resonance. The photon energy map provides evidence for the 3D character of the Fermi-edge states unlike the theoretically predicted surface states. |
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T70.00091: Discovery of topological nodal-line fermionic phase in a magnetic material GdSbTe Sabin Regmi, Md Mofazzel Hosen, Gyanendra Dhakal, Klauss Dimitri, Pablo Maldonado, Alex Aperis, Firoza Kabir, Christopher Sims, Peter Riseborough, Peter Oppeneer, Dariusz Kaczorowski, Tomasz Durakiewicz, Madhab Neupane
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T70.00092: Observation of Nodal Loops in HfP2 Christopher Sims, Md Mofazzel Hosen, Gyanendra Dhakal, Hugo Aramberri, Klauss Dimitri, Firoza Kabir, Dariusz Kaczorowski, XIAOTING ZHOU, Tay-Rong Chang, Hsin Lin, Nicholas Kioussis, Madhab Neupane Topological nodal-line semimetals that arise due to band touching which are protected by crystalline symmetries are materials that are currently being pushed to further understand topology in crystals protected by different symmetries. Here we report the experimental observation of three topological nodal loops in the transition metal pnictide HfP2 using angle resolved photoemission spectroscopy. Our systematic study reveals the detailed electronic structure of HfP2 which is protected by glide symmetry. Our calculations reveal three unique nodal loops, one of which is protected by glide symmetry in the center and two non-trivial topological nodal loops in finite k-space. Our experimental data and calculations both reveal the existence of these non-trivial loops which warrants further symmetry analysis in the non-symmorphic space group. |
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T70.00093: Temperature-dependent coherent phonon dynamics in Bi2Te3 Tsun-I Chen, Jin-Wei Li, Hsuan-Yin Chen, Jung-Chun Huang, Meng-Qing Lee, Chao-Kuei Lee In this work, temperature-dependent(78K~290K) coherent phonon dynamics in topological insulator Bi2Te3 are investigated. Four coherent phonon types(A1g1, A1g2, Eg, coherent acoustic phonon) with strong temperature dependency are observed in transmission pump-probe spectroscopy at low temperature(78K, 90K).These could be attributed to temperature dependent gradient force which resulting in the coherent phonons generation. Especially, lifetime of around 2.87ps for Eg phonon mode is observed for the first time.The depressing signal of reflective pump probe due to the enhancing absorption of surface state for thin film topological insulator will be accordingly increasing as temperature cooling is proposed. |
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T70.00094: Optical nonlinearity investigation of Bi2Te3 Meng Yu Wu, Meng-Yuan Chuang, Wei-Heng Sung, Peng Lee, Jun-Peng Qiao, Chao-Kuei Lee To realize 2-D material nonlinear optical applications, including wavelength generation, ultrafast optical processing, and saturable absorber for ultrafast laser, the information of optical nonlinearity property for given material is very important. In this work, ultra-low peak intensity (103 to 105 W/cm2) z-scan measurement was proposed and buildup for studying the discontinuity of conventional nonlinear transmission with low and high pulse energy. The two photon absorption behavior was observed and is with tremendous large coefficient of 2.03x10-2 cm/W for excitation power of 100uW. This can be used to interpret and resolve the discontinuity. |
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T70.00095: Modulation of the universal conductance fluctuations by broken time-reversal symmetry in topological insulator Shuai Zhang, Fengqi Song In topological insulator BiSbTeSe2 nanowire device, we extract the conductance fluctuations and study their magnetic field dependence in the gate-dependent transport of topological electrons. With the magnetic field increasing, the conductance fluctuation magnitudes are found to reduce by a ratio of √2 and form a quantized step, and this is observed both in n-type and p-type transport. This is related to the breaking of the time reversal symmetry of three-dimensional topological insulators, which reveal a crossover of the symmetry classes. |
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T70.00096: Magnetoresistance from Quantum Interference Effects in Topological Materials Bo Fu, Huanwen WANG, Shunqing Shen A large amount of experimental results about the longitudinal magnetoresistance (LMR) in Weyl semimetal and topological insulator systems display a nonmonotonic behavior over a wide range of magnetic field conditions. At small fields close to zero, a sharp increase of the LMR is observed. When the magnetic field exceeds some threshold value, the LMR is found to decrease as the magnetic field increases. In experiment, this crossover from positive to negative magnetoresistivity is commonly attributed to the competition between Chiral anomaly and weak antilocalization. This negative magnetoresistivity is viewed as the signature of chiral anomaly and the evidence for the existence of Weyl fermion. Using the Feynman diagram techniques, we derive the magnetoconductivity formulae from the quantum interference effects for disordered three-dimensional Dirac materials. By including all the possible contributing Cooperon modes, we can reproduce such nonmonotonic magnetoresistance behavior. We also find that by changing the chemical potential, topological trivial and non-trivial insulators exhibit distinctly different magnetoconductivity behavior. It can help us to directly distinguish the different topological phases through the bulk states transport measurement. |
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T70.00097: Compressibility of the quantum spin Hall insulator HgTe Matthieu Dartiailh, Simon Hartinger, Alexandre Gourmelon, Hugo Bartolomei, Jean-Marc Berroir, Hartmut Buhmann, Laurens W Molenkamp, Bernard Plaçais, Erwann Bocquillon Quantum spin Hall (QSH) insulators are two-dimensional electron systems which host spin-polarized edge states while the bulk remains insulating. These helical edge states provide a potential support system to encode information in ‘topological quantum bits’ robust to the decoherence. Despite immense theoretical and experimental efforts, the rise of these new materials has however been hampered by strong difficulties to clearly observe their predicted topological properties. These challenges motivate the investigation of the dynamics of their topological edge states using microwave techniques. |
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T70.00098: Vertical Topological Josephson Junciton Yutong Dai, Guoxing Miao Topological Josephson junciton holds a promising platform for pursuiting Majorana zero mode. Due to the proximity effect, the topological insulator layer sandwiched by two superconducting layers can be considered as topological superconductor. We explored the Andreev bound states of this heretrostructure, and observed teh 2pi peroidic Andreev states, arising from the paring potential in topological superconductor. We also calculated the transport properties and compared simulation results with experimental measurements. |
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T70.00099: ABSTRACT WITHDRAWN
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T70.00100: ABSTRACT WITHDRAWN
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T70.00101: WITHDRAWN ABSTRACT
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T70.00102: Generalized Lieb-Schultz-Mattis theorem on bosonic symmetry protected topological phases SHENGHAN JIANG, Yang Qi, Yuan-Ming Lu We propose and proof a generalized Lieb-Schultz-Mattis (LSM) theorem for symmetry protected topological (SPT) phases on boson/spin models in any dimensions. The "conventional'' LSM theorem, e.g. spin-1/2 per unit cell on square lattice, disallows symmetric short-range-entangled (SRE) phase. Here, we focus on systems with fractional spins, but have no LSM anomaly. Thus, it is possible to have symmetric SRE phases in the long wavelength. We show that, symmetric SRE phases obtained in these systems must be nontrivial SPT phases of both on-site and spatial symmetries. Depending on models, they can be either strong or higher-order SPT phases, characterized by nontrivial edge/corner states. Furthermore, given global symmetry group and fractional spins, we are able to determine all possible SPT phases by using a spectral sequence expansion of group cohomology. We also provide examples in various dimensions, and discuss possible physical realization of these SPT phases based on topological defects/quasiparticles condensation picture. |
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T70.00103: Charge-spin response and collective excitations in Weyl semimetals Sayandip Ghosh, Carsten Timm We present analytical expressions for all components of the frequency- and wave-vector-dependent charge-spin |
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T70.00104: Non-linear optical response and HHG in 3D Dirac semimetals Jeremy Lim, Yee Sin Ang, Lay Kee Ang Attosecond-duration pulses of extreme ultraviolet to X-ray light, generated via high harmonic generation (HHG), have proven to be highly useful tools in the study of the smallest and quickest fundamental phenomena. The study of HHG in condensed matter systems has attracted much interest due to its potential to realize novel solid-state optical technologies, as well as greater brightnesses compared to gas-phase HHG. We will present results on high harmonic generation in topological materials like 3D Dirac and Weyl semimetals, which exhibit strong, non-linear response to incident fields, which result in efficient generation of odd harmonics. We consider the massless Dirac quasiparticle limit, previously used to predict the harmonic spectra of 2D graphene due to its simplicity and physical transparency, and extend it to 3D Dirac semimetals. We study its non-linear response due to incident fields, and predict its harmonic spectra. A comparison of our results with graphene as well as potential novel photonic applications will be discussed. |
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T70.00105: Probing Weyl nodes by inelastic neutron scattering Michael Bjerngaard, Bogdan Galilo, Ari Mark Turner We present how to detect Weyl nodes in a material by inelastic neutron scattering, taking into account realistic anisotropic properties. A generic material will not have relativistic symmetry. However, under circumstances not too limiting, the dynamics of the excitations can be mapped to a relativistic symmetry. It is then possible to separate out universal properties reflecting this in the cross-section. In a fully unpolarized experiment it is possible to detect the spin-momentum locking of Weyl states, their linear dispersion, principal axis and a sum-rule independent of the material parameters. Furthermore, with polarized neutrons, it is possible to experimentally control the momentum and spin of the excited Weyl particle-hole pairs, with the consequence that the scattered neutron beam is fully polarized in a direction determined by the coupling parameters of the material. This allows one to determine cleanly the coupling parameters as well as to measure the chirality of the Weyl nodes involved in the scattering. |
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T70.00106: Solutions to the Chiral Fermion Problem from Topological Orders and Floquet Non-Hermition Field Integrals Michael DeMarco, Xiao-Gang Wen Defining a chiral gauge theory non-perturbatively on a lattice has posed a longstanding issue for a non-perturbative definition of the standard model. However, recent insights connecting quantum anomalies with topologically ordered states have led to a breakthrough in lattice formulations of chiral gauge theories: any anomaly-free chiral gauge theory may be formulated as the edge theory of a 2+1 slab with topogical order that is reduced to trivial order by interactions. We keep the `width' of the sla finite so that the system is truly 1+1d. We can then develop a recipe for defining chiral gauge theories that can be extended to higher dimensions. In a parallel development, our recent formulations of discrete-time field integrals allow us to formulate several chiral Floquet phases as local field integrals in discretized spacetime. Intriguingly, these field integrals have unitary correlation functions, even though their Lagrangians are non-Hermitian operators. This provides a second non-perturbative definition of a chiral field theory in 1+1d, with possible generalizations to higher dimensions. |
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T70.00107: ABSTRACT WITHDRAWN
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T70.00108: Quantum criticality preempted by nematicity Shixin Zhang, Shao-Kai Jian, Hong Yao Exotic physics often emerges around quantum criticality in metallic systems. Here we explore the nature of topological phase transitions between 3D double-Weyl semimetals and insulators (through annihilating double-Weyl nodes with opposite chiralities) in the presence of Coulomb interactions. From renormalization-group (RG) analysis, we find a non-Fermi-liquid quantum critical point (QCP) between the double-Weyl semimetals and insulators when artificially neglecting short-range interactions. However, it is shown that this non-Fermi-liquid QCP is actually unstable against nematic ordering when short-range interactions are correctly included in the RG analysis. In other words, the putative QCP between the semimetals and insulators is preempted by emergence of nematic phases when Coulomb interactions are present. We further discuss possible experimental relevance of the nematicity-preempted QCP to double-Weyl candidate materials HgCr$_2$Se$_4$ and SrSi$_2$. |
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T70.00109: WITHDRAWN ABSTRACT
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T70.00110: How to braid mobile with immobile non-Abelian anyons in a topological superconductor Anton Akhmerov, Carlo W J Beenakker, Paul S Baireuther, Inanc Adagideli, Yaroslav Herasymenko Majorana zero-modes in a superconductor are midgap states localized in the core of a vortex or bound to the end of a nanowire. They are anyons with non-Abelian braiding statistics, but when they are immobile one cannot demonstrate this by exchanging them in real space and indirect methods are needed. As a real-space alternative, we propose to use the chiral motion along the boundary of the superconductor to braid a mobile vortex in the edge channel with an immobile vortex in the bulk. The measurement scheme is fully electrical and deterministic: edge vortices ($\pi$-phase domain walls) are created on demand by a voltage pulse at a Josephson junction and the braiding with a Majorana zero-mode in the bulk is detected by the charge produced upon their fusion at a second Josephson junction. |
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T70.00111: Higher-order topological superconductivity: possible realization in Fermi gases and Sr2RuO4 Zhigang Wu, Zhongbo Yan, Wen Huang We propose to realize second-order topological superconductivity in bilayer spin-polarized Fermi gas superfluids. We focus on systems with intralayer chiral p-wave pairing and with tunable interlayer hopping and interlayer interactions. Under appropriate circumstance, an interlayer even-parity s- or d-wave pairing may coexist with the intralayer p-wave. Such mixed-parity phases do not carry one-dimensional gapless Majorana modes on the boundary, but could support Majorana zero modes at the corners of the system geometry, the end points of superconducting domain walls, as well as certain bulk defects. We show how the number and location of the Majorana zero modes can be tuned by the interlayer pairing and hopping. Generalized to spinful systems, we further propose that the putative p-wave superconductor Sr2RuO4, when placed under uniaxial strains, may also realize the desired topological phase. |
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T70.00112: Principal component analysis of quantum Hall wave functions Hengxi Ji, Na Jiang, Xin Wan The fractional quantum Hall effect demonstrates the robustness of topological properties in many-body systems. The effect of mass and interaction anisotropy can be understood in terms of a geometrical description. We present a study of the evolution of quantum Hall wave functions with interaction anisotropy by a statistical learning technique known as the principal component analysis (PCA). We show that the topological and geometrical aspects of a family of wave functions can be readily separated by the PCA. We discuss how to use the PCA to extract wave function metric and to determine the stability of a fractional quantum Hall phase. |
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T70.00113: WITHDRAWN ABSTRACT
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(Author Not Attending)
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T70.00114: Composite Fermion Insulator in Opposite-Fields Quantum Hall Bilayers Yahui Zhang We consider a quantum Hall bilayers from opposite magnetic fields close to the filling 1/2 + 1/2 . We add inter-layer repulsive interaction starting from two decoupled Composite Fermion Liquids (CFL) with opposite chiralities. In this case physical exciton is frustrated from condensation, unlike the conventional quantum Hall bilayers. We argue that more natural phases are the exciton condensates between composite fermions or between slave bosons. The resulting states are insulators with neutral Fermi surfaces coupled to an emergent U(1) gauge field without Chern-Simons term. This insulating state is a generalization of the well-known CFL state. We also comment on the possibility of a topological superconductor in this system. Finally we give experimental proposals to simulate this novel system in a graphene moire system consisting of two nearly flat bands with opposite Chern numbers 1 and -1. |
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T70.00115: Quantum Hall stripes with a reduced transport anisotropy at half-filled Landau levels in GaAs quantum wells Michael Zudov, Xiaojun Fu, Qianhui Shi, Geoffrey Gardner, John Watson, Michael Manfra, K. W. Baldwin, Loren Pfeiffer, Kenneth West It is well known that the hard (easy) resistance due to formation of quantum Hall stripes in high Landau levels of a two-dimensional electron gas exhibits a maximum (minimum) at half-integer filling factors. Here, we report the opposite behavior, namely a local minimum (maximum) in the hard (easy) resistance at half-filling. This talk will discuss our experimental observations in several samples including the temperature dependence of the resistance anisotropy and the response to the in-plane magnetic field applied parallel or perpendicular to the native stripes. |
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T70.00116: SEMICONDUCTORS, INSULATORS, AND DIELECTRICS
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T70.00117: Diamond magnetic sensing and imaging Abdelghani Laraoui, Ilja Fescenko, Janis Smits, Nazanin Mosavian, Joshuat Damron, Nate Ristoff, Pauli Kehayias, Andrey Jarmola Diamond magnetic sensing has emerged as a powerful tool to detect nanomagnetism in biological and solid-state samples, as well to measure weak signals from nuclear spins and spin textures of molecules. We report ongoing experiments that explore several applications of diamond magnetic sensing. These include: (i) microfluidic nuclear magnetic resonance spectrometer capable of sensing small quantities (< 1 pL) of analyte [1], achieving spectral resolutions capable of distinguishing proton with heteronuclear J splittings; (ii) a wide-field magnetic microscope able to measure the stray magnetic fields produced by individual malarial hemozoin biocrystals (size < 300 nm) [3] and magnetization relaxation of single magnetic nanoparticles (size < 25 nm) at room temperature and as a function of applied field up to 350 mT. [1] P. Kehayias*, A. Jarmola*, N. Mosavian, I. Fescenko, F. M. Benito, A. Laraoui, J. Smits, L. Bougas, D. Budker, A. Neumann, S. R. J. Brueck, V. M. Acosta, Nature Commu. 8, 188 (2017). [2] I. Fescenko, A. Laraoui, J. Smits, N. Mosavian, P. Kehayias, J. Seto, L. Bougas, A. Jarmola, V. M. Acosta, arxiv:1808.03636 (2018). |
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T70.00118: Magnetic noise due to interactions between bulk impurities and electrons in nitrogen vacancy center diamonds Bruce Barrios, Shou Li, D H Santamore Nitrogen Vacancy (NV) Centers diamond present great interest as robust atomic-scale magnetic field sensors. One of the serious problems of NV center diamond devices is electric and magnetic field noise. The noise causes ODMR line-broadening, which reduce sensitivity of the devices. In this work we theoretically study the magnetic field noise caused by the magnetic dipole-dipole interactions between the impurities of carbon-13 and nitrogen-14 and the electron in the NV center. We use the cluster correlation expansion method to calculate the magnetic field fluctuations, and then, obtain the noise spectrum. The noise is greater at lower frequencies but rapidly decrease at higher frequencies. |
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T70.00119: Interfacial treatment of 4H SiC/SiO2 interface by shallow boron ion implantation Md. Haider Shaim, Hani Elsayed-Ali Shallow boron ion implantation at the 4H SiC/SiO2 interface was performed using boron multicharged ions from laser plasma. A Q-switched Nd:YAG laser (wavelength 1064 nm, pulse width 7 ns, and fluence 135 J/cm2) was used to ablate a boron target generating a dense plasma source of multicharged ions. Ions up to B5+ are generated. The ions are deflected by an electrostatic field to separate them from the neutrals. SRIM simulation was used to estimate the ion penetration depth in the SiC substrate. The optical bandgap of the 4H SiC was reduced by boron ion implantation. Several MOSCAP devices were fabricated. High-low C-V measurements were used to characterize the MOSCAPs. Shallow boron implantation in the SiC/SiO2 interface reduces the flatband voltage from 4.5 V to 0.04 V. |
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T70.00120: Noble gas defects in ZnO: interaction with the localized defect states Oleksandr Malyi, Kostiantyn Sopiha, Clas Persson Owing to fully occupied orbitals, noble gases are often considered to be chemically inert and to have limited effect on materials properties under typical synthesis conditions. However, using first-principles calculations, we show that the insertion of noble gases (i.e., He, Ne, and Ar) in ZnO results in destabilization of electron density of the material driven by minimization of the unfavorable overlap of atomic orbitals of noble gases and its surrounding atoms. Specifically, the noble gas defect (interstitial or substitutional) in ZnO pushes electron density of its surrounding atoms away from its vicinity. Simultaneously, the host material confines electron density of the inserted noble gas. Because of this, the interaction of He, Ne, or Ar with O vacancies of ZnO in different charge states (ZnO:VOq) affects the vacancy stability and electronic properties. In particular, we reveal that to minimize the unfavorable overlap of atomic orbitals of the noble gases and surrounding atoms, the noble gases can occupy the vacancy site delocalizing the otherwise localized ZnO:VOq states. |
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T70.00121: Theoretical study on atomic and electronic structures of vacancy-defect complexes in Ga2O3 Kenta Chokawa, Kenji Shiraishi Ga2O3 has been studied as a next generation power semiconductor material which can realize lower energy consumption power devices than those using GaN and SiC.[1] Although some theoretical studies have already clarified the atomic and electronic structures of the point defects such as vacancies,[2] there are few knowledge of the defect complexes in Ga2O3. Therefore, we perform the first principles calculations by using VASP code,[3] and examine the atomic and electronic structures of the vacancy-defect complexes in Ga2O3. We made some vacancy-defect complexes in the α-Ga2O3 and β-Ga2O3 models and determined stable defect structures. We also study the stability of defects in the Mg-doped Ga2O3 models. |
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T70.00122: First-principles prediction of p-type doping of β-Ga2O3 ultrawide bandgap semiconductors Benjamin Tattersfield, Steven Hartman, Guangfu Luo, John Cavin, Rohan Mishra β-Ga2O3 is an ultra-wide-band-gap semiconductor with a large intrinsic band gap of 4.8 eV and a high breakdown field of 8 MV/cm. These properties when combined with the availability of high-quality large-area single crystals of β-Ga2O3, make it attractive for power electronic applications than conventional wide-band-gap semiconductors such as GaN and SiC. However, the efficiency of β-Ga2O3 devices is currently limited by the lack of good p-type dopants. We present evidence based on first-principles density-functional theory calculations that β-Ga2O3 can be efficiently doped p-type by bismuth. Based on formation energies, we predict that bismuth acts as a substitutional dopant at the gallium site. At low concentrations, bismuth leads to delocalized states just above the valence band edge of β-Ga2O3. These states arise due to the antibonding interaction between the occupied 6s2 lone pair electrons of bismuth and the 2p states of oxygen. The occupancy of these delocalized defect states can be controlled by moving the Fermi level, which can lead to efficient p-type doping. |
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T70.00123: Development of Room Temperature Multiferroic SmFeO3 Thin Films Yuan-Chih Wu, Yi-De Liou, Chang-Yang Kuo, Zhiwei Hu, Chun-Fu Chang, Tay-Rong Chang, Heng-Jui Liu, Yi-Chun Chen, Liu-Hao Tjeng, Jan-Chi Yang Multiferroic materials are very popular in recent decades due to its versatile functionalities for applications. A result development of new materials that possesses multiferroicity is of great importance. SmFeO3 (SFO) has been considered as new room temperature single-phase multiferroic material for few years. SFO exhibits anti-ferromagnetism and significant magnetization below TN ∼ 670 K. However, the existence of ferroelectricity of single crystal SFO is still under debate. |
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T70.00124: Epitaxial growth and multiglass order in room-temperature relaxor multiferroics Weichuan Huang, Yen-Lin Huang, Sujit Das, Yun-Long Tang, R Ramesh Multiferroic materials with simultaneous ferroelectricity and magnetism provide a pathway to achieving strong magnetoelectric (ME) coupling with voltage control of magnetism, leading to compact and power efficient electric-field tunable magnetic devices. In recent years, substantial progress in finding room-temperature (RT) relaxor multiferroics, a new perspective for low-power spintronics, displaying strong ME coupling coefficients has been made [1-3]. Here, we present electric and magnetic properties of single-phase xPb(Fe,W)O3-(1-x)Pb(Zr,Ti)O3 (PFW-PZT) films epitaxially grown on (001) SrTiO3 and (220) GdScO3 substrates using pulsed laser deposition. It is demonstrated that the PFW-PZT films show good ferroelectric and piezoelectric properties by measuring macroscopic polarization and local piezoelectric as a function of electric-field. In addition, weak ferromagnetism via magnetic hysteresis loops was also observed at RT. |
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T70.00125: Characterization of TaxTi(1-x)Oy thin film and its applications in RRAM devices. Yu Shi, Rabiul Islam, Guoxing Miao The movement of oxygen ions plays an important role in the resistive switching behavior of TiOx based devices, therefore the designed distribution of oxygen ions may help enhance the oxygen ion's movement and improve the resistive switching performance. In this work, we dope the TiOx thin film with a graded concentration of Ta in depth, to generate a spatial gradient of oxygen activation energy. Detailed characterization of the strcutual changes and resistive switching performance has been carried out, our result may suggest a new way to use dopants to help improve the resistive switching performance. |
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T70.00126: Temperature and field dependent Raman Studies on Cupric Oxide Single Crystals Rajeev Gupta, Barnita Paul Cupric oxide is a well known oxide material which shows two successive magnetic transitions at 230 K (TN2) and 213 K (TN1). Interestingly, it has been reported in recent times that a small electric polarization of 160 μC/m2 develops along the b axis between 213-230 K. The origin of the observed macroscopic polarization is attributed to the noncollinear arrangement of spins and breaking of inversion symmetry via the Dzyaloshinskii-Moriya interaction.This mechanism is rather unusual and was suggested that spin-lattice coupling plays a crucial role. In the current work, we present temperature dependent Raman measurements on single crystalline CuO in presence of a magnetic field. Room temperature Raman measurements reveal three prominent Raman modes at 302 cm-1, 350 cm-1 and 635 cm-1 consistent with earlier reports. Interestingly, we find a new mode appearing at 240 cm-1 below 175 K. This mode splits into two modes on an application of a small magnetic field. Our experiments suggests that the mode observed at 240 cm-1 is a combination of a magnon mode and a zone folded phonon contrary to the earlier reports. |
(Author Not Attending)
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T70.00127: Point defects at ferroelectric domain walls in hexagonal YMnO3 Didrik Småbråten, Sandra Skjaervoe, Dennis Meier, Thomas Tybell, Sverre Selbach Understanding how point defects influence the domain wall (DW) mobility and properties in ferroelectrics is desirable both to control the macroscopic ferroelectric properties and to develop DW-based nanoscale electronic circuitry. Here we use DFT calculations to study the interplay between neutral ferroelectric DWs in improper ferroelectric YMnO3 and lattice imperfections like aliovalent dopant cations and oxygen defects like vacancies and interstitials. We find that the DW mobility and conductivity strongly couples to the defect chemistry of the material, and our simulations are supported by experimental reports. The overall aim of this study is to obtain chemical guidelines from first principles calculations for how to control the DW mobility and conductivity through defect chemistry. YMnO3 displays great chemical flexibility, where donor and acceptor doping of both cation sublattices as well as both oxygen deficiency and excess is possible, making hexagonal manganites an ideal model system for this purpose. |
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T70.00128: Crystal structure and dielectrical behavior of YFe1-xTixO3 Maury Solorzano, Alejandro Duran, Richart Falconi Yttrium ortoferrite, YFeO3, is a multiferroic system despite having a Pnma/Pbnm centrosymmetric structure. The mechanism that gives rise to ferroelectricity is under discussion, but it is believed to be associated with the breakdown of inversion symmetry. In this work, the synthesis, structural characterization, as well as the dielectric properties of the Ti - doped YFeO3 are reported. Structurally it was found that doping with Ti generates an increase in the volume of the unit cell. The relative permittivity, ε'r, increases with the Ti content and has a diffuse phase transition at a temperature that decreases with x. In the same way, both the dielectric loss and the activation energy decrease with Ti doping. These results are discussed considering geometrical aspects and the occupation of the d orbitals. |
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T70.00129: Enhanced charge carrier lifetime in layered 2D hybrid perovskites Polly J Pierone, Noor Titan Putri Hartono, Juan-Pablo Correa-Baena, Tonio Buonassisi, Meng-Ju Sher Lower dimensional layered perovskite exhibited better environmental stability than 3D organic-inorganic hybrid perovskite materials such as methylammonium lead iodide (MAPbI3). Due to the reduced dimensionality, one drawback of these layered 2D perovskite is the reduced charge carrier mobility. Currently, using layered 2D perovskite materials, no improvement in solar cell performance has been reported. In this study, we synthesized layered 2D lead-halide perovskite samples using different ratios of t-butylammonium and methylammonium as the organic cation, creating a set of samples spanning the 3D to 2D transition. We used time resolved terahertz conductivity measurements, a non-contact conductivity probe, to study both charge carrier mobility and lifetime in these materials. We confirmed the reduced charge carrier mobility but found enhanced carrier lifetime, indicating a possibility of finding optimal composition to maximize carrier diffusion length. The increased carrier lifetime supports efficient exciton dissociation and long-lived free carriers recently reported on other 2D Ruddlesden-Popper perovskites. Lastly, we compared the device performance of the 2D perovskite solar cells with the charge carrier dynamics measured. |
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T70.00130: Ultrafast Charge Transfer at CH3NH3PbI3 and MoS2 Interface Wissam Saidi, yongliang Shi, Jin Zhao To achieve higher power conversion efficiency of promising hybrid organic-inorganic perovskites (HOIP), interface engineering must be applied to optimize the charge carrier pathway from absorber to electron and hole transport layers. Fast charge transfer can largely avoid charge accumulation at the interface, and suppress recombination. Further, optimized band alignment between charge transfer material and adsorber would reduce the “potential loss” in the conversion efficiency of the solar cell. Herein, we employ nonadiabatic molecular dynamics (NAMD) within time dependent density functional theory to study hole transfer from CH3NH3PbI3 to monolayer MoS2. Our results show that there is an ultrafast hole transfer channel in agreement with a recent experimental study. Because of the existence of a fast charge transfer and minimal band mismatch between CH3NH3PbI3 and MoS2 at the same time, MoS2 is a promising hole transfer material in HOIP. |
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T70.00131: Epitaxial growth of MoSe2 and MoTe2 monolayer on GaAs by molecular beam epitaxy Yipu Xia, Hailong Wang, Ze Men, JunQiu Zhang, Hao Tian, WingKing Ho, Hu Xu, Jianhua Zhao, MAOHAI XIE Molybdenum diselenide (MoSe2) and molybdenum ditelluride (MoTe2) are promising transition metal dichalcogenides (TMDs) that have attracted great interests in recent years because of their unique electrical and optical properties. In this work, we fabricate crystallographically aligned MoSe2 and MoTe2 monolayers on gallium arsenide (GaAs) (111) surface by MBE as revealed by low energy electron diffraction (LEED) measurements. Unlike TMDs growth on van der Waals (vdW) substrates such as the highly oriented pyrolytic graphite (HOPG) and graphene, the interface interactions between GaAs and the epitaxial TMD films are electronically stabilized surface as suggested by X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Ultraviolet photoelectron spectroscopy (UPS) measurements are also performed to provide additional evidence and results. |
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T70.00132: Transport and photoresponse study of Bulk MoS2 Mehdi Pakmehr, Mojtaba Ebrahimi, Hajar Kazemi, Zohreh Mohammadi Molybdenum disulfide (MoS2) or Molybdenite were known as an indirect gap semiconductor with energy gap of 1.8 eV. More recently, it turns out that in 2D morphology (atomic thin film case) MoS2 hosts novel physical properties including high optical absorption coefficient. To be used as a common semiconductor material within electronic and optoelectronics industry, one needs to know the types of impurity atoms within by-product powder of MoS2 from copper extraction factory. We investigated structural properties of powder MoS2 through PXRD, which confirm MoS2 with reasonable purity. The powder used for bulk polycrystalline sample growth through common melting techniques. Transport measurements at cryogenic temperatures done to check conductivity of our bulk sample. Due to unintended dopant species, we observed conductivity dependence on temperature in range of 80-300 K. We plan to present our finding through a poster at APS march meeting 2019 being held at Boston. |
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T70.00133: Thermal and Electrical Transport Properties in bulk Ge2Sb2Te5 Ming Yin, Jereshia Bush, Lei Wang, Timir Datta The remarkable ability of certain solids, the Phase Change materials (PCM), to reversibly and rapidly switch between amorphous and crystalline states with large differences in electrical, thermal and optical properties was discovered exactly half a century ago [S.R. Ovshinsky PRL, 21,1450 (1968)]. Currently ambient temperature operable PCM’s are used in electronic flash memory as well as optical data storage. Ge2Sb2Te5 is such a PCM alloy; in which, we have previously reported Noritheim-Gorter like scaling between Seebeck coefficient (S) and electrical conductivity (s). Here we report that in the room temperature regime, thermal conductivity (κ) of this material is a linear function of temperature with a slope ~ 1e-3 W/mT2; whereas, electrical conductivity falls off with rising temperature; Remarkably, despite this deviation from Wiedemann-Franz Law, the value of Lorenz number estimated from the experimental (κ and s) data ranges between 2-2.47 e-8 WWK-2, not much off from the ideal kinetic theory value of 2.44e-8. Further experimental details and results will be discussed. |
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T70.00134: Photoexcited dynamics in tellurium probed by coherent phonons Yu-Hsiang Cheng, Samuel W Teitelbaum, Frank Gao, Keith Adam Nelson We studied the photoexcited dynamics in tellurium films using ultrafast pump-probe spectroscopy. Photoexcitation with femtosecond laser pulses produces carriers that modify the interatomic potential and thus excite coherent phonons. The phonon frequency strongly depends on the carrier density and the lattice temperature. We estimated the carrier density and the corresponding electronic bond softening using the diffusion equation. We also measured the phonon dynamics at different temperatures from 80 to 500 K. Based on these measurements, the lattice temperature within 1 ns after the pump pulse can be estimated using the frequency of the coherent phonons, excited by a second pump pulse. In addition, we modified the two-temperature model to simulate the dynamics of the carrier density, carrier temperature, lattice temperature, and phonon motion at different depths. |
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T70.00135: On the pitfalls of applying isotropic mobility spectrum analysis to conductors with weak anisotropy Kenneth S. Stephenson, Yaroslaw Bazaliy It is shown that applying isotropic quantitative mobility analysis (QMSA) to anisotropic materials can lead to drastic qualitative errors, even in the case of modest anisotropy. The procedure may provide not only wrong values for carrier mobilities and concentrations, but even a wrong number of carrier species. |
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T70.00136: Multiscale study on Phase Transformation of Ceramic Materials Yuhuan Fei Compared with their microstructures, phase analysis of ceramic materials is rarely reported. Generally, phase analysis includes experimental phase structure determination and theoretical simulation, which are quite challengeable and require a heavy workload. Here, we proposed a series of simulation methods to analyze the phase transformation during the sintering process of Al2O3-ceramic materials. The structures of generated Al-Mg phases were simulated using XPFC method. The obtained potential function of Ti-C-N was applied to simulate the formation of generated Ti-C-N phases with MD methods employed. Combined with corresponding experimental results, the relationship between specific phases and mechanical properties were established. |
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T70.00137: In situ investigation of electric field and stress control of ferroelectric phases in PIN-PMN-PT single crystal Peter Finkel, Margo Staruch, Markys Cain We explored stability of relaxor ferroelectric single crystals with composition near a morphotropic phase boundary (MPB) using the three-pronged approach offered by this project of in situ, stress, temperature and E field whereby a bias of any one of these parameters can move the operating point in almost any direction.This MPB can be moved through the application of stress or electric field. In this work we demonstrate an induced rhombohedral (R) to orthorhombic (O) phase transition in [011] cut Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3(PIN-PMN-PT) single crystal relaxor ferroelectric, that can be simultaneously tuned through combination of stress and applied electric field. Direct observations of this phase transition with X-ray and Raman scattering reveal the local symmetry while sweeping through the transition with a low applied electric field when the crystal is near a critical value of stress. A coexistence of R and O phases was observed and these microscopic measurements mirror the bulk strain in the sample. Remarkably, cycling through this transition can generate reversible strain >0.35% for tens of millions of cycles with little fatigue. Details of these results and their implications will be presented. |
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T70.00138: Ab initio studies of electronic and vibrational properties of transition metal dichalcogenides systems under hydrostatic pressure Tomasz Wozniak, Jan Kopaczek, Robert Oliva, Pawel Scharoch, Jordi Ibanez, Robert Kudrawiec We study from first principles (DFT) the electronic structure of MoTe2 and WS2 under hydrostatic pressure in comparison to photoreflectance spectra. The analysis based on pressure coefficients allowed for identification of several optical transitions in bulk and multilayer systems. The calculated pressure coefficients for K and H point transitions are in good agreement with the experimental values. [1] |
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T70.00139: Synthesis and Optical Properties of Fluorine-Doped Zinc Tin Oxide Thin Films Prepared by Ultrasonic Spray Pyrolysis Ahmed Hegazy, Belal Salameh, Abdel Khalq M Alsmadi Thin films of fluorine-doped zinc tin oxide (FZTO) were prepared by ultrasonic spray pyrolysis (USP) at various concentrations of Zn and F. The defect levels in the bandgap were determined by the photoluminescence (PL) measurements. Optical transitions between defect and band levels were identified by the analysis of the absorption spectra. The ascription of defect levels to oxygen vacancies was supported by the measurements of x-ray photoelectron spectroscopy (XPS). |
(Author Not Attending)
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T70.00140: Modeling and Simulation of GaTlAs Quantum Well Solar Cells Ahmed Zayan, Thomas Vandervelde Multiple Quantum Wells (MQW) have been an ongoing topic of research and discussion for the scientific community with structures like InGaAs/GaAs and InGaP/GaAs quantum wells producing promising results that could potentially improve overall solar energy conversion. Here, we use WEIN2K, a commercial density functional theory package, to study the ternary compound Ga1-xTlxAs and determine its electronic properties. Using these results combined with experimental confirmation we extend these properties to simulate a MQW GaAs/ Ga1-xTlxAs solar cell. Ga1-xTlxAs is a tunable compound, with its bandgap being strongly dependent on the concentration of Tl present. Concentrations of Tl as low as 7% can reduce the bandgap of Ga1-xTlxAs to roughly 1.30 eV at room temperature with as little as a 1.7% increase in lattice constant. The change in bandgap, accompanied by the relatively small change in lattice constant makes Ga1-xTlxAs a strong candidate for a MQW cell with little to no strain balancing required within the structure to minimize unwanted defects that impede charge collection within the device. Our GaAs photodiode with TlGaAs MQWs shows an expanded absorption band and improved conversion efficiency over the standard GaAs photovoltaic cell. |
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T70.00141: WITHDRAWN ABSTRACT
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T70.00142: Charge carrier lifetime dependence on annealing conditions in copper oxide thin films: A transient absorption study
Learnmore Shenje, Dr Suzanne Ullrich Lenny Shenje Ultrafast transient absorption spectroscopy has been used to study charge carrier dynamics in Copper(I) and Copper(II) oxide thin films as a function of annealing conditions. 16 samples were deposited on glass substrates and then subsequently annealed at temperatures 150 to 380 C for periods ranging from 2 to 24 hrs. Clear evidence of oxidation from the copper (I) to the copper (II) phases was observed by steady state and time-resolved spectroscopies as well as x-ray diffraction. Thin film transient absorption spectra were recorded by exciting the samples across the band gap and probing subsequent carrier dynamics with a white light continuum. The mixed Cu2O/CuO thin film transient spectra were compared to those of pure Cu2O and CuO to investigate the influence of annealing conditions on the films’ optical properties. All samples showed multi-exponential decay kinetics with a fast component (ranging from 0.2 – 0.5 ps) and a long-lived component (>1 ns); an additional 0.8 to 3 ps intermediate time constant was observed in mixed Cu2O/CuO and pure CuO films. These kinetics are attributed to carrier relaxation in the conduction band, trapping and recombination. |
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T70.00143: WITHDRAWN ABSTRACT
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T70.00144: Two-dimensional Fourier Transform Spectroscopy on Bulk GaAs in High Magnetic Fields Christopher E Stevens, Varun Mapara, Jagannath Paul, Myron Kapetanakis, Stephen A McGill, Ilias Perakis, Denis Karaiskaj Two-dimensional Fourier transform spectroscopy was performed on Bulk GaAs in the presence of magnetic fields up to 10T. The polarization dependent exciton dynamics were studied in addition to the effects of an applied external magnetic field. The experimental results were then modeled using the optical Bloch equations. |
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T70.00145: Quantum beats of a multiexciton state in crystalline rubrene Drew Finton, Eric Wolf, Vincent Zoutenbier, Ivan Biaggio We have observed quantum beats in the photoluminescence dynamics of the organic molecular crystal rubrene following photoexcitation by a femtosecond pulsed laser. The application of a magnetic field up to 0.3 T, created by a neodymium permanent magnet, produces periodic modulations in the photoluminescence dynamics. The beat frequency ranges between 0.6 GHz to 1.3 GHz and is dependent upon the relative orientation of the magnetic field and the crystalline axes. The amplitude of the beats increases with increasing magnetic field strength, peaking at about 5% of the non-oscillatory background. These beats are indicative of a multiexciton state consisting of a spin-coherent pair of triplet excitons existing during the singlet-to-triplet exciton fission conversion process. |
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T70.00146: ABSTRACT WITHDRAWN
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T70.00147: Electrical Characterization of Semiconductor Nanostructure Based Capacitors Masoud Kaveh-Baghbadorani, W Christopher Hughes, Maeven Luedke, Nikolas Roeske, Josh Mitri, Fazel Baniasadi, Chenggang Tao, Hoe Tan, Mykhaylo Lysevych, Chennupati Jagadish Semiconductor nanostructures are employed as dielectric materials to investigate the performance of a capacitor. We study the effect of geometry and the type and thickness of semiconductors on the total capacitance using electrical measurements. SrTiO3 nano-powder and GaAs and Si nanowires (NW) are chosen for their relatively high dielectric constant. For capacitor plates we deposit ~30 nm Au on both solid glass and flexible PMMA substrate using an electron beam deposition system. The vertically aligned 50 nm diameter GaAs NWs were grown using the Au catalyzed vapor-liquid-solid method. The Si NWs are randomly oriented with an average diameter of 70 nm. The SrTiO3 nano-particles are cubical with a width of around 30 nm. Parallel arrays of GaAs NWs, as well as a random distribution of Si NWs or SrTiO3 nano-powder, lying between two Au coated substrate is composing the capacitors. Capacitance measurements on the reference sample, Au plates with air dielectric spacer, reveal capacitance in the pico-Farad order at room temperature. Capacitor structures with semiconductor dielectrics however show an enhancement of the total capacitance, mainly explained by the semiconductor spacer weakening the effective internal electric. |
(Author Not Attending)
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T70.00148: A Ferroelectric Semiconductor Field-Effect Transistor Mengwei Si, Gang Qiu, Peide (Peter) Ye A ferroelectric semiconductor field-effect transistor (FeS-FET) was proposed and experimentally demonstrated for the first time. In this novel FeS-FET, a 2D ferroelectric semiconductor α-In2Se3 is used to replace conventional semiconductor as channel. α-In2Se3 is identified due to its proper bandgap, room temperature ferroelectricity, the ability to maintain ferroelectricity down to a few atomic layers and the feasibility for large-area growth. An atomic layer deposited (ALD) Al2O3 passivation method was developed to protect and enhance the performance of the α-In2Se3 FeS-FETs. The fabricated FeS-FETs exhibit high performance with a large memory window, a high on/off ratio over 108, a maximum on-current of 671 μA/μm, high electron field-effect mobility with μFE= 312 cm2/Vs in forward sweep and μFE= 488 cm2/Vs in reverse sweep, and the potential to exceed the existing Fe-FETs for non-volatile memory applications. |
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T70.00149: Minimal double quantum dot in ZnO Junyi Zhang, Hao Zheng, Richard Berndt Minimal double quantum dots (DQDs) are prepared in ZnO, a wide band-gap semiconductor matrix. The QDQs are of the atomic scale that is difficult to achieve for for conventional microfabrication techniques. It is comprised of a pair of strongly coupled donor atoms that can each be doubly charged. Using scanning tunneling microscopy and spectroscopy, we mapped out the donor excitation diagram of this system which mimicks the charge stability diagram observed in transport measurements of DQDs. The charge and spin degrees of freedom of the minimal DQDs may also be used as quantum bits. The DQDs can be prepared in the quantum entangled state, e.g., in a Bell state. The results open an intriguing perspective for quantum electronics with atomic-scale structures. |
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T70.00150: Resistance drift of metastable amorphous and crystalline fcc GeSbTe memory devices Helena Silva, Nafisa Noor, Shalini Tripathi, C. Barry Carter Phase-change memory is an emerging technology that utilizes the electrical resistivity contrast between the amorphous and crystalline phases of chalcogenide glasses to store data. The most commonly used material for PCM has been GeSbTe (GST), which has metastable amorphous and crystalline fcc phases and a stable crystalline hcp phase [1]. One difficulty with the implementation of PCM is the upward resistance drift of the metastable amorphous and crystalline fcc phases. We are using electrical characterization together with transmission electron microscopy and finite-element electrothermal simulations [2] to study the physical mechanisms that give rise to the electrical resistance drift of GST cells. |
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T70.00151: SUPERCONDUCTIVITY
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T70.00152: Iron based superconductors on flexible coated conductor templates Aleena Thomas, Kornelius Nielsch, Dr.Ruben Hühne The discovery of high temperature superconductivity in layered iron-based material has ignited also significant scientific interest for technological applications. Iron based superconductors are particularly promising for high field applications due to its high upper critical field and low anisotropy. To realize such applications, the coated conductor technology based on textured IBAD (Ion beam assisted deposition) layers can be used. Additionally, such templates might be applied to investigate the influence of uniaxial strain on the superconducting properties. Therefore, we deposited pure as well as Te doped FeSe with a thickness of up to 200 nm on buffered IBAD substrates having a final cap layer of either CeO2 or LaMnO3. We found that FeSe1-xTex (FST) and FeSe is grown epitaxially on these buffered metal tapes under optimized conditions with a superconducting transition temperature of up to 16 K for textured FST film on CeO2 buffered metal tape. Finally, we will present first results on the influence of uniaxial strain on the superconducting transition using these templates. |
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T70.00153: Measurements of Superconducting Anisotropy in FeSe with Resonance Frequency Technique Rongxing Cao, Jun Dong, D. A. Chareev, A. N. Vasiliev, Guoqing Wu, Xianghua Zeng Utilizing a novel method with the resonance frequency of a LC circuit, we measured the superconducting anisotropy of single crystals of Fe-based superconductor FeSe. We found that the temperature dependence of the upper critical field Hc2(T ) of FeSe coincides with the Werthamer-Helfand-Hohenberg (WHH) model when taking the Maki parameter α into consideration, which suggests an important role played by spin-paramagnetic effect in suppressing the superconductivity. When temperature T → 0, the values of Hc2,||c(0) and Hc2,||ab(0) derived from the WHH fitting are close to and within the range of the Pauli limit, for field H0 applied parallel to the c-axis and to the ab-plane, respectively. As compared with other typical iron-based high-Tc superconductors, lower values of Hc2(0) and higher superconducting anisotropy were found in FeSe. |
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T70.00154: Phases and Phase Transitions of an Anisotropic Ising-O(3) Model Anzumaan Chakraborty, Thomas Vojta The two-dimensional anisotropic Ising-O(3) model is an effective Hamiltonian for the |
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T70.00155: Magnetic properties of bulk and monolayer FeSe : A DFT+DMFT study Chang-Youn Moon FeSe is unique among other iron-based superconductors, which shows no magnetic ordered state and becomes superconducting below 8 K in the undoped bulk system while the superconducting transition temperature soars by an order of magnitude for a monolayer FeSe on SrTiO3 substrate. Using a DFT+DMFT method, we perform a comparative study on the magnetic properties of FeSe systems and LaFeAsO, another representative iron-based superconducting material. Calculated magnetic moment in the typical stripe-type magnetic ordering pattern is finite for LaFeAsO while negligible for bulk FeSe, consistently with experiments, and is also finite for monolayer FeSe suggesting the magnetic order is restored in monolayer FeSe. We suggest a mechanism explaining why the systems with the similar magnitudes of fluctuating spin (<S2>) have very different magnitude of ordered moment (<Sz>) focusing on the different aspects of local charge fluctuation. Our work provides a comprehensive understanding of magnetism in iron-based superconducting materials, and also emphasizes on the potential importance of magnetism in the high superconducting transition temperature of monolayer FeSe on SrTiO3 substrate. |
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T70.00156: The nematicity induced d-symmetry charge density wave in electron-doped iron-pnictide superconductors Hong-Yi Chen The interplay among the nematicity, the stripe spin-density-wave (SDW) order and superconductivity in iron-pnictides is studied in a self-consistent Bogoliubov-de Gennes equations. Our calculations have shown that the nematic-order breaks the degeneracy of dxz and dyz orbitals and causes the elliptic Fermi surface near the Γ point in the normal state. In addition, the appearance of the orthorhombic magnetic fluctuations generates two uneven pairs of peaks at (±π,0) and (0,±π) in its Fourier transformation. All these are comparing favorably with experimental measurements. In the nematic phase, our results indicate that the charge density and its spatial image in the local density of states exhibit a dx2-y2-like symmetry. Finally, the complete phase diagram is obtained and the nematic phase is found to be in a narrow region close to the SDW transition in the electron-doped iron-pnictide superconductors. |
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T70.00157: Point Contact Spectroscopy of Iron Pnictides: Probing Superconductors to Observe the Gap Structures of (P, Co, K) Doped Iron Pnictides Brett Conti, Oberon O Wackwitz, Keeran Ramanathan, Gabrielle Moss, Chenglin Zhang, Yu Song, Guotai Tan, Pengcheng Dai, Roberto Ramos We used a four-wire point contact spectroscopy system to obtain differential conductance (dI/dV) measurements in order to observe the energy gap structures of phosphorus, cobalt, and potasium doped iron-pnictides with varying doping levels at 2K. We were motivated to study the iron pnictides because they were only recently discovered to be superconducting (~2007) due to the presence of iron which is traditionally expected to quench all superconducting properties, and also because the iron pnictides can exhibit multi-gap structures like those of magnesium di-boride. Our goal was to obtain the differential conductance measurements for varying x values of phosphorus,cobalt, and potassium, and observe the gap structures of the various families to further characterize and understand the superconducting transition of these iron pnictides. We observed both single and double gap structures for various x values, with delta 1 ~ 2-5 meV, and delta 2 ~ 7-10 meV. We will report additional results from this ongoing work. |
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T70.00158: Growth of ultra-thin high-Tc FeSe0.5Te0.5 film with high Tc on piezoelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates by pulsed laser deposition Lin Zhu, Yonggang Zhao The influence of strain on the electrical transport properties of iron chalcogenide superconductors FeSexTe1-x may offer insight into the mechanism of superconductivity. The inverse piezoelectric effect from a piezoelectric substrate provides a method of continuous tuning of the lattice deformation on one and the same sample. Single-crystalline piezoelectric Pb(Mg1/3Nb2/3)Ti0.3O3 (PMN-PT) substrates have been shown to allow reversible and dynamic control of biaxial strain in epitaxially grown thin functional films. Here we present an effective method to significantly improve the epitaxy of superconducting FeSe1-xTex thin films via the introduction of a semiconducting buffer layer of FeSe1-xTex. The buffer layer enables subsequent growth of superconducting FeSe1-xTex at reduced deposition temperatures (275°C) on PMN-PT by pulsed laser deposition. The films exhibit consistently high critical temperatures (≥16 K); the FeSe1-xTex thin films show Tc as high as 15 K even when the thicknesses are less than 10 nm. This work demonstrate a versatile platform to investigate the relationship between structure and superconductivity in FeSexTe1-x thin films. |
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T70.00159: Direct Visualization of the Nematic Superconductivity in CuxBi2Se3 Ran Tao CuxBi2Se3 hosts both topological surface states and bulk superconductivity. It has been identified recently as a topological superconductor (TSC) with an extraordinary nematic, i. e. C2-symmetric, superconducting state and odd-parity pairing. Here, using scanning tunneling microscopy (STM), we directly examine the response of the superconductivity of CuxBi2Se3 to magnetic field. Under out-of-plane fields (B⊥), we discover elongated magnetic vortices hosting zero-bias conductance peaks consistent with the Majorana bound states expected in a TSC. Under in-plane fields (B//), the average superconducting gap exhibits two-fold symmetry with field orientation; the long C2 symmetry axes are pinned to the dihedral mirror planes under B//=0.5 T but rotate slightly under B//=1.0 T. Moreover, a nodeless Δ4x gap structure is semi-quantitatively determined for the first time. Our data paint a microscopic picture of the nematic superconductivity in CuxBi2Se3 and pose strong constraints on theory. |
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T70.00160: SUPERCONDUCTING TRANSITION TEMPERATURE OF A BORON NITRIDE LAYER WITH A HIGH TITANIUM COVERAGE. Fernando Magana, Gerardo J Vazquez We explore the possibility of inducing superconductivity in a Boron Nitride (BN) sheet, by doping its surface with Ti atoms sit on the center of the BN hexagons. Defining the coverage M as the ratio of the number of atoms of titanium to the number of hexagons of BN per cell, we take the cases of M = 1 and 1/3. We used first-principles density functional theory in the general gradient approximation. The Quantum-Espresso package [1] was used with norm conserving pseudopotentials. The structure considered was relaxed to their minimum energy configuration. Phonon frequencies were calculated using the linear-response technique on several phonons wave-vector mesh. The electron-phonon coupling parameter was calculated with several electron momentum k-mesh. The superconducting critical temperature was estimated using the Allen-Dynes formula with μ* = 0.1 - 0.15. We note that Ti is a good candidate material to show a superconductor transition for the BN-metal system. |
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T70.00161: Superconductivity in Niobium Nitride Tsu-Lien Hung, Min-Nan Ou, Fan-Yun Chiu, Ting-Kuo Lee, Yang-Yuan Chen Niobium nitride is a well-known superconductor with many excellent physical properties, such as high hardness, high shear rigidity, high bulk modulus. It has several structure phases, including cubic, hexagonal, and tetragonal. Among these phases, the cubic phase has been extensively studied the superconductivity with a wide range of Tc, 9 ~ 17 K. In our work, the cubic phase specimens of NbN were been measured by X-ray diffraction, magnetic susceptibility, resistivity, and specific heat. We observed that the Tc of cubic phase appeared 13.6 K from magnetic and specific heat measurements. Very recently the hexagonal phase of epsilon-NbN (ε-NbN) has been reported to have the superconducting transition temperature about 11 K [1]. A micron sized NbN crystal was obtained from commercial product, and confirmed to be epsilon phase by electron back-scattering diffraction (EBSD) technique. However, no superconductivity was found in the micron sized epsilon-NbN crystal. We inferred that the superconductivity of epsilon-NbN reported in literature may have shorter Nb-N bond length as that of the cubic NbN phase which is about 0.02 Å shorter than our epsilon-NbN crystal. |
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T70.00162: ABSTRACT WITHDRAWN
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T70.00163: Crystalchemistry and Thermodynamics in ZnMgO2, Zn2MgO3 and Zn3MgO4 compositions. Daniel Iván Guillén Carrillo, Elizabeth Chavira, Ricardo Ernesto Paniagua, Jose Antonio Hurtado, Karla Eriseth Morales, Adriana Tejeda, Jesús Ángel Arenas, Jorge Barreto, Roberto Ysacc Sato In 2016 was reported the ZnMgO2 115 K, Zn2MgO3 132 K y Zn3MgO4 152 K superconductors. Our interest was study the thermodynamic behaviour, which did not reported jet. Of course, also study their crystal structure and magnetic properties. Searching in the phase diagrams thermodynamic equilibrium, we found the binary Zn0-MgO system. Then the SC compositions were in the region of the mixture of zincite-periclase solid solutions. |
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T70.00164: SYNTHESIS OF (Bi1.7Pb0.3)Sr2Ca2Cu2O10 NANOMATERIAL SUPERCONDUCTOR. Ricardo Ernesto Paniagua Martinez, Elizabeth Chavira, Daniel Ivan Guillen Carrillo, Rodolfo Ivan Cruz Hernandez, Adriana Tejeda, Karla Eriseth Morales, Jesús Ángel Arenas, Jorge Barreto The purpose of the study of the synthesis of the compound (Bi1.7Pb0.3)2Sr2Ca2Cu2O10 is to characterize the properties of the superconductivity in the (Bi1.7Pb0.3)2Sr2Ca2Cu2O10 when it is found as a nanocrystal in the stabilized 110 K superconducting compound, which will be induced in a single superconducting compound with the addition of lead that will substitute in the proportion of 15% of a bismuth, the final product will be characterized by XRD and SQUID. |
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T70.00165: Pairing in quantum-critical systems: Tc, Δ and their ratio Yi-Ming Wu, Artem G Abanov, Andrey Chubukov We calcualte the ratio of the pairing gap Δ at T=0 and Tc for a set of quantum-critical models in which the pairing interaction is mediated by a gapless boson(the γ model, where different γ corresponds to different pairing models). The ratio 2Δ/Tc has been recently computed numerically for 0<γ<2 within Eliashberg theory and was found to increase with increasing γ [T-H Lee et al, arXiv:1805.10280]. We argue that the origin of the increase is the divergence of this ratio at γ = 3. We obtain an approximate analytical formula for the ratio for γ<3 and show that it fits numerical data well. We also consider in detail the opposite limit of small γ. Here we obtain the explicit expressions for Tc and Δ, including numerical prefactors. We show that these prefactors depend on fermionic self-energy in a rather non-trivial way. The dependence is, however, the same for Tc and Δ, and the ratio 2Δ/Tc approaches the BCS value 3.53 when γ approaches to 0. |
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T70.00166: Thermodynamic Properties of a nano-gram NbN crystal by 3ω Method Fan-Yun Chiu, Min-Nan Ou, Chia-Seng Chang, Yang-Yuan Chen Niobium nitride is a well-known superconductor, which has several structure phases, including cubic, hexagonal, and tetragonal. Among them, the cubic phase has been extensively studied, and shows a superconductivity transition temperature (TC) in a wide range of TC =9 ~ 17 K. In order to study the superconductivity of a single crystalline NbN, a NbN crystal with um size was selected from a commercial powder. The phase of selected crystals were confirmed by powder x-ray diffraction and electron backscatter diffraction (EBSD) analysis. In this work, crystals placed on a nanowire-device (ND) for studying its thermodynamic properties by 3ω method. The fabricated ND (30 μm × 600 nm × 100 nm) was carried out by means of thermal and sputtering deposition, and optical and e-beam lithography on a Si3N4/Si wafer. The chemical etching techniques followed up to realize the sagging of the ND from the membrane for thermal isolation. By 3w technique, the temperature dependent specific heat and thermal conductivity of a NbN crystal at low temperatures were investigated. The details will be discussed in the presentation. |
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T70.00167: Structural and electronic behaviors of YBa2(Fe1-xMnx)3O8+δ Richart Falconi, Maury Solorzano In this work, the synthesis, structural, electrical and magnetic characterization of the set of polycrystalline samples: YBa2(Fe1-xMnx)3O8+δ, with |
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T70.00168: Apical dynamics modulated in-plane properties in cuprates. Sooran Kim, Xi Chen, William Fitzhugh, Xin Li Since the discovery of high-temperature superconductivity in hole-doped La2CuO4, the mechanism of cuprate superconductors has been one of the most important problems in condensed matter physics. In this talk, we show, using ab initio simulations, a new trend that the bonding strength between the apical cation (e.g. La, Hg, Bi Tl) and apical anion (O, Cl) is positively correlated with experimental Tc,max across the hole-doped cuprates. The “apical structure unit” formed by the apical anion and the apical cation, the in-plane Cu and its nearest oxygen neighbors is a fundamental building block that can couple dynamically to control the superconductive properties. We present the underlying fundamental phenomena of coupled apical charge flux and the phonon/lattice dynamics of apical oxygen. Cooperative apical charge fluxes modulate the in-plane transport property by dynamically change both hopping integral and charge transfer energy. We believe our understanding here can shed light on the understanding of the complicated phenomena in cuprates, especially how the transport properties are controlled by the coupled electronic and ionic dynamic oscillations. |
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T70.00169: Atomically-resolved charge modulation of YBa2Cu3O7-x using cross-sectional scanning tunneling microscopy Chun-Chih Hsu, Bo-Chao Huang, Chia-Seng Chang, Ya-Ping Chiu Short-range charge density wave (CDW) order is found universally among underdoped high-Tc superconductors. However, a picture on how CDW order propagates through CuO2 planes remains ambiguous. In this work, we presented cross-sectional scanning tunneling microscopy and spectroscopy measurement on YBa2Cu3O6.81 thin film and probed both atomic and electronic structure simultaneously along the c-axis. Our real-space observation reveals the existence of the charge modulation on CuO2 plane and CuO chain layers. The periodicity of charge modulation exhibits a wide distribution with peak value λ ≈ 1.3 nm and is correlated across layers, implying a close connection of CuO2 plane and CuO chain layer. |
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T70.00170: Thre-Dimensional Fermi Surface of Overdoped La-based Cuprates Kevin Hauer, Masafumi Horio, Yasmine Sassa, Zarina Mingazheva, Denys Sutter, Kevin Kramer, Ashley Cook, Elisabetta Noceroni, Ola Kenji Forslund, Martin Månsson, Oscar Tjernberg, Masaki Kobayashi, Alla Chikina, Thorsten Schmitt, Vladimir Strocov, Sunseng Pyon, Takagi Takayama, Hidenori Takagi, O.J. Lipscombe, Stephen Hayden, Titus Neupert, Christian Matt, Johan Chang On this poster, we present a soft x-ray angle-resolved photoemission spectroscpoy study of the high-temperature superconductors La2-xSrxCuO4 (LSCO) and La1.8-xEu0.2SrxCuO4.Mapping in-plane and out-of-plane components of the Fermi surface reveals a distinct kz-dispersion, that was parametrizing a tight binding model [1]. In this fashion, we quantify the contribution of the van Hove singularity to specific heat found in over doped LSCO can't be assigned to the van Hove singularity and is theefore taken as evidence of quantum criticality. |
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T70.00171: Vortex dynamics and hysteretic flux losses due to pinning Danilo Liarte, Daniel Hall, Peter N. Koufalis, Akira Miyazaki, Alen Senanian, Matthias Ulf Liepe, James Patarasp Sethna We use a model of vortex dynamics and collective weak pinning theory to study the residual dissipation due to trapped magnetic flux in a dirty superconductor. Using simple estimates, approximate analytical calculations, and numerical simulations, we make predictions and comparisons with experiments performed in CERN and Cornell on resonant superconducting radio-frequency NbCu, doped-Nb and Nb3Sn cavities. We invoke hysteretic losses originating in a rugged pinning potential landscape to explain the linear behavior of the sensitivity of the residual resistance to trapped magnetic flux as a function of the amplitude of the radio-frequency field. Our calculations also predict and describe the crossover from hysteretic-dominated to viscous-dominated regimes of dissipation. We propose simple formulas describing power losses and crossover behavior, which can be used to guide the tuning of material parameters to optimize cavity performance. |
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T70.00172: Vortex dynamics in temperature gradients: Magnetic flux expulsion in type-II superconductors. Alen Senanian, Danilo Liarte, James Patarasp Sethna How do vortices in type-II superconductors get expelled as they are cooled down to the Meissner state? Experiments at Fermilab and Cornell on superconducting radio-frequency cavities suggest thermal gradients are the main mechanism behind flux expulsion. Trapped flux significantly contributes to power losses in particle accelerators, thus understanding expulsion is vital to optimizing cavity performance. Here we re-derive the thermal gradient force acting on vortices and study vortex dynamics when this force is offset with pinning forces and vortex-vortex interactions. We show that a thermal gradient acting on interacting vortices is sufficient for flux expulsion in the absence of impurities. We then introduce collective weak pinning and use recent results to obtain analytic expressions for the balance of these forces for isolated vortices. We further explore flux trapping mechanisms by modeling pinning of vortices on strong, but local, pinning centers. By including vortex-vortex interactions in addition to vortex-impurity interactions, we numerically explore their implications on trapped magnetic flux. Finally, we consider the consequences of dendritic inhomogeneity in the cooling temperature-front on flux trapping. |
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T70.00173: Josephson Junctions Containing Antiferromagnetic FeMn and IrMn for Cryogenic Memory Application Robert Michael Klaes, Bethany M Niedzielski, Thomas Joseph Bertus, Reza Loloee, Norman Owen Birge The study of ferromagnetic Josephson junctions for cryogenic memory applications is an area of intense research interest. The prototypical memory device takes the form of an S/F/F’/S spin valve where the two ferromagnetic layers [F, F’] have different switching fields. Switching the relative magnetizations of the two layers between parallel and antiparallel tunes the ground state phase difference across the junction to either 0 or π [1], and corresponds to a bit in a proposed memory cell [2]. It is necessary to design a device where the magnetization of the hard F’ layer is robust within the switching field range of the soft F layer. A traditional method of accomplishing this in MRAM applications is to exchange-bias one of the layers by pinning its magnetization with an adjacent antiferromagnetic layer. To determine if that method can be used in cryogenic memory, we have fabricated Josephson junctions containing FeMn/NiFe and IrMn/NiFe bilayers. We present the results in this poster. |
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T70.00174: Terahertz Emission From Annular Microstrip Antennas Amanda Vasquez, Sheila Bonnough, Richard Klemm One of the most promising proposed sources of terahertz (THz) electromagnetic radiation is superconductor-based devices. These superconductors work by utilizing the intrinsic Josephson junctions (IJJs) present in single crystals of the superconductor Bi2Sr2CaCu2O8+δ (BSCCO). To exploit the Josephson effect, a groove is inscribed in a crystal of BSCCO, producing a mesa about 1 μm thick of any shape, the geometry of which determines the emission spectrum. Alternatively, much more efficient stand alone mesa structures can be built in the desired geometry. The mesa or mesa cavity effectively functions as a microstrip antenna, which can be analyzed using standard antenna theory. |
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T70.00175: Characterization of cavity mode and radiation pattern in superconducting coherent terahertz emitters Kaveh Delfanazari, Richard Klemm, Manabu Tsujimoto, Daniel Cerkoney, Takashi Yamamoto, Takanari Kashiwagi, Kazuo Kadowaki We discuss the broadly tunable terahertz (THz) radiation in solid state terahertz (THz) emitters based on high-temperature superconducting Bi2Sr2CaCu2O8+δ (Bi-2212). We experimentally measure the current-voltage characteristics (IVC) of mesas of different geometries, such as triangular-, pentagonal-, hexagonal-, and elliptical- cavities, and compare the IVC of the radiating and no-radiating cavities. The THz emission spectra in radiating THz cavities was measured using the Fourier transform infrared spectrometer in order to elucidate the radiation mechanism of the emitters. Moreover, we experimentally and theoretically study the angular dependence of the emission intensity obtained in mesas’ plane at various frequencies and detection angles, by rotating the sample holder relative to the detector, to identify the excited EM cavity modes within the cavities that participate in the emitter output power enhancement. |
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T70.00176: Towards Measuring Vacuum Polarization of Quantum Electrodynamics with Superconducting Junctions Ali Rad In this proposal, we present an experimental setup based on superconducting circuits and Joseph- son junctions to explore the modification of Josephson coefficient in the presence of external magnetic field due to vacuum polarization of quantum electrodynamics. This robust experiment can be con- sidered as one of the few possible chances to observe the fine quantum field theory corrections in the low energy regimes in condensed matter systems. It can also be a new check for the universality of Josephson constant which is important in metrology. We will expect the signal to noise ratio of the read-out signal to increases quadratically by running time of the experiment. This characteristic of the output signal the will guarantee the feasibility of measurements with desired precision |
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T70.00177: Device for extraction of Majorana current by means of Fraunhofer diffraction in proximitized superconducting arrays Xiangyu Song, Yang Bai, James Eckstein, Alexey Bezryadin We propose a geometry in which the supercurrent carried by Majorana zero modes dominates the ordinary supercurrent. The devices is tunable through the Fraunhofer diffraction. The contribution of the Majorana current is further amplified by organizing an array of conducting channels. This system can act as a tunable source of Majorana current. |
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T70.00178: Ferromagnetic Resonance Properties of NbCrFeCrNb multilayer stacks Murat Cubukcu, Sachio Komori, Alexander Vanstone, Juliet Johnson, Alexander Chan, Kun-Rok Jeon, Mark Blamire, Jason Robinson, Lesley Cohen, HIdekazu Kurebayashi It is by now well established that the presence of a spatially varying magnetization at a SC/FM interface can generate long range spin-polarized triplet supercurrents into the FM via the proximity effect in combination with spin mixing and spin rotation processes. Indeed junctions made up of Nb/Cr/Fe/Cr/Nb layers have been shown to carry supercurrents through significant thicknesses of Fe, showing that this combination of layers supports the generation of long range spin triplet superconductivity [1]. Quite separately, it has been recently demonstrated that spin pumping by ferromagnetic resonance (FMR) of Py when embedded in a Pt/Nb/Py/Nb/Pt stack also supports the formation of long range triplet superconductivity [2]. The characteristic signature of a spin triplet supercurrent in the latter case was an anomalous broadening of the FMR linewidth below the superconducting critical temperature (TC). In the current work we report on the FMR properties of Nb/Cr/Fe/Cr/Nb stacks, to study the behaviour of the intrinsic linewidth above and below TC and to establish characteristics indicative of triplet superconductivity. |
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T70.00179: Time-dependent Ginzburg-Landau model for light-induced superconductivity in the cuprate LESCO1/8 Ross Tagaras, Jian Weng, Roland Allen Cavalleri and coworkers have discovered evidence of light-induced superconductivity and related phenomena in several different materials [1]. Here we suggest that some features may be naturally interpreted using a time-dependent Ginzburg-Landau model. In particular, we focus on the lifetime of the transient state in La1.675Eu0.2Sr0.125CuO4 (LESCO1/8), which is remarkably long below about 25 K, but exhibits different behavior at higher temperature. A reciprocity inherent in the free energy makes the superconducting phase just as effective in blocking the stripe phase as vice-versa, and in the simulations at low temperature (coherent 3-dimensional) superconductivity persists as a robust metastable phase for an indefinitely long period of time after the femtosecond-scale laser pulse has destroyed the (coherent 3-dimensional) stripe phase. On the other hand, as the temperature, stoichiometry, and other parameters vary, there may be no ordered phase, or either, or both coexisting, as is consistent with a large body of experimental and theoretical work. |
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T70.00180: High field charge order across the phase diagram of YBa2Cu3Oy David LeBoeuf, francis laliberté, Mehdi Frachet, Siham Benhabib, Toshinao Loew, Juan Porras, Mathieu Le Tacon, Bernhard Keimer, cyril proust, steffen wiedmann In hole-doped cuprates there is now compelling evidence that inside the pseudogap phase, charge order breaks translational symmetry. In YBa2Cu3O y (YBCO) charge order emerges in two steps: a 2D order found at zero field and at high temperature inside the pseudogap phase, and a 3D order that is superimposed below the superconducting transition Tc when superconductivity is weakened by a magnetic field. Several issues still need to be addressed such as the effect of disorder, the relationship between those charge orders and their respective impact on the Fermi surface. Here, we report high magnetic field sound velocity measurements of the 3D charge order in underdoped YBCO in a large doping range. We found that the 3D charge order exists over the same doping range as its 2D counterpart, indicating an intimate connection between the two distinct orders. Moreover, our data suggest that 3D charge order has only a limited impact on low-lying electronic states of YBCO. |
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T70.00181: Pressure tuning of structure, superconductivity and novel magnetic order in the Ce-underdoped electron-doped cuprate T'-Pr_1.3-xLa_0.7Ce_xCuO_4 (x = 0.1) Zurab Guguchia, Tadashi Adachi, Zurab Shermadini, Johan Chang, Emil Bozin, Fabian O Von Rohr, Antonio M. dos Santos, Jamie Molaison, Reinhard Boehler, Yoji Koike, Jedrzej Wieteska, Benjamin Frandsen, Elvezio Morenzoni, Alex Amato, Simon J L Billinge, Yasutomo J Uemura, Rustem Khasanov High-pressure neutron powder diffraction, muon-spin rotation and magnetization studies of the structural, magnetic and the superconducting properties of the Ce-underdoped superconducting (SC) electron-doped cuprate system T'-Pr_1.3-xLa_0.7Ce_xCuO_4 with x = 0.1 are reported. A strong reduction of the lattice constants a and c is observed under pressure. However, no indication of any pressure induced phase transition from T' to T structure is observed up to the maximum applied pressure of p = 11 GPa. Large and non-linear increase of the short-range magnetic order temperature T_so in T'-Pr_1.3-xLa_0.7Ce_xCuO_4 (x = 0.1) was observed under pressure. Simultaneously pressure causes a non-linear decrease of the SC transition temperature T_c. All these experiments establish the short-range magnetic order as an intrinsic and a new competing phase in SC T'-Pr_1.2La_0.7Ce_0.1CuO_4. The observed pressure effects may be interpreted in terms of the improved nesting conditions through the reduction of the in-plane and out-of-plane lattice constants upon hydrostatic pressure. |
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T70.00182: Vortex structures in a mesoscopic unconventional superconductors Dae Han Park, Nammee Kim, Heesang Kim We investigate the vortex structures in unconventional superconductors of mesoscopic size. It is well-known that, in such small systems, the size as well as the shape have a profound influence on the formation of the vortex structure, leading to interesting phenomena such as giant vortex and anti-vortex. We present unusual vortex structures when the order parameters are unconventional and multi-dimensional. Especially, we focus on the vortex structures in mesoscopic unconventional superconductors. The results are compared with those in conventional ones. For concreteness, the order parameter which transforms according to the E1g representation of D6h is chosen. The vortex structures are obtained by minimizing the Ginzburg-Landau free energy, using the simulated annealing method. |
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T70.00183: Superconductivity in BiS2-based layered compound REO0.5F0.5BiS2 with high-entropy-alloy-type (HEA-type) blocking layers Yoshikazu Mizuguchi, Ryota Sogabe We have synthesized BiS2-based superconductors with high-entropy-alloy-type (HEA-type) REO (RE: rare earth) blocking layers [R. Sogabe et al., APEX 2018]. In the HEA-type samples, the RE site of REO0.5F0.5BiS2 was occupied with five RE elements with a compositional range of 5–35%. Notably, the superconducting properties were enhanced by making HEA-type REO blocking layer as compared to the BiS2-based superconductors with a conventional REO blocking layer. We will discuss about the interlayer interaction in the HEA-type REO0.5F0.5BiS2 superconductors by examining the samples having similar lattice parameters and different mixing entropy for the RE site. [R. Sogabe et al., 1808.04090] |
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T70.00184: MgB2 and NbTiN-based hyperbolic metamaterial superconductors Will Korzi, Grace Yong, Bryan Augstein, Wenura K Withanage, Fei Qin, Kanishka Wijesekara, Narendra Acharya, Xiaoxing Xi, Anne-Marie Valente-Feliciano, Joseph Prestigiacomo, Michael Osofsky, Igor Smolyaninov, Vera Smolyaninova Recent experiments have demonstrated that the metamaterial dielectric function engineering is capable of enhancing superconducting properties, such as tripling the critical temperature Tc in Al-Al2O3 epsilon near zero (ENZ) core-shell metamaterial superconductors. Similar effects have been observed in hyperbolic (superconductor/dielectric) metamaterials. In order to expand this approach to superconductors with higher Tc, MgB2/MgO, MgB2/AlN, and NbTiN/AlN multilayers were fabricated. Dielectric constants of these metamaterials measured via polarization reflectometry will be reported. Correlation of the results of the transport measurements and the hyperbolic properties of the multilayers will be discussed. |
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T70.00185: Non-centrosymmetric superconductivity in Re-based solid solutions Fabio Abud, Milton S Torikachvili, James Valles, Renato F Jardim Rhenium based superconducting compounds Re3M (M = W, Mo, Nb, Ta) crystallize in the non-centrosymmetric cubic α-Mn structure and have critical temperatures TC ranging from ~ 4 to 9 K. Polycrystalline samples of Re3M and its solid solutions were synthesized through an arc-melting furnace and subsequently heat treated at 1700 °C. Atomic substitutions of W by Ta or Nb in Re3W lead to single phase materials even in as-cast samples, a feature not observed in the parent compound. From the superconducting point of view, the low temperature heat capacity cp(T) data suggest conventional s-wave pairing, which is also supported by magnetization M(T), electrical resistivity ρ(T), and thermal conductivity κ(T) measurements. The estimated upper critical fields Hc2(0), however, are sizeable in comparison with the Pauli limiting field, and may be related to either a possible triplet channel or even disorder. Electron tunneling measurements of the superconducting density of states of Re3M materials are also presented to provide further insight into the superconducting pairing mechanism. The results are discussed within the context of the emergence of superconductivity in non-centrosymmetric materials. |
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T70.00186: Analysis of tunneling spectroscopy measurements of Assymetrical all-MgB2 Thin Film Josephson Junctions Joseph Lambert, Keeran Ramanathan, Masahito Sakoda, Michio Naito, Roberto Ramos We have previously reported high-resolution tunneling spectroscopy measurements of substructure within the two superconducting energy gaps of Magnesium diboride (MgB ) [1,2]. The samples used consisted of 1-gap/2-gap heterojunctions, where the counter-electrode is a conventional single-gap superconductor (Pb or Sn). Here, we report similar measurements of 2-gap/2-gap all-MgB Josephson junctions. The crystal orientations of the two MgB films are mostly c-axis parallel to the tunneling direction, with very small contribution from the larger σ gap. Due to differences in growth conditions, we find that the two MgB electrodes have different T 's and gap values. We represent this physical system using a modified tunneling model where each electrode is represented as a weighted sum of two BCS densities of states. We report results of this ongoing analysis that focuses on (1) a transition from SIS to NIS behavior as temperature increases past the lower Tc electrode, and (2) the presence of multiple quasiparticle peaks due to the sums and differences in pairwise combinations of disparate π and σ gap values within each electrode. |
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T70.00187: Possible three-dimensional nematic odd-parity superconductivity in Sr$_2$RuO$_4$ Wen Huang, Hong Yao The superconducting pairing in Sr$_2$RuO$_4$ is widely considered to be chiral $p$-wave with $\vec{d}_{\boldsymbol k} \sim (k_x + ik_y)\hat{z}$, which belongs to the $E_u$ representation of the crystalline $D_{4h}$ group. However, this superconducting order appears hard to reconcile with a number of key experiments. In this paper, based on symmetry analysis we discuss the possibility of odd-parity pairing with inherent three-dimensional character enforced by the inter-orbital interlayer coupling and the sizable spin-orbit coupling in the material. We focus on a yet unexplored $E_u$ pairing, which contains finite $(k_z \hat x$, $k_z \hat y)$-component in the gap function. Under appropriate circumstances a novel time-reversal invariant nematic pairing can be realized. This nematic superconducting state could make contact with some puzzling observations on Sr$_2$RuO$_4$, such as the absence of spontaneous edge current and no evidences of split transitions under uniaxial strains. |
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T70.00188: Rashba and Ising superconductors David Möckli, Maxim Khodas, Youichi Yanase, Manfred W Sigrist This poster addresses the parity-mixed superconductivity in a locally noncentrosymmetric multilayer system (Rashba), and in monolayer transition metal dichalcogenides (Ising). For the Rashba system, we investigate the magnetic field dependence of an ideal superconducting vortex lattice in the parity-mixed pair-density wave phase of multilayer superconductors within a circular cell Ginzburg-Landau approach. In multilayer systems, due to local inversion symmetry breaking, a Rashba spin-orbit coupling is induced at the outer layers. On the other hand, Ising materials like monolayer NbSe2 are nodal topological superconductors at magnetic in-plane fields exceeding the Pauli limit, with nodal points strictly on high symmetry lines in the Brillouin zone. We use a combined numerical and group-theoretical approach in real-space to characterize the unconventional superconducting state in monolayer transition metal dichalcogenides. Even with a conventional pairing interaction, the superconducting state is intrinsically parity-mixed and robust against on-site disorder. The interplay between the Zeeman magnetic field, strong spin-orbit interaction, and electronic orbital content confer the unique superconducting and topological properties. |
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T70.00189: Superconductivity in NbX2 Junye Huang, Deyi Fu, Barbaros Oezyilmaz NbX2, X=S, Se, Te is a family of superconducting transition metal dichalcogenides. Recently, the advent of 2D materials brought new insights into the study of superconducting TMDCs, such as gate tunability and layer dependence study, revealing rich interplay of charge density waves, spin orbit coupling and superconductivity. [1][2] Ising superconductivity arises in few-layer NbSe2 due to coexistence of SOC and superconductivity, showing strongly enhanced in-plane critical field [3] and 2nd order superconductor-insulator transition under in-plane magnetic field[4]. In this work, we explored the cousins of NbSe2 in the NbX2 family: NbS2 and NbTe2, using transport measurements down to milliKelvin. We will show magnetoresistance measurement in normal and superconducting states, as well as angle dependence of critical field. |
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T70.00190: STRONGLY CORRELATED SYSTEMS, INCLUDING QUANTUM FLUIDS AND SOLIDS
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T70.00191: Magnetoelastic coupling in multiferroic CaBaCo4O7 Barnita Paul, Rajeev Gupta A large change in magnetic field induced polarization of ΔP ~8 mC/m2 around TC was discovered in multiferroic CaBaCo4O7 suggesting a giant linear magnetoelectric effect. The crystal structure of CaBaCo4O7 contains alternating triangular and kagome layers along c axis with distorted corner shared CoO4 tetrahedra that makes these oxides a unique class of geometrically frustrated systems. It is assumed that the large magnetoelectric coupling arises from their atypical crystal structure and the mixed valence state of Co cations. It is well known that specific spin-lattice interaction can control the direction of the electrical polarization with a magnetic field. Although strong magnetoelastic coupling is expected in these improper ferroelectrics, there are hardly any studies to investigate the same. In this work we carry out a detailed investigation on magnetoelastic coupling using temperature dependent Raman measurements. We observe anomalous deviation of phonon frequencies and line-width from anharmonicity in the magnetic ordered phase. The maximum deviation is observed across Tc. This study suggests a strong magnetoelastic coupling in this compound in the ferrimagnetic phase and indicates the role of lattice in the gigantic spin induced polarization along c axis. |
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T70.00192: Spin-orbital-lattice entangled states in cubic d1 double perovskites Naoya Iwahara, Veacheslav Vieru, Liviu F Chibotaru The magnetism of cubic 4/5d1 double perovskites has been intensively investigated due to their geometrical frustration and multipolar exchange interaction, whereas many puzzling phenomena related to the lattice degrees of freedom, e.g. “violation of the JT theorem” in structural data [1] and “breaking of local point symmetry” accompanying the ferromagnetic order [2], have not been understood. In this work, the interplay of spin-orbit coupling and vibronic coupling on the heavy d1 site is investigated by ab initio calculations [3]. The stabilization energy of spin-orbital-lattice entangled states is found to be comparable to or larger than the exchange interactions, suggesting the presence of nonadiabatic Jahn-Teller dynamics in the systems. The entanglement of the spin and lattice degrees of freedom induces a strong magnetoelastic response. This multiferroic effect is at the origin of the recently reported breaking of local point symmetry accompanying the development of magnetic ordering in Ba2NaOsO6. |
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T70.00193: Spin Seebeck Effect in insulating SrFeO3-δ films Deshun Hong, Changjiang Liu, JOHN E. PEARSON, Axel F Hoffmann, Dillon D Fong, Anand Bhattacharya
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T70.00194: Quantum percolation of monopoles and the response of quantum spin ice Vadim Oganesyan, Matthew Stern, Claudio Castelnovo, Sarang Gopalakrishnan The low temperature (magnetic) response of quantum spin ice is dominated by the coherent motion of a dilute gas of monopoles. Contrary to conventional modelling that assumes a uniform distribution of hopping amplitudes for such dynamics, recent work by Tommasello et al. has demonstrated that the distribution is in fact bimodal, and strongly correlated with the surrounding spin configuration. The larger of the two amplitudes occurs on average 2/3 of the times, and is responsible for the coherent motion of monopoles. The smaller one, on the other hand, induces dynamics that is far slower than the expected decoherence time scales in a solid state system. We exploit this structure to construct a theory of quantum monopole motion in spin ice in the limit where the slow hopping terms are set to zero. The monopole wavefunctions are fractal. The non-ergodic nature of monopole motion manifests itself in the low-frequency behaviour of spin response, and is consistent with experimental observations. We further extend our results to the case of disordered spin ice. |
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T70.00195: Many-body-localization transition in the one-dimensional SYK model at finite N Xin Dai, Shaokai Jian, Hong Yao We study the generalized Sachdev-Ye-Kitaev (SYK) chain consisting of N (complex or Majorana) fermions per site with random interactions and hoppings between neighboring sites. In the limit of vanishing SYK interactions, from both supersymmetric field theory analysis and numerical calculations we find that the random-hopping model exhibits Anderson localization at finite N, irrespective of the parity of N. Moreover, the localization length scales linearly with N, implying the absence of Anderson localization only at N=∞. For finite SYK interactions, by performing the exact diagonalization we show that there is a dynamic phase transition from many-body localization to thermal diffusion as interaction strength exceeds a critical value Jc. In addition, we find that the critical interaction strength Jc decreases with the increase of N, consistent with the analytical result of Jc/t ∝ 1/(N^5/2logN), derived from the weakly interacting limit. |
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T70.00196: Electrically conducting rock-salt LuO epitaxial thin film Kenichi Kaminaga, Daichi Oka, Tetsuya Hasegawa, Tomoteru Fukumura Lutetium sesquioxide Lu2O3 is known as a widegap insulator with the highly stable closed shell trivalent ions. On the other hand, lutetium monoxide LuO has been recognized as gaseous phase. In this study, solid-phase rock-salt LuO was synthesized in a form of epitaxial thin film by pulsed laser deposition method for the first time [1]. LuO possesses unusual valence of Lu2+ (4f145d1). In contrast with transparent and highly insulating Lu2O3, LuO exhibited dark-brown color and metallic conduction with high electrical conductivity at room temperature (~60 S.cm–1). A cusp-shaped positive magnetoresistance originating from the weak antilocalization effect suggested a significant spin-orbit coupling in LuO manifested by Lu 5d electron carriers. [1] K. Kaminaga et al., ACS Omega 3, 12501-12504 (2018). |
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T70.00197: Structure-property relationships in lacunar spinels from band theory Yiqun Wang, James M Rondinelli The A-site deficient lacunar spinel GaM4X8 (M=Mo,V,Nb,Ta; X=S,Se) are ideal candidates to achieve novel electrical materials exhibiting metal-insulator transitions and may find use in resistive random-access memories (RRAM). They are experimentally narrow-bandwidth semiconductors, and undergo structural, electrical and magnetic phase transitions with external stimuli, e.g. temperature, pressure, electric pulse. |
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T70.00198: High-pressure synthesis, crystal structure, and magnetic properties of Ba3CuOs2O9 Jie Chen, Hai Luke Feng, Yoshitaka Matsushita, Alexei A Belik, Yoshihiro Tsujimoto, Yoshio Katsuya, Masahiko Tanaka, Man-Rong Li, Hongbin Liang, Lirong Zheng, Kazunari Yamaura The triple perovskite Ba3CuOs2O9 crystalizes into an orthorhombic structure (Cmcm ) and shows a manifest antiferromagnetic transition at 47 K [1], while it crystalizes into a hexagonal structure (P63/mmc) when treated under a high-pressure and high-temperature condition (typically 6 GPa and 1100 ○C). The change of structure gains a 1.3% increase in structural density. The hexagonal phase was quenched at ambient condition and the magnetic and electrical properties were investigated via measurements of the ac and dc magnetic susceptibilities, electrical resistivity, and specific heat capacity. The data indicated that the magnetic transition temperature increased to 290 K by the structure change. We discuss details of the magnetic and electrical properties of the newly synthesized hexagonal Ba3CuOs2O9. |
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T70.00199: WITHDRAWN ABSTRACT
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T70.00200: Electronic Transport in Thin Crystals of Ruthenium Chloride Naomy Marrufo, Amirari Diego, Josue Rodriguez, Gilbert Lopez, Nicholas Breznay, Robert Kealhofer, Francisco Ramirez, Samantha Crouch, James G. Analytis, Claudia Ojeda-Aristizabal Ruthenium chloride (RuCl3) has gathered significant interest in the recent years, as it is a layered |
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T70.00201: Doping driven spin-flop transition in mixed 3d-5d compounds Weiguo Yin, Wenhu Xu, Robert Konik The in-plane magnetization of the layered iridate Sr2IrO4 turns to out-of-plane upon partial substitution of ruthenium or manganese atoms for iridium. Based on first-principles electronic structure analysis, we present an effective low-energy Hamiltonian to model this doping effect. We found that the spin-flop transition originates from the M-Ir bond direction changes from the local easy axis to the hard axis as M changes from Ir to Ru or Mn. |
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T70.00202: Semi-classical Theory of Large N Tensor Model Chaos Jaewon Kim, Ehud Altman, Thomas Scaffidi Lately, the Sachdev-Ye-Kitaev (SYK) model has become increasingly important due to its chaotic dynamics and its approximate conformal symmetry. The model’s conformal symmetry suggests the existence of a holographic dual, rendering the model important in the study of quantum gravity. Tensor models have been found to be similar to the SYK model, in that they exhibit the dominance of melonic diagrams. In this paper, we study the chaotic dynamics of the Tensor Models semi-classically, by finding the spectrum of the Lyapunov exponent. We introduce a classical version of the Tensor model for which chaos can be understood as arising from nonlinear dynamics of the equation of motion. |
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T70.00203: 2D fermi gases under the microscope Airlia Shaffer-Moag, Cedric Wilson, Biswaroop Mukherjee, Parth Patel, Zhenjie Yan, Richard J Fletcher, Martin Zwierlein Confining a quantum fluid in two dimensions (2D) profoundly changes its behavior and leads to a host of new phenomena, for example the possibility of topological superfluid transitions and quantum Hall states. Here we report our progress towards creating a uniform 2D fermionic gas of 6Li confined in a highly flexible optical potential. The homogenous density enables the study of physics typically difficult to access in harmonically trapped samples, such as critical phenomena, correlation functions, superfluid properties and the spectroscopic response. Incorporating a dual-objective high-resolution imaging system allows us to both manipulate and image the gas with sub-micron resolution, permitting the projection of tailored potentials and in situ imaging of topological defects. |
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T70.00204: Machine learning of quantum phase transitions Xiaoyu Dong, Xuefeng Zhang, Frank Pollmann Machine learning algorithms provide a new perspective on the study of physical phenomena. In this paper, we explore the nature of quantum phase transitions using multi-color convolutional neural-network (CNN) in combination with quantum Monte Carlo simulations. We propose a method that compresses (d + 1)-dimensional space-time configurations to a manageable size and then use them as the input for a CNN. We test our approach on two models and show that both continuous and discontinuous quantum phase transitions can be well detected and characterized. Moreover we show that intermediate phases, which were not trained, can also be identified using our approach. |
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T70.00205: Unbinding slave spins in the Anderson impurity model Daniele Guerci, Adriano Amaricci, Michele Fabrizio We show that a generic single-orbital Anderson impurity model, lacking, for instance, any kind of particle-hole symmetry, can be exactly mapped without any constraint onto a resonant level model coupled to two Ising variables, which reduce to one if the hybridization is particle-hole symmetric [1]. The mapping can be straightforwardly extended to a multiorbital impurity model where the isolated impurity Hamiltonian does not include Coulomb exchange terms. We also demonstrate how single-particle Green’s functions of the physical fermions can be calculated without constraints, which would, for instance, allow exploiting DMFT to study in the slave-spin representation Hubbard-like models in lattices with infinite coordination. The generality of the mapping allows to study a wide range of problems varying from the Mott-transition in infinite-dimensionality to transport in quantum dots. |
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T70.00206: ABSTRACT WITHDRAWN
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T70.00207: Local electrodynamics of disordered conductor model systems measured with scanning microwave impedance microscopy Holger Thierschmann, Hale Cetinay, Matvey Finkel, Marc P. Westig, Allard J. Katan, Piet van Mieghem, Teun M Klapwijk We have measured the local impedance of disordered conductor model systems at GHz frequencies in order to study the electrodynamic response of systems around the metal-insulator phase transition for non-trivial patterns of conductive and insulating regions at small scales. We realize the disordered conductors through nano patterning of metallic thin films into networks which exhibit a phase transition from the conducting to the insulating state through bond percolation. The electrodynamic response is measured with a scanning microwave impedance microscope at room temperature. When the networks are patterned out of aluminum with highly conductive bonds, we observe a correlation of the local signal and the size of the respective cluster, at different degrees of percolation. When the bonds are made more resistive through using NbTiN, the signal varies within a cluster, depending sensitively on the local network topology. Our results are well reproduced within a network model of resistors and capacitors that takes into account the specific network topologies as well as the electric and dielectric environment. |
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T70.00208: Mesoscopically confined 2D holes with strong correlation Chieh-Wen Liu, Loren Pfeiffer, Kenneth West, Xuan Gao We present a transport study on the mesoscopic confinement effects on a strongly interacting two-dimensional holes (2DH) in a GaAs quantum well with low density (~2×1010/cm2) and high mobility. By applying a voltage to a split-gate, the 2DH underneath the gate is depleted, leaving a narrow (~2 μm wide) channel conducting. The channel formation is reflected in the evolution of the temperature (T)-dependent resistance at various gate voltages Vg as well as the Vg dependent resistance. Interestingly, when the mesoscopic channel starts to form, a strong magneto-resistance peak with an insulating-like T dependence was observed before the ν =1 quantum Hall (QH) state. When the channel is further depleted, the magnetic field induces a rapidly increasing magneto-resistance and a 'metal-to-insulator' transition appears at a moderate magnetic field (~ 0.2 T) where the sample resistivity ρxx << h/e2 along with the destruction of the ν =1 QH state. Our results suggest that mesoscopically constricted dilute 2D systems can be a rich playground for exploring interaction effects and phase transitions in 2D. |
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T70.00209: Optical control of magnetism in NiFe/VO2 heterostructures Guodong Wei, Xiaoyang Lin, Stephane Mangin, Weisheng Zhao Optical methods for magnetism manipulation have been considered as a promising strategy for ultralow-power spintronics. Strategies based on all optical switching (AOS), hot electrons and photosensitive-material-based devices have already generated exciting new prospects both for fundamental physics and technological applications. However, a widely applicable method to combine optical operation with magnetic modulation is still highly desired. Here, the strongly correlated electron material VO2 is introduced to realize phase-transition based optical control of the magnetism in NiFe. [1] The heterostructure features appreciable modulations both in electrical and magnetic properties. Utilizing this optically controlled magnetism modulation feature, programmable Boolean logic gates (AND, OR, NAND, NOR, XOR, NXOR and NOT) for high-speed and low-power data processing are demonstrated based on this engineered heterostructure. As a demonstration of phase-transition spintronics, this work may pave the way for next-generation electronics in the post-Moore era. |
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T70.00210: Thermodynamic signatures of the field-induced states of graphite David LeBoeuf, C.W. Rischau, gabriel Seyfarth, R. Küchler, steffen wiedmann, W. Tabis, Mehdi Frachet, benoit fauqué, Kamran Behnia When a magnetic field confines the carriers of a Fermi sea to their lowest Landau level, electron−electron interactions are expected to play a significant role in determining the electronic ground state. Graphite is known to host a sequence of magnetic field-induced states driven by such interactions. Three decades after their discovery, thermodynamic signatures of these instabilities are still elusive. Here we report the detection of these transitions with sound velocity measurements. The evolution of elastic constant anomalies with temperature and magnetic field allows to draw a detailed phase diagram which shows that the ground state evolves in a sequence of thermodynamic phase transitions. Our analysis indicates that the electron−electron interaction is not the sole driving force of these transitions and that lattice degrees of freedom play an important role. |
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T70.00211: Tuning low temperature electrical resistivity in TiSe2 Jaime Moya, Jesse Choe, Chien-Lung Huang, Emilia Morosan TiSe2 has been one of the most studied and debated transition metal dichalcogenides in part due to an indirect band gap/overlap that is difficult to resolve. It has been known for some time that dilute impurities and growth conditions can drastically affect the transport properties of TiSe2. Much attention has been paid to the anomalous feature in temperature dependent resistivity near 150 K where a charge-density-wave transition forms, but there has been little reported on the low temperature resistivity, where there is large discrepancy between polycrystalline and single crystalline samples. We confirm the metallicity in single crystalline TiSe2 grown by the chemical vapor transport method is caused by dilute iodine as a transport agent during growth, which gives rise to formation of impurity bands near the Fermi surface. On the other hand, the polycrystalline sample synthesized by solid state reaction without extrinsic additives shows intrinsically insulating ground state of TiSe2. Furthermore, we demonstrate the ability to tune the insulating behavior of TiSe2 with different synthesis parameters. |
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T70.00212: Probing uniaxial strain effects on SmB6 using 11B solid-state nuclear magnetic resonance Yue-Shun Su, Yongkang Luo, Andrej Pustogow, Eric Bauer, Stuart E Brown The strongly-correlated and mixed valence Kondo insulator SmB6 has been shown to exhibit surface states, which are suggested to originate with non-trivial topology. The surface state conduction is observed to dominate over bulk conduction only at Li-He temperatures. However, recently reported results from transport measurements were interpreted as evidence for surface-dominated transport to temperatures as high as 240 K, consistent with a much larger bulk gap. 11B NMR relaxation measurements were carried out under strained conditions, as a means for studying at a microscopic level the gap evolution, and in search for evidence of a heterogeneous phase. In initial measurements, the behavior is consistent with a 50% increase in energy gap with only 0.5% uniaxial strain; experiments at higher strain are underway. |
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T70.00213: Topological properties of CeNiSn, CeRhAs, and CeRhSb: hourglass-type crossing and Dirac nodal-loop bulk band structure Taesik Nam, Chang-Jong Kang, Dong-Choon Rhyu, Junwon Kim, Heejung Kim, Kyoo Kim, Byung Il Min Topological Kondo insulators draw a great deal of recent attention, and so research on conventional Kondo insulators is actively revived. SmB6 is a typcial example. Among Ce-based systems, CeNiSn, CeRhSb, and CeRhAs were recently predicted to have exotic topological surface states that has been intensively studied by electrical resistivity and optical conductivity measurement. To investigate whether these materials are promising candidate of topological Kondo insulators, we have investigated the electronic structures of CeNiSn, CeRhSb, and CeRhAs, employing the density functional theory and the dynamical mean field theory (DMFT). For all three systems, we have obtained the hourglass-type bulk band crossings around k=S, which produce a Dirac nodal-loop centered at S in the [100] BZ boundary. This nodal-loop band crossing is guaranteed by crystal symmetry. In addition, from the DMFT calculations, we have found that the hourglass-type band structure along X-S line penetrates through the Ce f-level near the Fermi energy, resulting from the hybridization effect between the different characters of bands. This gives the possible change of topological property upon T variation. This work introduces new type of nodal-loop Dirac semimetal, especially when f level is involved in the system. |
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T70.00214: Exploring "hidden order" (HO) through Re and Rh co-substitution in URu2Si2 Kalyan Sasmal, Sheng Ran, Trevor Keiber, Bob Wang, Robert A Robinson, M Brian Maple The identity of the mysterious “hidden-order” (HO) phase in the correlated f-electron superconductor (SC) URu2Si2 has eluded researchers for more than three decades. Substitution of transition metals into URu2Si2 at the Ru sites reveals how factors such as lattice parameters, charge carrier concentration, disorder and d-f electron hybridization influence the HO phase and SC. We discuss the effects of the co-substitution of equal amounts of Re and Rh, which are isoelectronic on average, into URu2Si2 to form URu2-2xRexRhxSi2, pseudo ternary alloys based on the physical properties including structure and lattice parameters, electrical resistivity, magnetic susceptibility, and specific heat. The features in the physical properties that characterize the energy gap associated with the HO phase (e.g., exponential T-dependence of the specific heat) are suppressed rapidly with Re and Rh co-substitution level so that by x = 0.11, the HO phase transition is no longer discernible. The HO phase transition temperature (THO) and the gap decrease monotonically with Re-Rh concentration x. |
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T70.00215: A Dirac Fermion Hierarchy of Composite Fermi Liquids Jie Wang Composite Fermi liquids (CFLs) are compressible states that can occur for 2D interacting fermions confined in the lowest Landau level at certain Landau level fillings. They have been understood as Fermi seas formed by composite fermions which are bound states of electromagnetic fluxes and physical fermions due to the celebrated work by Halperin, Lee and Read [Phys. Rev. B 47, 7312 (1993)]. At half filling, an explicitly particle hole symmetric theory based on Dirac fermions [Phys. Rev. X 5, 031027 (2015)] was proposed by Son as an alternative low energy description. In this work, we propose an effective theory, which generalizes Son’s Dirac fermion theory, by internal gauge flux attachment, from half filling to all fillings that CFLs for fermions can occur. We also numerically investigated the Berry curvature of CFL model wave functions at fillings not being one half, and observed that it is uniformly distributed on the Fermi sea except at the center where an additional π phase was found. The numerical results support the idea of internal gauge flux attachment. |
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T70.00216: First-principles study of charge and magnetic ordering in monolayer NbSe2 Zhimou Zhou, Feipeng Zheng, Xiaoqiang Liu, Ji Feng Monolayer NbSe2 has recently been shown to be a two-dimensional superconductor, with a competing charge-density wave (CDW) order. This work investigates the electronic structure of monolayer NbSe2 based on first-principles calculations, focusing on charge and magnetic orders. It is found that decreased screening in the monolayer NbSe2 with a perfect lattice exhibits magnetic instability, which is removed by the formation of CDW. Two energetically competitive but distinct 3 × 3 CDW structures are revealed computationally, which have a significant impact on the Fermi surface. The relations of the potential CDW phases with experimental structure and the coexisting superconductivity are discussed. |
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T70.00217: Fermionic retro reflection, hole jets. and magnetic steering in 2D electron systems Lev Kendrick, Patrick J. Ledwith, Andrey Shytov, Leonid Levitov The combination of fermion exclusion and momentum conservation leads to unusual dynamics in two-dimensional Fermi liquids. We show that the response of a 2D Fermi liquid to an injected beam of current includes hole jets centered at the backscattering direction. We propose a magnetotransport measurement to probe the angular structure of the hole jets. |
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T70.00218: SmB6 in-gap states encoded inside the hybridization Edwin Ramos, Jereson Silva Valencia, Roberto Franco, Marcos Figueira In this article we investigate the effects of short-range anti-ferromagnetic correlations on |
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T70.00219: Quantum effects in the system of Boltzmann hard spheres Sergei Stishov The quantum contribution to the energy of the Boltzmann gas of solid spheres turns out to be practically constant to the highest temperatures, when the De Broglie thermal wavelength is only a small fraction of the diameter of the solid sphere. Accordingly, the heat capacity of the system is not much different from the classical value of 3/2 k everywhere except for the region of the lowest temperatures, where the dependence of the heat capacity of the system on temperature has a Debye appearance, but with a very low "Debye" temperature of the order of several degrees. |
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T70.00220: Spontaneous symmetry breaking from anyon condensation Marcel Bischoff, Corey Jones, Yuan-Ming Lu, Dave Penneys As a cornerstone for condensed matter physics, Landau theory of symmetry breaking dictates that the symmetry group G of a physical system can spontaneously breaks down to any subgroup H, characterized by a local order parameter valued in the quotient group G/H. However this paradigm breaks down when topological orders and anyons come into play. What is the relation between symmetry groups G and H of two symmetry enriched topological orders (SETOs), if they are connected to each other through a continuous quantum phase transition (QPT)? To address this issue, we develop a mathematical framework within the category theory of topological orders, which determines the compatibility of symmetry groups G and H for two SETOs connected by a QPT driven by anyon condensation. We identify two symmetry obstructions for such anyon-condensation transitions. which are demonstrated by many examples. |
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T70.00221: Identification of low-lying energy states in quantum critical Ce(Fe0.76Ru0.24)2Ge2 Thomas Heitmann, Wouter Montfrooij, Yiming Qiu, Shannon M Watson, Ross Webb Erwin, Wangchun Chen, Yang Zhao The compound Ce(Fe0.76Ru0.24)2Ge2 has long been known to be a quantum critical point system. One of the features discovered in this material is hyperscaling of the dynamic response of the system. Chemical doping is used to prepare the system at the quantum critical point, which results in a distribution of local Kondo temperatures and consequently the formation of magnetic clusters. We present direct evidence for the spin-flipping of these magnetic clusters, which provides the low energy states required to explain the hyperscaling at the quantum critical point. The superspin flipping was first identified using spin-polarized neutron spectroscopy on the BT7 triple-axis spectrometer at the NIST Center for Neutron Research, then—once the magnetic signal was separated from that of the lattice—tracked using unpolarized neutron spectroscopy on the TRIAX thermal neutron triple-axis spectrometer at the University of Missouri Research Reactor. |
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T70.00222: Braiding of worldlines in Monte Carlo configurations as nonlocal probe for quantum phase transitions Liana Shpani, Wei Wang, Fabio Lingua, Barbara Capogrosso-Sansone We propose to use the braiding of particles' trajectories in path-integral Monte Carlo configurations, to characterize entanglement “patterns” in strongly-correlated hardcore lattice bosons. By extracting certain statistical properties of worldline configurations, we are able to detect the SF-insulator transition and SF-Z2 topological insulator transition. |
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T70.00223: Ultrafast transient interference in pump-probe spectroscopy of band and Mott insulators Kazuya Shinjo, Takami Tohyama Ultrafast pump-probe spectroscopy with high temporal and spectral resolutions provides new insight into ultrafast nonequilibrium phenomena. We propose that transient interference between pump and probe pulses is realized in pump-probe spectroscopy of band and Mott insulators, which can be observed only after recent developments of ultrafast spectroscopic techniques [1]. A continuum structure in the excitation spectrum of band insulators is found to act as a medium for storing the spectral information of the pump pulse, and the spectrum detected by the probe pulse is interfered with by the medium, generating the transient interference in the energy domain. We also demonstrate the transient interference in the presence of electron correlations in a one-dimensional half-filled Hubbard model. Furthermore, bosons coupled to electrons additively contribute to the interference. Our finding will provide an interpretation of probe-energy-dependent oscillations recently observed in the pump-probe spectrum for a two-dimensional Mott insulator [2]. |
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T70.00224: Dynamical t/U Expansion Theory of a Doped Hubbard Model Wenxin Ding, Rong Yu In this work, we construct a new U(1) slave representation for the single band Hubbard model in the large-U limit. By employing a dynamic Green's function method for the slave spins, we formulate a dynamic t/U expansion for the Hubbard model which reduces the model to a t-J-type low energy effective theory for the spinons and an XXZ-type effective theory for the slave spins. This new approach recovers our previous slave rotor results for the Mott insulating state at half-filling, and is more amenable to describe the strong correlation effects in the finite doping regime. By solving the slave spin theory at the mean field level for finite doping, we find that the superexchange interaction strength J, as well as the effective spinon hopping amplitude, develops doping dependence. More interestingly, pairing-type interaction in the dynamic Green's function shows up, which solely stems from quantum fluctuations of the doping driven Mott-insulator-to-metal transition. |
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T70.00225: COMPLEX STRUCTURED MATERIALS, INCLUDING GRAPHENE
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T70.00226: Energy-Momentum Photoluminescence Spectroscopy of Quantum Emitters in Hexagonal-Boron Nitride Yang Wang, Juan Lizarazo Ferro, Rashid Zia Defects in hexagonal-boron nitride(h-BN) have recently been characterized and identified as light emitters that are ideal for quantum information applications. These photostable emitters have narrow and tunable emission spectra, operate at room temperature, and exhibit high quantum efficiency. However, the electronic structure of these quantum emitters are still under intense debate. In this presentation, we use angle- and polarization-resolved photoluminescence spectra to study the origin of light emission from a range of point emitters in h-BN. |
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T70.00227: Visualization of domain and interfacial structures of Monolayer semiconductors by Nonlinear Optical Microscopy Chun An Chen, Ying-Yu Lai, Po-Yen Lin, Xin-Quan Zhang, Meng-Hsi Chuang, Yi-Hsien Lee Domain and interfacial structures of the monolayer transition metal dichalcogenides (TMD) are significant to diverse physics and performances. Unique carrier transportation and bandgap tunability could be engineered with inter-grain twisting, which provide an extra degree of freedom for device designing. Here, the correlation between GBs and inter-grain twisting in monolayer WS2 is studied using nonlinear microscopy. With the change of inter-grain twisting, domain and interfacial structures of the monolayer is monitored and studied. |
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T70.00228: Energy transfer in van der Waal stacked MoS2 – Graphene Quantum Dots with Ab-initio validation Rajarshi Roy Graphene based van der Waals (vdW) heterostructures can facilitate enticing charge transfer dynamics in between the layers with emission of excitonic quasi-particles. In this work, an attempt has been made to probe such van der Waal (vdW) heterostructures between few layer MoS2 sheet embedded quantum dot (QD) and amine-functionalized graphene quantum dot (GQD) to explore the energy transfer mechanism. Our findings reveal interesting non-radiative Forster type energy transfer with quenching of functional GQD PL after GQD/MoS2 hetero interface formation and validates the existing charge transfer shown that is analogous between a 0D and 2D system. This non-radiative type energy transfer characteristics from GQD into MoS2 layer through vdW interaction has been confirmed by with a combination of photoluminescence and time decay analyses with ab-initio calculation affirms the same observation with shifting of Fermi level in density of states towards conduction band in van der Waals distance separation limit. This result encourage exploration of optical properties in other QD/2D based heterostructures for understanding the charge transfer mechanism and luminescence quenching for future optoelectronic device and optical sensing applications. |
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T70.00229: When graphene meets electrolyte: how does graphene sense proton (H+)? Xiaoyu Jia, Zhaoyang Liu, Zongping Chen, Akimitsu Narita, Müllen Klaus, Klaas-Jan Tielrooij, Mischa Bonn, I. Hai Wang Graphene has been extensively used as electrodes in electrochemical applications [1,2,3]. Despite its relevance for these various applications of graphene, the effect of electrolyte solutions on the electronic properties, specifically conductivity, of graphene remains poorly understood. In the few available studies using graphene field effect transistors (FETs) for ionic sensing, conflicting results have been reported [4,5]. One major challenge is to separate contributions to the overall FET conductance from bulk electrolyte conductivity and from graphene itself, as the FET contacts are typically also exposed to the electrolyte. Here we introduce THz spectroscopy as a contact-free, all optical means to track the intrinsic carrier conductivity of silica-graphene in contact with protons (H+) in water. Our report provides new insight on the graphene’s proton sensing mechanism, and highlights the importance and impact of proton transfer though graphene and interfacial charge screening on the graphene conductivity enhancement. |
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T70.00230: Thermal conductivity of TMPS3 (TM=Fe, Ni, and Mn): role of a boundary scattering Hwiin Ju, Younggwan Choi, DoGyeom Jeong, Sungmin Lee, Je-Guen Park, Jongseok Lee Among various van der Waals (vdW) materials, a TMPS3 (TM=Fe, Ni, Mn) group undergoes an antiferromagnetic transition at about 100 K, and hence can be an important magnetic layer in realizing multi-functional heterostructure. Although a thermal conduction through vdW materials is a fundamental issue in optimizing device performances, thermal properties of TMPS3 has rarely been studied. In this work, we measured the thermal conductivity of TMPS3 materials with a time-domain thermoreflectance method. We found that the cross-plane thermal conductivity of TMPS3 is relatively low compared to other vdW materials, such as graphite and transition-metal dichalcognides. By comparing the temperature–dependent thermal conductivities of these materials, we demonstrated that effective boundaries caused by a stacking fault of vdW layers act as a main scattering channel in the heat conduction in these materials. |
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T70.00231: Transition metal dichalcogenide phase-change materials for infrared photonics Akshay Singh, Yifei Li, Jian Zhou, Heshan Yu, Ichiro Takeuchi, Ju Li, Rafael Jaramillo Transition metal dichalcogenides (TMD) exist in 2H (usually semiconducting) and 1T’ (semi-metallic) polymorphs. Switching between these polymorphs offers a new paradigm for controlling light. However, energy required for phase-change (PC) in pure phases is large. Alloying 2H and 1T’ materials, for example MoS2 and TiS2, could offer low-energy PC. This low energy transformation would especially be useful for infrared (IR) integrated photonics. |
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T70.00232: Large area synthesis of GaSe and GaS monolayers by Chemical Vapor Deposition Algene Fyer, Tariq Afaneh, Humberto Rodriguez Gutierrez Two-dimensional crystals of group-III metal monochalcogenides [i.e. MX where M={In, Ga} and X={S, Se,Te}] have gained attention in the last years as alternative 2D semiconductors. They present high carrier mobility, thickness dependent electronic properties, as well as good photoresponse and on/off ratio. To date, most of the fundamental studies in these materials have been performed on mechanically exfoliated samples and few groups have reported chemical vapor deposition (CVD) synthesis of these materials. The implementation of practical electronic applications will rely on developing approaches to deposit high quality films over large areas. The CVD approaches reported to date usually involve low pressure environment and MX powders with the right stoichiometry (pre-synthesized in vacuum sealed ampules) used as evaporation sources, as well as. Here we report large area deposition of GaSe and GaS monolayers, using atmospheric pressure CVD and commercially available precursors. We systematically studied the influence of the growth parameters on the quality of the as grown materials. The samples were characterized using micro-Raman spectroscopy, scanning electron microscopy and atomic force microscopy. |
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T70.00233: A Novel Method for Thermal Conductivity Measurements in Atomically Thin Materials Talip Kasirga, Onur Çakiroğlu, Hamid Reza Rasouli Study of thermal properties of materials are crucial for applications and fundamental science. There are many techniques available in the literature to measure thermal conductivity. Measuring the thermal conductivity of atomically thin materials however, is a major challange. The most common method is to measure the temperature calibrated shift of a well-defined Raman peak with increasing laser power over a suspended sample.The a fit to the measured data with a temperature profile yields the thermal conductivity. Applicability of this method is limited to materials with relatively low thermal conductivity and well established Raman peaks. In this presentation, I will talk about the method we developed for measuring the thermal resistivity of atomically thin materials relies on a laser beam and two terminal resistivity measurement. The technique can be applied to any conductive material. |
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T70.00234: Origin of anisotropic negative Poisson's ratio in graphene Zhenzhen Qin, Guangzhao Qin, Ming Hu Negative Poisson's ratio (NPR) in auxetic materials is of great interest due to the typically enhanced toughness, shear resistance, and sound and vibration absorption, which enables plenty of novel applications such as aerospace and defense. Insight into the mechanism underlying NPR is significant to the design of auxetic nanomaterials and nanostructures, and a thorough and fundamental understanding is lacking. In this paper, we report anisotropic differential NPR in graphene for uniaxial strains applied along both zigzag and armchair directions based on first-principles calculations. The mechanism underlying the emergence of NPR in graphene (evolution of bond length and bond angle) is found to be different from the conclusions from previous classical molecular dynamics simulations with empirical potential. We propose that the decentralized electron localization function (ELF) driven by strain leads to ELF coupling between different types of bonds, which results in the counter-intuitive anomalous increase of the bond angle and thus the emergence of NPR in graphene. Moreover, the NPR phenomenon can be anticipated to emerge in other nanomaterials or nanostructures with a similar honeycomb structure as that of graphene, where the ELF coupling would also be possible. |
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T70.00235: Magnetic doping of 2D semiconductor crystals Nalaka Kapuruge, Vijaysankar Kalappattil, Florence A Nugera, Manh-Huong Phan, Humberto Rodriguez Gutierrez Recently reported ferromagnetism in two dimensional crystals have gain increasing interest due to its potential for developing a new generation of 2D spintronic devices. Doping transition metal dichalcogenides with magnetic atoms such as Cr, Mn and Fe, is another approach worth exploring. High doping levels can lead to 2D diluted magnetic semiconductors with crystalline structure compatible with the TMDs that can be connected laterally to create in-plane lateral heterostructures with potential for spin valves or spin-FETs applications. In this work, we report on the Mn magnetic doping of Transition metal dichalcogenides (e.g MoSe2) using a chemical vapor deposition approach. The optical properties of the as grown films were studied by micro-Raman and PL spectroscopy. Morphology and thickness of the samples were characterized via SEM and AFM, respectively. The samples display room-temperature magnetism and a clear temperature dependent ferromagnetic characteristic. |
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T70.00236: Electronic and Structural Properties of Defects in Few Layer Molybdenum Disulfide Films Marcus Forst, Dan Trainer, Marian Precner, Tomas Polakovic, Qiao Qiao, Yimei Zhu, Xiaoxing Xi, Goran Tripun Karapetrov, Maria Iavarone Molybdenum disulfide (MoS2) has emerged as an attractive candidate for next-generation 2D electronic devices yet the exact role of defects on its electronic properties is still not well understood. In this study we employ scanning tunneling microscopy and spectroscopy, transmission electron microscopy and kelvin probe force microscopy to obtain quantitative measurements of the local density of states, work function and nature and mobility of these defects. The defects investigated include individual point defects such as sulfur and molybdenum vacancies and extended defects like grain boundaries and film edges. |
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T70.00237: Inversion-domain-free growth of epitaxial MoS2 on hBN assisted by substrate defects: towards full orientation control Yuanxi Wang, Fu Zhang, Nasim Alem, Vincent Henry Crespi Progress in growing exceptionally high-quality single crystals have long been impeded in polar 2D materials by the ubiquitous presence of inversion domain boundaries caused by what are often near-degenerate 0° and 180° orientations with respect to their substrate. For transition metal dichalcogenides (TMD), it has not yet proven possible to lift this degeneracy, even when grown on lattice-matched polar substrates. We perform a systematic structural search for a TMD/hBN heterostack system using density functional theory and hybrid functional calculations to identify a new mechanism to lift this near-degeneracy: the energetic distinction between eclipsed and staggered configurations during nucleation at a point defect in the substrate. Orientation control is then verified in experiments that achieve ~90% consistency in the orientation of as-grown MoS2 flakes on hBN, as confirmed by aberration-corrected scanning/transmission electron microscopy. [arXiv:1801.00487] |
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T70.00238: Gunther Martin, Maxwell Rabe, Dr. Alem Teklu:
Investigation of the mechanical properties of MOS2 and ReSe2 using an AFM. Gunther Martin We measured the mechanical properties of MOS2 and ReSe2 using an AFM. MOS2 and ReSe2 are promising materials for their flexibility combined with their optical and electronic properties. Values relevant to their commercial use were obtained for Young's Modulus, stiffness, and hardness. |
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T70.00239: Electronic properties, dynamical stability and mechanical properties of zeolite-templated carbon Schwarzites Ross Siegel, Kory Beach, Zachary Ward, Michael C Lucking, Humberto Terrones Periodic crystalline carbon structures, with negative |
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T70.00240: Characterization of 2D Hybrid Systems: Graphene and Beyond Sajedeh Pourianejad, Frederick Aryeetey, ADEYINKA ADESINA, Shyam Aravamudhan, Tetyana Ignatova High-quality junction between semiconductor and metallic contact with no energy barrier is crucial for high-performance device, which is hard to achieve for 2D MoS2 because of its large bandgap. The heterostructure of single-layers MoS2/graphene has been demonstrated. However, a critical challenge has emerged: to develop reliable methods to transfer this graphene from its growth substrate to the application substrate without damaging the fragile patchwork or leaving undesired residues on the graphene surface. To ascertain the MoS2 and graphene layer number and their defects, Confocal Raman spectroscopy and photoluminescence measurements were conducted before and after transfer. To identify the thin film thickness atomic force microscopy (AFM) was performed. Scanning electron microscopy was used to investigate the surface morphologies of MoS2 and Graphene. To confirm the low surface defect results, X-ray Photoelectron Spectroscopy (XPS) was also carried out. We speculate that the tunable Fermi level in graphene allows excellent work-function to be well-matched with MoS2, resulting in low contact resistance. |
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T70.00241: Healing a Topological Scar Benjamin Katz, Vincent Henry Crespi A novel defect type in two-dimensional systems is presented, which changes the local coordination number of an atom in an otherwise regular structure. While point-like by itself, such a 'coordination defect' has an unusually large number of involved atoms and a potentially dramatic influence on the growth of the system following its formation, due to its introduction of a mismatch between bond network topology and physical ring size. The potential growth pathways after the occurrence of such a defect in graphene are followed using molecular dynamics and first-principles calculations; the inherent conflict between the topological requirements and the actual chemical/physical structure that occurs as the system heals the defect can result in varied morphologies, including a runaway feedback that spawns one or more semi-infinite grain boundaries. Energy comparisons from first principles are used to evaluate the likelihood of this result under various conditions. The appearance of this defect type is predicted to have similar ramifications across a broad array of two-dimensional systems, potentially providing a new method of controlling grain boundary behavior and location. |
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T70.00242: Gate-defined Quantum Confinement in few-layer Black Phosphorus Transistor Jiawei Yang, Ruoyu Chen, Shi Che, Kenji Watanabe, Takashi Taniguchi, Seongphill Moon, Dmitry Smirnov, Chun Ning Lau Black phosphorus is a novel two-dimensional(2D) semiconductor which has attracted considerable research interest due to its tunable band gap and high electron mobility. Here we demonstrate quantum confinement defined by split gate in devices based on few-layer black phosphorus. The tunability of split gate can be illustrated by the fact that a device can be tuned off by split gate alone. In quantum Hall regime, gate-controlled pinching off of quantum Hall states(with filling factor ν = -1, -2, -3, -4) indicates the realization of strong confinement and the potential of manipulation of edge states. The work opens the door for using black phosphorus as platform for electronic and optoelectronic applications. |
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T70.00243: Polarized Raman spectroscopy in monolayer ReSe2 Geovani Carvalho de Resende, Bruno R Carvalho, Marcos Pimenta Raman spectroscopy is a powerful tool to study two-dimensional compounds and has been widely used to obtain important information of their electronic and vibrational structures. In the case of graphene and MoS2-type compounds, the Raman spectrum is isotropic when the light polarization lies in the layer plane. However, for low-symmetry materials such as black phosphorus and triclinic transition metal dichalcogenides, the spectra are polarized dependent and polarized Raman spectroscopy should be used. By changing the angle between the light polarization and the crystallographic axes, the elements of the Raman tensors for the different phonon modes can be determined. Previous studies in black phosphorus showed that Raman tensor elements are complex numbers, but the physical origin of the phase differences are not yet well understood. In this work, polarized Raman spectroscopy is used to investigate the anisotropic behavior in monolayer ReSe2. The angular dependence of the polarized Raman spectra using different polarization configurations is obtained for the 18 Raman active modes as well as the Raman tensor elements for each mode. It was also observed that the principal axes of those Raman tensors are not along the crystallographic axes. |
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T70.00244: Magnetoplasmons and magnetoexcitons in doped double-layered $\alpha$-T$_3$ lattice in a strong magnetic field Godfrey Gumbs, Dipendra Dahal, Andrii Iurov, Danhong Huang We investigate the conditions for the occurrence of Bose-Einstein condensation and superfluidity of indirect magnetoexcitons for a pair of quasi-two-dimensional spatially separated $\alpha$-T$_3$ layers. The energy dispersion of collective excitations, the spectrum of sound velocity, and the effective magnetic mass of magnetoexcitons are obtained in the integer quantum-Hall regime for strong magnetic fields. The superfluid density and the temperature of the Kosterlitz-Thouless phase transition are probed as functions of the excitonic density, magnetic field and the interlayer separation. |
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T70.00245: Exciton luminescence efficiency and dynamics in flux-growth MoSe2 monolayers Honghua Fang, Bo Han, Cedric Robert, Delphine Lagarde, Xavier Marie, Bernhard Urbaszek, Takashi Taniguchi, Kenji Watanabe, Sefaattin Tongay Monolayers of transition metal dichalcogenide like MoS2 are promising materials for optoelectronics applications due to their exceptionally strong light-matter interaction governed by very robust excitons (Coulomb bounded electron hole pairs). Nevertheless, practical usage has been hindered by their relatively low quantum efficiency (0.1-1%) due to the presence of non-radiative recombination channels (defects, exciton-exciton annihilation, relaxation to dark states …). In this work, we compare the optical properties of monolayers of MoSe2 exfoliated from different bulk crystals : commercially available crystals from 2D Semiconductors and bulk crystals synthetized with the low temperature flux-growth technique. We perform temperature dependent photoluminescence (PL) and time resolved PL measurements and observe strong differences between the materials in terms of doping level, the PL intensity evolution with temperature and the exciton dynamics at both cryogenic and room temperature. These results are interpreted evoking the lower defect density measured in our flux-growth samples. |
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T70.00246: Diverse Strain Dependent Thermal Transport in 2D Materials Guangzhao Qin, Ming Hu Manipulation of thermal transport is in increasing demand as heat transfer plays a critical role in a wide range of practical applications. While 3D bulk materials usually exhibit decreased lattice thermal conductivity upon mechanical stretching and enhanced thermal transport by compression, the thermal response of 2D materials to mechanical strain is not that simple. Perfectly planar atomically-thin materials such as graphene have reduced thermal transport ability when stretched. In contrast, some 2D materials with intrinsic buckled structure will possess enhanced thermal conductivity upon tension. However, many exceptions exist in other 2D materials. The thermal conductivity of 2D planar group III-nitrides (h-BN, h-AlN, h-GaN) is tremendously enhanced by stretching. By deeply analyzing the orbital projected electronic structure, we establish a microscopic picture of the lone-pair electrons driving strong phonon anharmonicity in group III-nitrides. However, the lone-pair electrons do not necessarily lead to enhanced thermal conductivity in strained penta-like 2D materials. Our findings offer perspectives of modulating thermal transport properties of broad 2D materials for applications such as thermoelectrics, thermal circuits, and nanoelectronics. |
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T70.00247: Band Gaps and Optical Spectra of Fluorinated and Hydrogenated Graphenes Frantisek Karlicky Two-dimensional (2D) materials derived from graphene by attachment of hydrogen and halogens have attracted considerable interest over the past few years because of their potential applications (e.g., in electronic devices or sensing)[1]. Here, we consider the effect of electron-electron and electron-hole correlation on the electronic/optical properties of materials under study. Large difference between the experimental optical gap and the electronic band gap from many-body GW theory for fluorographene CF, fluorographite, and graphane CH is explained by unusual large binding energies of excitons obtained by solution of Bethe-Salpeter equation (BSE}[2,3]. Fluorographane C2FH is found as material with the widest electronic gap (~10 eV) and a largest binding energy of exciton (~3 eV) in the class of currently known 2D materials [4]. Finally, we show the importance of careful computational setup for reliable usage of many-body methods. |
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T70.00248: Impact of structure on exciton physics in organic-inorganic 2D perovskites Jean-Christophe Blancon, Jacky Even, Andreas Stier, Claudine Katan, Jared Crochet, Aditya D. Mohite Organic-inorganic (hybrid) 2D perovskites is a new class of 2D layer materials that feature unique structural characteristics related to their hybrid nature, which includes soft and dynamic lattice structure and organic-inorganic interfaces. There is still little knowledge of the interplay between, on the one hand, their photo-excited states and electronic properties and, on the other hand, their structural characteristics. Here, using optical spectroscopy and 60-Tesla magneto-absorption, we report the dependence of the formation, dynamics, and recombination of exciton states on the structural and compositional details of hybrid 2D perovskites [Nature Communications 9, 2254, 2018 & Science 355, 1288, 2017]. Our work reveals the changes in the exciton properties due to the tuning of the thickness of the 2D perovskites and the size of the organic molecules in the lattice. The exciton characteristics are explained by an advanced model which includes quantum and dielectric confinement. Moreover, we demonstrate the existence of unique electronic states located at the edges of the 2D perovskite layers, which result from local distortions of the lattice at the edges. Finally, we will provide insight into the hetero-coupling between 2D perovskites and transition metal dichalcogenides. |
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T70.00249: Refractory metals as alternate contact metals for 2D/3D Heterostructures Mahesh Neupane, Dmitry A Ruzmetov, Robert A Burke, Matthew L Chin, Mike D Valentin, A. Glen Birdwell, Terrance O'Regan, Tony Ivanov Vertical three-terminal complex devices based on 2D/3D heterostructures require metal contacts that can withstand high temperature and harsh chemical environment brought about by the 2D/3D material synthesis that follows the metal contact fabrication [1, 2, 3]. Refractory metals, such as Mo, W and Cr, are candidates for this purpose and have been used by our team for the fabrication of contacts to the Base (MoS2) in a vertical GaN/MoS2/GaN heterojunction bipolar transistor. Since refractory metals exhibit endurance toward high temperature, abrasion and degradation, they are expected to form sharp, high-quality interface with 2D materials. Motivated by this, we have performed first principle simulation study of refractory metals/2D/3D systems and analyzed structural and electronic properties, such as binding energies, Schottky barrier heights (SBH), and mid-gap charge densities, and investigated the feasibility of using refractory metals as contact metals in 2D/3D systems. Furthermore, we have made an attempt to establish a correlation between the metal type and degree of Fermi level pinning using theoretical as well as in-house experimental data. 1. ACS Nano 10, 3580, 2016, 2. App. Phys. Lett 111, 051602, 2017, 3, 2D Materials 5, 045016, 2018 |
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T70.00250: Electric-field tunable fine-structure splitting in monolayer semiconductors Chitraleema Chakraborty, Nicholas R Jungwirth, Gregory Fuchs, Nick Vamivakas Semiconducting quantum dots (QDs) are among the most promising source of on-demand, indistinguishable single and entangled photon source which are the basic ingredients for quantum communications and computing applications1. The most common approach to generate entangled photon pairs in QDs is to utilize the biexciton to exciton radiative cascade2. Recently, single confined exciton and biexciton emission have been demonstrated at locally strained sites in semiconducting two-dimensional (2D) materials3-5. The 2D host makes them ideal for integrated quantum photonics studies. However, a sizable fine-structure splitting (FSS) (~800 ueV) due to anisotropic electron-hole exchange interaction in these quantum-confined excitons and biexcitons poses a limit to the indistinguishability of the generated photon pairs. We demonstrate a suppression of the FSS by leveraging on van der Waals heterostructure and fabricate a voltage tunable device to minimize the effect of exchange interaction. |
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T70.00251: Spin transistors built on 2D van der Waals heterostructures Shengwei Jiang, Lizhong Li, Zefang Wang, Jie Shan, Kin Fai Mak A transistor based on spin rather than charge (spin transistor) was first proposed by Datta and Das in 1990. Such a spin-based device promises non-volatile data storage and a faster and more energy-efficient performance than present transistors. Many approaches have been pursued to realize spin transistors, but they remain a formidable challenge. Recent discovery of two-dimensional magnetic insulators such as CrI3 with electrically switchable magnetic order and effective spin filtering effect inspires a new operational principle for spin transistors. Here we demonstrate spin field-effect transistors based on dual-gated graphene/CrI3/graphene tunnel junctions. These devices show an ambipolar behavior and tunnel conductance that is dependent on the magnetic order in the CrI3 tunnel barrier. The gate voltage switches the tunnel barrier between an interlayer antiferromagnetic and ferromagnetic state under a constant magnetic bias near the spin-flip transition, thus effectively altering the device between a low and a high conductance state with a large hysteresis. Based on the electrically controlled spin-flip transition in the magnetic tunnel barrier, these new spin transistors achieve spin injection, control and detection in a single device with a conductance ratio approaching 400%. |
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T70.00252: High Photo-response in Conformally Grown Monolayer MoS2 on Rugged Substrate Yong Soo Kim, Tri Nguyen, Tam Chinh Le, Farman Ullah, Kyo-in Koo, Zeeshan Tahir, Eunah Kim, Dongwook Kim, Joon Jang Conformal growth of atomic-thick semiconductor layers on patterned substrates can boost up the performance of electronic and optoelectronic devices remarkably. However, conformal growth is a very challenging technological task, since the control of the growth processes requires utmost precision. Herein, we report on conformal growth and characterization of monolayer MoS2 on planar, micro-rugged, and nano-rugged SiO2/Si substrates via metal-organic chemical vapor deposition. The continuous and conformal nature of monolayer MoS2 on the rugged surface was verified by high-resolution transmission electron microscopy. Strain effects were examined by photoluminescence (PL) and Raman spectroscopy. Interestingly, the photo-responsivity (~254.5 mA/W) of as-grown MoS2 on the nano-rugged substrate was 59 times larger than that of the planar sample (4.3 mA/W) under a small applied bias of 0.1 V. Such enhancement in the photo-responsivity arises from a large active area for light-matter interaction and local strain for PL quenching, where the latter effect is the key factor and unique in the conformally grown monolayer on the nano-rugged surface. |
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T70.00253: Monolithic image sensor and optoelectronics of monolayer. Chen Po-Han, Chang-Ning Liao, Meng-Hsi Chuang, Kuan-Chang Chiu, Meng-Chyi Wu, Chih-Chao Yang, Yi-Hsien Lee Development of advanced optoelectronic devices for ultrahigh speed, low power consumption, and low cost image sensors are emergent applications of Internet of Things (IoT). To achieve ultrasensitive image sensors, high responsivity, fast response speed, and low power consumption are required. Monolayer transition metal dichalcogenides (TMD) crystals are potential candidates for high performance optoelectronic devices with high responsivity and low power consumption. Here, persistent photoconductivity (PPC) of the monolayer TMD are studied and improved. Monolithic image sensor and optoelectronic transport properties of the MoS 2 are demonstrated. |
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T70.00254: Study of graphene/hBN heterostructures using Raman Spectroscopy Jessica Santos Lemos, Leandro Malard Moreira, Daniel Cunha Elias In this work, heterostructures of graphene and hexagonal boron nitride (hBN) were built using the pick-up method and dry-transferred to an insulator substrate (glass). Then, electric contacts were made in order to control the charge carrier concentration applying a voltage between graphene and the golden contact deposited on hBN. In this way, it was possible to access charge concentrations higher than $10^{13}~cm^{-2}$. Aligned sample was desired in order to obtain a Moiré patterning such that the cloning of the Dirac cones would occur for small energy values, being accessible by voltage application. In order to check the formation of the cloning of the Dirac cones due to the Moiré patterning, Raman spectroscopy was used. It was observed a frequency reduction and width increase in the G band for three distinct values of the voltage applied in the sample. The electron-phonon coupling effect was investigated to explain such experimental observations between the different Dirac points and the G band phonons. |
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T70.00255: Few-Layer MoTe2-on-Silicon Laser-like Emitters at O-band Telecom Wavelength Juntao Li, Hanlin Fang, Jin Liu, Thomas F Krauss, yue wang While many essential silicon photonics components have already been demonstrated, silicon light source still cannot be easily incorporated into the silicon devices. The emergence of two-dimensional (2D) transition metal dichalcogenides (TMDs) materials has sparked intense activity in light sources. Although several TMD-based lasers have been demonstrated [1-3], 2D-on-silicon laser at telecom wavelengths is still a challenge. We demonstrate an optically pumped 2D-on-silicon laser-like emitters by employing few-layer TMDs of MoTe2 as a gain material in a silicon photonic crystals cavity at room temperature, with a low threshold power and at O-band telecom wavelengths, which signifies a technological step-change for silicon laser source [4]. The surprising insight is that, few-layer MoTe2 offers a higher overlap between the gain material and the optical mode, resulting a sufficient gain at 1300 nm for fiber coupling output. This opens a new opportunitie for deploying manufacturing methods like chemical vapor deposition and thereby brings 2D-on-silicon laser a step closer for silicon photonics. |
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T70.00256: Photodetector detecting specific range of visible light in vertically-stacked graphene/hBN/metal Jun-Ho Lee, Tae Young Jeong, Younggyu You, Do-Hyun Park, Han Byeol Lee, Inchul Choi, Nae bong Jeong, Young Jin Cho, You Shin No, Hyun-Jong Chung Many people have researched photodetectors made with 2D materials due to its attractive properties such as flexibility and high mobility. the 2D semiconductor is very useful to detect a full range of visible light because of its band gap which is estimated to be 1.9 eV. But it is very difficult to detect specific range of visible light. Because this photodetector converts light photons into current depending on its band gap, and the band gap can be changed only by a type and thickness of 2D material. |
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T70.00257: Aharonov Bohm effect in bilayer graphene Fanrong Lin, Hao Chen, Jens Martin Dual-gated bilayer graphene is an ideal platform to study Aharonov Bohm effect with the ability to tune carrier density and electric field independently. We have fabricated ring-shaped devices and disc-shaped devices as control, with BN-encapsulated bilayer graphene and graphitic bottom and top gates. In our high quality bilayer graphene the quasi-ballistic nature of electron transport at low temperature enables us to study phase-coherent electron transport. We detect Aharonov Bohm oscillations in the ring-shaped devices where the visibility of conductance oscillations reaches 2% at high charge carrier density and temperature of 1.4K. Meanwhile, we also explore magneto-transport properties of valley currents near zero carrier density and in the presence of an external electric field. The nonlocal valley-signal shows strong magnetic field dependence. We will discuss possible mechanisms. |
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T70.00258: Electrical properties of graphene field-effect transistors functionalized with aryldiazonium salts Anouk Béraud, Amira Bencherif, Claudia Marcela Bazan, Delphine Bouilly Functionalization of graphene field-effect transistors (G-FETs) is necessary to ensure specificity in sensor applications. Among functionalization strategies, aryldiazonium salts are often chosen to form stable covalent adducts. Here we analyze the effect of this chemistry on the electrical properties of graphene field-effect transistors. First, we conducted an extensive review of published experiments and developed a theoretical framework to compare data obtained indifferent conditions (channel size, reagent concentration, incubation time). From the aggregated dataset, we found that the electronegativity of the para group seems to have little impact on the electrical response, which contrasts with conclusions found in the literature. We also found that the type of graphene (exfoliated, CVD, RGO) seems to have a much more dominant impact, which could explain strong differences between previous studies. Finally, we argue that device-to-device variations are significant, and we propose an experimental design based on multiple GFETs arrays and statistical analysis to unambiguously characterize the effect of aryldiazonium functionalization on graphene transport properties. |
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T70.00259: Graphene-based catalytic mats for Belousov Zhabotinsky reaction D Jaya Prasanna Kumar, Sachin Verma, Kabeer Jasuja, Pratyush Dayal Use of hybrid materials that have morphological features at various length scales has opened up new avenues to design multi-functional materials. Here, we synthesize graphene-based catalytic mats and harness their unique properties to tune the kinetics of self-oscillating BZ reactions. In particular, we create catalytic mats containing 0D-2D heterostructures by decorating Ce, Ru, Ag, and Au nanoparticles (NPs) onto the graphene sheet and subsequently, use these nanocomposites to catalyze the BZ reaction. The NPs attached on the graphene function as spacers by increasing the interlayer distance to several nanometers and thus, prevent the stacking of individual graphene sheets. Moreover, the presence of NPs on highly conductive graphene sheets provides enhanced access to active catalytic sites and reveals a multi-fold increase in the number of chemical oscillations frequency in BZ reactions. We also validate the kinetic model of the BZ reaction with our experimental results and identify key parameters to model the reaction kinetics for our BZ system. We expect that our findings will offer a novel approach to design synthetic smart materials with tunable dynamic behavior. |
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T70.00260: Nanoelectromechanical resonators from thin superconducting crystals of BSCCO SUDHIR SAHU, Jay Kumar Vaidya, Digambar Jangade, Arumugam Thamizhavel, Mandar Deshmukh, Vibhor Singh High transition-temperature superconductors host a rich variety of quantum phases. Cavity optomechanics techniques could be helpful in a sensitive detection of long-wavelength phonon modes carrying imprints of the electronic phases. Here we present mechanical resonators fabricated with thin exfoliated crystals of BSCCO at low temperatures. For mechanical readout, we couple their motion to a coplanar waveguide microwave cavity fabricated with a superconducting alloy of molybdenum-rhenium. We perform spectroscopic and time-domain measurements to understand dissipation in these systems. Our results suggest that the performance of these devices is limited by the contact resistance arising from the insulating outer layer, and interlayer friction. |
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T70.00261: Superconductivity from Valley Fluctuations and Approximate SO(4) Symmetry in a Weak Coupling Theory of Twisted Bilayer Graphene Yizhuang You, Ashvin Vishwanath We develop a weak coupling approach to superconductivity in twisted bilayer graphene, starting from the Fermi liquid regime. A key observation is that near half filling, the fermiology consists of well nested Fermi pockets derived from opposite valleys, leading to enhanced valley fluctuation, which in turn can mediate superconductivity. This scenario is studied within the random phase approximation. We find that inter-valley electron pairing with either chiral (d+id mixed with p-ip) or helical form factor is the dominant instability. An approximate SO(4) spin-valley symmetry implies a near degeneracy of spin-singlet and triplet pairing. On increasing interactions, commensurate inter-valley coherence wave (IVCW) order can arise, with simultaneous condensation at the three “M” points in the Brillouin Zone, and a 2 × 2 pattern in real space. In simple treatments though, this leads to a full gap at fillings ±(1/2 + 1/8), slightly away from half-filling. The selection of spin-singlet or spin triplet orders, both for the IVCW and the superconductor, arise from SO(4) symmetry breaking terms. Mott insulators derived from phase fluctuating superconductors are also discussed, which exhibit both symmetry protected and intrinsic topological orders. |
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T70.00262: Realizing Td phase at room temperature in ultrathin MoTe2 Gaihua Ye, Zhipeng Ye, Rui He, logan winford, Shazhou Zhong, Hyun Ho Kim, Adam Tsen MoTe2 emerges as a new type of transition metal dichalcogenide (TMD) whose differnet polymorphs show very different properties. In bulk MoTe, both hexagonal 2H phase (semiconducting) and monmclinic 1T' phase (semimetallic) can be formed at room temperature depending on the growth conditions. When temperature is lowered to 250K, the 1T' phase transforms into an orthorhombic Td phase in which the MoTe2 crystal is a type-II Weyl semimetal with novel quantum phenomena. We exfoliated 1T'-MoTe2 flakes on SiO2 substrates and protected them with boron nitride from oxidation. Electrical transport measurements show that the ultrathin flakes do not show a phase transition below 250K. Raman studies reveal that the MoTe2 ultrathin flakes exhibit a Td phase even at room temperature, making it a potential host material for realizing type-II Weyl semimetal at room temperature. |
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T70.00263: The weight of the Berry Curvature Dipole Oles Matsyshyn, Snehasish Nandy, Inti Sodemann Two independent recent experiments have reported the discovery of the non-linear Hall effect in transition metal dichalcogenides ( arXiv:1809.08744 (2018) and arXiv:1809.09279 (2018)). Within a simple semiclassical model, such non-linear Hall response is controlled by the Berry curvature dipole, which is defined as the average of the gradient of the Berry curvature over the occupied states. In this work we investigate certain deeper microscopic underpinnings of the Berry curvature dipole. We will argue that the Berry dipole plays a role analogous to the Drude weight in the case of non-linear response and quantifies an acceleration of the electron liquid which is second order in electric fields. We will describe new sum rules for the second order electrical response in metals that involve the Berry dipole. We also investigate the role of disorder and show that there are non-linear counterparts to the side-jump corrections with the same scaling with the scattering rate as the Berry dipole contribution which will important when analyzing experiments. |
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T70.00264: Evidence for a phononic origin of the charge density waves in 2H-TaS2 and other transition metal dichalcogenides Kapila Wijayaratne, Junjing Zhao, Christos Malliakas, Duck Young Chung, Mercouri Kanatzidis, Utpal Chatterjee The underlying mechanism of charge density waves (CDW) is still an unresolved problem, both in general and in the specific scope of transition metal dichalcogenides (TMD). Here we report an Angle-Resolved Photoemission Spectroscopy (ARPES) study of the incommensurate CDW order in the 2H (trigonal prismatic) polytype of TaS2. In this prototype two-dimensional system, we observed pronounced temperature independent, yet moment dependent many-body renormalizations of the electronic band dispersion. Detailed analysis revealed that these signatures can be related to phonon modes. Similar observations reported for TaSe2 and NbSe2 suggests this phononic origin can be a general phenomenon for TMDs. Furthermore, the persistence of these renormalizations was observed above CDW transition temperature corroborating pre-reported pseudogap effect. Also, the introduction of strong electron-phonon interactions to a tight binding model led to a successful explanation of a multitude of behaviors generally exhibited by CDW s in TMDs as well. |
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T70.00265: Accelerated design of Fe-based soft magnetic materials using machine learning and stochastic optimization Yefan Tian, Yuhao Wang, Joseph Hansbro Ross, Raymundo Arróyave To significantly expedite the material discovery and design process, we demonstrated a machine learning study of the Fe-based soft magnetic materials database composed of published experimental results, which can be used to efficiently understand and optimize different properties of soft magnetic materials, thus accelerating the design process of next-generation soft magnetic nanocrystalline materials. Various soft magnetic properties, including magnetic saturation, coercivity, and magnetostriction, were studied by different machine learning approaches. Machine learning regression models were trained to predict soft magnetic properties, where random forest shows the best performance. Stochastic optimization was then used to discover new material chemical compositions and secondary processing conditions in order to optimize corresponding properties based on different applications. |
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T70.00266: Electronic properties of bare and functionalized 1- and 2-Dimensional Tellurene structures Daniel Wines, Fatih Ersan, Jaron Kropp, Gracie M Chaney, Can Ataca Recently, 1D and 2D Tellurene structures have been experimentally synthesized. These structures possess high mobility and air stability which make them ideal candidates for applications in electronics, optoelectronics and energy devices. We performed density functional theory and molecular dynamics simulations to investigate the stability and electronic structure of 1D α, β and Γ Tellurene chains, 2D α and β Tellurene sheets, and hydrogen, oxygen, and fluorine functionalized counterparts, including spin-orbit coupling effects. Our calculations show that bare α and β Tellurene sheets are stable and have direct band gaps of 0.56 eV and 1.02 eV respectively. When hydrogenated, α-Tellurene displays metallic properties while the direct band gap of β-Tellurene increases to 1.72 eV. Our calculations also show that α and β Tellurene chains are unstable while Γ Tellurene chains are stable. Our molecular dynamics calculations indicate that Γ Tellurene chains gain kinetic energy and rotate around the chain growth direction. This rotation provides stability to the Γ Tellurene chains. Our results indicate that functionalized-Tellurene chains and monolayers are not only suitable for future optoelectronic devices, but they can be used as metallic contacts in nanoscale junctions. |
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T70.00267: Interaction of the system titanium-borophene with lead substrate with water molecule. Gregorio Ruiz-Chavarria In this work I made an computational study of the interaction of the system titanium-borophene with lead substrate with water. I first established the stability of the borophene system with lead substrate, then added titanium, studying the stability of this system, which was stable. Finally, an water molecule is added, studying the evolution of the interaction between this molecule and the system titanium-borophene with lead substrate. To do this work, I use Density Functional Theory, Born-Oppenheimer Aproximation, atomic pseudopotentials and molecular dynamics. The results obtained are compared with experimental results, as well as with similar calculations. |
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T70.00268: Critical electronic and many-body properties of α-T3 nanoribbons Paula Fekete, Andrii Iurov, Godfrey Gumbs, Danhong Huang Quasi-one-dimensional nanoribbons of finite width could be produced from the recently proposed α-T3 materials with variable hub-rim coupling parameter similarly to nanoribbons fabricated from graphene. We investigate their critical electronic and collective properties, such as plasmons, based on the tight-binding model for the low-lying energy bands and spin-1 Dirac-Weyl equation with the proper boundary conditions. Our results strongly depend on the type of boundary which our nanoribbon has. We believe that the novel electronic properties we obtained will significantly benefit the field of currently existing carbon-based nanoelectronics and nanodevices. |
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T70.00269: A First-Principles Investigation of Spintronic Capabilities of Nitrophosphorene Doped
With 3d Transition Metals Lawrence Shi, Xuan Luo There has been search for materials with spintronics properties as they have potential advantages in data transfer and storage over their conventional electronics counterparts. Notably, phosphorene is at the center of such material search with its widely tunable band gap and high carrier mobility. Nitrophosphorene (PN), a newly discovered material in 2017, is considered to be a superior semiconductor to Black Phosphorene (BP) because of its larger band gap. However, unlike BP, whose spintronic properties have been well studied, little is known about the spintronic properties of PN. We present strong evidence that PN is potentially an even better material for spintronics than BP. Specifically, we used first-principles calculations to investigate the spintronic properties of 3d transition metal-doped PN. Sc, Cr, and Co doping result in a DMS. V, Mn, and Fe doping result in a half metal, and Ti and Ni doping result in a semiconductor with no magnetization. We also compared the spintronic properties of interstitial Mn-doped PN and interstitial Mn-doped BP. Although both of them are half-metals, Mn-doped PN has a higher magnetization and band gap. Our discovery in PN spintronics contributes to the recent advances in the fundamental studies and search for spintronics materials. |
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T70.00270: Predicting Synthesizable Functional Edge Reconstructions in 2D Monolayers Guoxiang Hu, Xiahan Sang, Raymond Unocic, Panchapakesan Ganesh Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted tremendous interest due to their exceptional electronic and optical properties. More interestingly, it has been found that edges of 2D TMDCs are responsible for their promising catalytic activity, while the basal plane is chemically inert. In addition to the conventional armchair and zigzag edges, more complex edge reconstructions have recently been realized by various experiments. Therefore, it is highly desirable to computationally predict the family of stable edges so as to screen their functional properties. Here we report development of such a computational approach and demonstrate it on the 2D TMDC family of systems such as MoS2 & MoSe2. Starting from configuration ensemble generations, we screen for stable edges using cheaper force-fields or surrogate (Neural-Network-based) models, which are then further refined using DFT-level of theory. We predict many stable edges that are superior for hydrogen evolution reaction (HER). Our study thus provides a comprehensive yet tractable computational approach for predicting synthesizable functional edges in 2D monolayers. |
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T70.00271: JARVIS: Novel NIST databases to aid Material Discovery Kamal Choudhary
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T70.00272: The glassy solid as an ensemble of crystalline microstates Eric Jones, Vladan Stevanović While theoretical modeling of the atomic scale structure of non-crystalline solids has become well developed, deriving functional properties from these models still faces challenges. In order to address this deficit, we analytically demonstrate a decomposition of the non-equilibrium glassy macrostate into a statistical ensemble of crystalline microstates with an effective temperature. Crystalline microstates are calculated as local potential energy minima using density functional theory. With the radial distribution function and powder diffraction intensity as signatures of short- and long-range order respectively, we show that the glassy states of both silicon and silica can be reproduced with remarkable fidelity using crystalline microstates with unit cells on the order of just a few dozen atoms. Our approach offers a complementary view to the conventional supercell-based continuous random network model, which typically singles out a single representative microstate for the purposes of modeling. By contrast, our model presents the glassy state as an effective liquid, which visits crystalline potential energy minima ergodically, opening the door to new predictive methods for property calculations based on ensemble averaging and to the rational design of glassy solids. |
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T70.00273: MSCD Framework
A Novel Computational Design Software for High-Temperature Superconductors Onyedinachi Ironkwe Computational materials design of high Tc superconductors is an emerging field with few reported successes. Present approaches utilize DFT, DMFT and machine language data-mining techniques. We have developed a new approach, strongly based on Periodic Table correlations of high temperature superconductors. This new design model treats superconductors as “superatoms” hence “layered elements”. It utilizes parameters such as electronegativity, valence electrons, atomic number, valence state, layers, and ionic radii and relates them to the superconducting state and the periodicity of the elements. We will present the details of this novel powerful software with predictive power for designing HTSCs and their transition temperatures, Tc, without too much computation. |
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T70.00274: Arc Synthesis of Boron Nitride Nanotubes Alexander Khrabryi, Yevgeny Raitses, Shurik Yatom, Igor Kaganovich We present recent results on stable and reliable synthesis of boron nitride nanotubes (BNNTs) in volume by an anodic arc discharge at near atmospheric pressure of nitrogen. This arc was operated with the boron-rich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. Ex situ anlysis results also show evidence of root-growth of BNNTs produced in the arc discharge. In order to understand nanostructure formation we needed to determine the plasma and gas composition conditions in the nucleation and growth region. We determined plasma parameters in the growth region using plasma diagnostics and thermodynamic modelling. Previous atomistic simulations helped to analyse crucial processes in nanomaterial synthesis. References are available at nano.pppl.gov |
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T70.00275: Towards Understanding of Arc-Based Synthesis of Carbon Nanotubes Yevgeny Raitses, Shurik Yatom, Alexander Khrabryi, Vlad Vekselman, Igor Kaganovich This work reports on studies of arc-based synthesis of carbon nanomaterials. Applying a set of the in-situ diagnostics of plasma and nanoparticles, our synthesis experiments revealed that the carbon arc forms a highly inhomogeneous plasma consisting of distinguishable regions with different dominant species, including ions, atoms, molecules and clusters, and nanoparticles. Measurements revealed clouds of nanoparticles in the arc periphery bordering the region with a high density of diatomic carbon molecules. Two-dimensional CFD simulations of the arc combined with thermodynamic modeling show that this is due to the interplay of the condensation of carbon molecular species and the convection flow pattern. The formation of nanoparticles is strongly affected by unstable arc behavior. |
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T70.00276: Multilayer graphene shows intrinsic resistance peaks in the carrier density dependence: experiments in tetra- and hexlayer graphene Ryuta Yagi, Taiki Hirahara, Ryoya Ebisuoka, Takushi Oka, Shingo Tajima, Kenji Watanabe, Takashi Taniguchi Since the advent of graphene, a variety of studies have been done to elucidate its fundamental physics, or to explore its practical applications. Gate-tunable resistance is one of the most important properties of graphene and has been studied in 1-3 layer graphene in a number of efforts to control the band gap to obtain a large on-off ratio. On the other hand, the transport property of multilayer graphene with more than three layers is less well understood. Here we show a new aspect of multilayer graphene. We found that four-layer shows intrinsic peak structures in the gate voltage dependence of its resistance at zero magnetic field. Measurement of quantum oscillations in magnetic field confirmed that the peaks originate from the specific band structure of graphene and appear at the carrier density for the bottoms of conduction bands and valence bands. Similar but different peak structures were observed in six-layer graphene. The intrinsic peak structures should generally be observed in AB-stacked multilayer graphene. The present results would be significant for understanding the physics of graphene and making graphene FET devices. ( Sci. Rep. 8, 13992 (2018). DOI: 10.1038/s41598-018-32214-7) |
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T70.00277: Controlling graphene structures and electronic properties by Ion beam irradiation Kosuke Nakamura, Kazuyuki Takai, Tomoaki Nishimura, Hiroki Yoshimoto Irradiation of ion into graphene is interesting in view of defect-introduction and chemical modification. In this study, we attempted 200 keV Au or I ion injection to graphene. Irradiation to bear graphene will cause damage, so a sacrificial layer protecting graphene was designed and fabricated on the surface. NaCl thin-film was applied for sacrificial layer, where it has been confirmed NaCl hardly affects structural and electronic properties of graphene after removal process. Raman spectroscopy of Au or I ion irradiated graphene by using NaCl thin-film as a sacrificial layer, shows peculiar G band intensity of graphene near 1580 cm-1, indicating honeycomb structure of graphene was preserved after irradiation . Also defects that cause significant intervalley scattering (D band : 1340 cm-1) and intravalley scattering (D’ band : 1620 cm-1) appeared after irradiation. Field effect transistor (FET) of graphene was fabricated after irradiation, and the mobility of irradiated graphene was measured by applying gate voltage sweep range. The mobility of Au and I irradiated graphene decreased down to 0.114 cm2 / Vs and 0.034 cm2 / Vs respectively, being responsible for extremely less conductivity. |
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T70.00278: Hydrogen adsorption on atomic vacancies in Epitaxial graphene toward Hydrogen storage Yoshinori Obata, Koichi Kusakabe, Gagus Ketut Sunnardianto, Toshiaki Enoki, Isao Maruyama, Tomoaki Nishimura, Kazuyuki Takai Defects introduction is one of the important strategy to tune graphene properties. Especially, it is known that an ion beam irradiation can introduce atomic vacancies in graphene. Although, the number of defects is usually focused, the chemical structure of defects has been not well considered. Actually, for hydrogenated atomic vacancies, the theoretical calculation shows a low energy barrier and little adsorption heat for the additional adsorption of hydrogen molecules, suggesting an efficient hydrogen storage and release in this system. In this study, hydrogenated / oxygen-terminated atomic vacancies are introduced into epitaxial graphene and the amount of hydrogen and carrier scattering related to vacancies are evaluated. Hydrogenated and oxygen-terminated atomic vacancies were introduced into epitaxial graphene by ion beam sputtering, followed by exposing to H2 gas and air, respectively. After introducing hydrogenated vacancies, the increment of hydrogen is comparable to the upper limit for the number of vacancies. The smaller Raman D-band for hydrogenated vacancies than that for oxygen terminated vacancies suggests the inter valley scattering depends on the chemical structure of defects in graphene. |
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T70.00279: Cleaving colloidal chains by photoinduced electron transfer on the particle surface Guruswamy Kumaraswamy, Saurabh Usgaonkar, Subrajeet Deshmukh, Bipul Biswas, Jayaraj Nithyanandhan, Aakash Sharma Fluorescent silica or polystyrene latex particles are commercially available and are widely used in soft matter research. Recently, we demonstrated the preparation of chains of fluorescent colloids held together by a crosslinked mesh of an amine containing polymer, polyethyeneimine (Faraday Discussions, 2016, 186, 61; ACS Nano, 2017, 11, 10025). However, on prolonged excitation of the fluorescent dye, the collaidal chains were cleaved. Here, we demonstrate that free radical reactions can be initiated by irradiation of fluorescent colloidal particles adsorbed with PEI. Free radical ions generated at the surface can cleave a cross-linked polymer mesh that holds together colloidal assemblies or can polymerize acrylic acid monomer at the particle surface (viz. bond breaking or bond formation). Proximity of polymeric amine groups allows photo-induced electron transfer from excited dye molecules, to form free radical ions. Formation of free radical ions is not a function of the size of the colloid, neither is it restricted to a specific fluorophore. Fluorophores with redox potentials that allow photo-induced electron transfer with amine groups show formation of free radical ions. |
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T70.00280: Low-energy band structure and even-odd layer number effect in AB-stacked multilayer graphene: evolution of Landau fan diagrams from 1 to 7 layers Ryuta Yagi, Taiki Hirahara, Ryoya Ebisuoka, Tomoaki Nakasuga, Shingo Tajima, Kenji Watanabe, Takashi Taniguchi How atoms acquire three-dimensional bulk character is one of the fundamental questions in materials science. Before addressing this question, how atomic layers become a bulk crystal might give a hint to the answer. While atomically thin films have been studied in a limited range of materials, a recent discovery showing how to mechanically exfoliate bulk crystals has opened up the field to study the atomic layers of various materials. Here, we show systematic variation in the band structure of high mobility graphene with one to seven layers by measuring the quantum oscillation of magnetoresistance. The Landau fan diagram showed distinct structures that reflected differences in the band structure, as if they were finger prints of multilayer graphene. In particular, an even-odd layer number effect was clearly observed, with the number of bands increasing by one for every two layers and a Dirac cone observed only for an odd number of layers. The electronic structure is significantly influenced by the potential energy arising from carrier screening associated with a gate electric field. (Sci. Rep. 8, 13018 (2018). DOI:10.1038/s41598-018-31291-y) |
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T70.00281: Magnetic Proximity Effect in Graphene/BiFeO3 Hybrid System Hua-Ding Song, Zhi-Min Liao, Dapeng Yu Graphene, a very intriguing 2D massless fermionic system with high carrier mobility, is promising for spintronics. However, the spin splitting is always weak in pristine graphene. Here, we report the transport properties of graphene coupled to an antiferromagnetic insulator BiFeO3. It is found that the magnetic proximity effect results in a strong Zeeman splitting in graphene with the obvious spin splitting in Landau levels. ν=0 quantum Hall state of the coupled system undergoes quantum phase transitions as a result of the combined effect of exchange field and external field. The direction of the external magnetic field also shows its capability to adjust the proximity effect at the interface, by tuning the interfacial magnetization. We also achieve the electrical control of the magnetic proximity effect via strong magneto-electric coupling in BiFeO3 nanoplates. Our findings in graphene/BiFeO3 heterostructure are therefore promising for future spintronics. |
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T70.00282: Thermal Conductivity of Pure and Doped Graphene Girija Dubey, Sarita Mann, Vassilios Fessatidis, Hitesh Sharma, Godfrey Gumbs, Vijay Jindal In this work we have studied the thermal conductivity of both pure graphene and boron-doped graphene structure. The calculations have been performed using ab-initio density functional perturbation theory, implemented in VASP software, to study structural properties and calculated the interatomic forces/force constants of pristine/doped graphene. Thermal conductivities are calculated by solving linearized Boltzmann transport equations (LBTE) using single mode relaxation time approximation (RTA). The phonon density of states and thermal conductivity were calculated using phonopy and phono3py. A graphene sheet of 32 atoms was considered for calculating second order force constants while an 8 atom sheet was used to calculate third order force constants. A smaller sheet was used for third order force constant calculation as it requires high computation. Doping concentrations of 12.5% and 25% B dopants were used in this work since higher concentration of dopants lead to unstable structures. |
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T70.00283: Infrared Spectroscopy of Dual-Gated Bilayer Graphene Jordan Russell, Jordan Pack, Yashika Kapoor, Takashi Taniguchi, Kenji Watanabe, Erik Henriksen We have performed infrared transmission spectroscopy measurements on dual-gated encapsulated bilayer graphene. In these measurements, we have observed intra- and inter-band resonances of bilayer graphene which we study as a function of magnetic field, filling factor, and displacement field. We will share comparisons between measurements of devices with metal and graphite gates. Methods of distinguishing sample resonances from resonances observed in the silicon and graphite gates will also be discussed. |
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T70.00284: Energy Relaxation of Hot Dirac Carriers in CVD Graphene-based Heterostructures Jinggao Sui, Jack Alexander-Webber, Ye Fan, Hiromu Gamou, S Hofmann, Malcolm Connolly, Charles G Smith The two dimensional character of graphene makes it a promising material to be used in the post-silicon electronics era. Despite the exceptional electronic properties, the lack of a bandgap in monolayer graphene limits its potential applications. The creation of heterostructures based on graphene and other two-dimensional crystals can help overcome some limitations. We present a fabrication process and magnetotransport measurements to study the hot carrier dynamics in scalable bilayer CVD graphene and graphene-on-WSe2 heterostructures. Energy relaxation of hot Dirac fermions in these systems is experimentally investigated by Shubnikov–de Haas oscillations and weak localization[1]. Energy loss rates in graphene-based heterostructures have been found to follow the predicted Bloch–Grüneisen power-law behaviour. The electron-phonon relaxation time has also been observed to be carrier density dependent. Hot carrier dynamics in graphene has considerable importance in determining the performance of high frequency and high power electronics, high-speed sensors and quantum Hall metrology for accurate measurements[2]. |
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T70.00285: Electronic transport in graphene decorated with Bi2Te3 nanoparticles Joshua Cohen, Jamie Elias, Takashi Taniguchi, Kenji Watanabe, Fudong Wang, William Buhro, Arashdeep S Thind, Rohan Mishra, Erik Henriksen
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T70.00286: STATISTICAL THERMODYNAMICS OF DICE LATTICE CARRIERS Norman J.M. Horing, M Lawrence Glasser, Jay D Mancini We have developed the retarded and thermodynamic Greene’s functions for Dice Lattice carriers and employed them in the determination of the Dice Lattice statistical thermodynamic functions, including the Helmholtz Free Energy, grand partition function, ordinary partition function, and entropy. These evaluations are carried out for arbitrary temperature and chemical potential, including the degenerate and nondegenerate statistical regimes. |
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T70.00287: Are freestanding Xene monolayers excitonic insulators in their ground state? Matthew Brunetti, Oleg Berman, Roman Kezerashvili We present evidence that monolayers of Xenes (silicene, germanene and stanene) suspended in vacuum behave as excitonic insulators in their ground state, by drawing upon well-established ab initio and theoretical models of the electronic structure of these materials. By solving the Schrödinger equation for electrons and holes interacting via the Rytova-Keldysh potential, it is shown that the direct exciton binding energy exceeds the band gap when the external electric field is small or zero [1]. We propose a phase transition in freestanding monolayer Xenes from the semiconducting phase to the excitonic insulating (EI) phase can be induced by reducing an external electric field below some critical value which is unique to each material. Our calculations show the coexistence of the semiconducting phase of A excitons with the EI phase of B excitons for a particular range of electric field. Enhanced dielectric screening in supported or encapsulated monolayer Xenes precludes the existence of the EI phase in those scenarios. |
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T70.00288: Mechanical and electronic properties of 2D green phosphorene, a first-principles study Guang Yang, Tianxing Ma, Xihong Peng Recently, a phosphorus isomer named green phosphorus was theoretically predicted with a similar interlayer interaction compared to that of black phosphorus, thus indicating that individual layers can be mechanically exfoliated to form two-dimensional (2D) layers known as green phosphorene. The 2D structure shows high stability and was predicted to have a direct band gap up to 2.4 eV. First-principles density functional theory calculations were used to investigate the mechanical properties and strain effect on electronic band structure of the 2D green phosphorene along two perpendicular in-plane directions. Remarkably, it was found that the material can sustain a tensile strain in the armchair direction up to a threshold of 35% which is larger than that of black phosphorene, suggesting that green phosphorene has more puckered structure. The results also showed that the Young’s modulus and Poisson’s ratio in the zigzag direction are four times larger than those in the armchair direction, which confirms the anisotropy of the material. Furthermore, uniaxial strain can trigger the direct-indirect bandgap transition in the material, and the critical strains for the bandgap transition are revealed. |
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T70.00289: Van-der-Waals-gap tunneling spectroscopy for low dimensional materials DONG HWAN CHOI, Ju-Jin Kim, Myung-Ho Bae, Kyung-Ah Min, Suk-Lyun Hong Field-effect transistors based on low-dimensional materials such as carbon nanotubes (CNTs), graphene, and transition metal dichalcogenides have been developed in order to provide enhanced electronic performance, with significant efforts to overcome the van der Waals (vdW) gap between the metal and inert material components. We report a new method that offers a high resolution tunneling spectroscopy by adopting tunnel barrier as the vdW interface indium (In) metal and low-dimensional nano-structures without an artificial insulating tunnel barrier. We show that multiple differential conductance peaks for varying bias voltages correspond to the van Hove singularities existing in the electronic density of states of CNTs. For the multi-layer MoS2 FET, conductance shoulders were observed at the source-drain voltage (Vsd) of ~0.9 V and were attributed to a semiconducting gap. For the 1T-TaS2 case, Mott-gap induced conductance peaks at Vsd ~ 0.2 V were observed at T = 4 K, which coexist with the commensurate charge-density-wave phase. |
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T70.00290: Temperature-dependent optical and transport conductivities in doped silicene Andrii Iurov, Godfrey Gumbs, Danhong Huang We examined the thermal transport properties of silicene, germanene and other buckled honeycomb lattices with finite electron doping. Both Boltzmann and optical conductivities are computed based on the finite-temperature polarization function, Such thermally convoluted polarizability is calculated using temperature-dependent chemical potentials. We have analyzed the frequency dependence of both real and imaginary parts of the optical conductivity. Specific features of the obtained spectral dependence can be used for analyzing plasmon damping in silicene and ultrafast light modulations. We also calculated transport conductivities for various doping concentrations and band gaps using the second-order Born |
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T70.00291: Low-energy bandstructure, electronic states and Berry phases in α-T3 materials under external
irradiation Liubov Zhemchuzhna, Andrii Iurov, Godfrey Gumbs, Danhong Huang Electron dressed states, or interacting Floquet states, have been derived analytically for α-T3 materials. These arise from the off-resonant coupling of Dirac pseudospin-1 electrons to the external irradiation. Results will be presented over the allowable range of values of the interaction parameter α 0 < α < 1 and for all possible types of incoming light polarizations. For elliptical and circular polarizations, an energy band gap could be opened, there is no longer symmetry between the valence and conduction bands, and the obtained low-energy bandstructure directly depends on the valley index τ . In contrast, applying linearly polarized light could induce α-dependent anisotropy of the dispersions, but there is no change to the flat band. We have obtained and examined the corresponding wave functions, their structure and Berry phases. |
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T70.00292: Exploration of exciton behavior in atomically thin WS2 layers by ionic gating Xin He, Zehui Zhang, Chenhui Zhang, Yang Yang, Ming Hu, Weikun Ge, Xixiang Zhang The photoluminescence spectra of mono- and bilayer WS2, gated by the ionic liquid, were systematically studied at 77 K. Interesting phenomena, such as a redshift of the exciton peaks and a change in the spectral weight of the exciton, trion, and biexciton peaks, were observed at intermediate doping levels. By increasing the doping level, all the exciton, trion, and biexciton peaks vanished, which is attributed to the phase-space filling effect and the Coulomb screening effect. The variation in the band structure, which was induced by the quantum-confined Stark effect in both the mono- and bilayer WS2, was also studied using first-principle calculations. |
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T70.00293: The control of the double-slit silicene interferometer by the spin-Hall effect Bartlomiej Rzeszotarski, Bartlomiej Szafran Silicene [1] is a novel 2D-material similar to the graphene with buckled structure that provides spin-orbit coupling (SOC) which is a source of topological physics. In silicene zigzag nanoribbons for low Fermi energy the quantum spin Hall effect [2] occurs and the charge currents for both spin orientation flow along opposite edges of the ribbon. Here, we present an idea for the double-slit-interference device with one input lead that splits to double channels (Y-shape) based on the atomistic tight-binding approach [3]. The double channel is connected to an unconfined silicene half-plane with a third lead used as a detector. The double-slit interference can be detected with the external magnetic field that triggers the Aharonov-Bohm conductance oscillations only when the electron wave functions passes through both the arms of the split input channel. The Aharonov-Bohm oscillations are attenuated when the system is driven in the quantum spin Hall regime, when the wave functions passing through both the channels have opposite spins. |
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T70.00294: Polarization charge coupling effect in 2D van der Waals-ferroelectric heterostructure Hye-Jin Jin, Jayeong Kim, Yejin Kim, Seokhyun Yoon, Yangjin Lee, Kwanpyo Kim, William Jo In two-dimensional (2D) layered semiconducting materials, charge distribution is controlled by ferroelectric polarization and inequivalent charge distribution is obtained vertically. Ferroelectric polarization induced accumulation or depletion in 2D semiconductors resulting in polarization charge coupling effect. In this study, 2D semiconductors (n-type MoS2 and p-type WSe2) and ferroelectric PbTiO3 (PTO) thin films were integrated vertically. We used conductive atomic force microscopy to study vertical transport and light illumination effect is also studied. Enhanced resistive switching effect was obtained and polarization was exploited to control resistive switching characteristics. In addition, charge separation is effectively obtained due to built-in interfacial electrical field at interface between 2D semiconductor and PTO thin films. In particular, photovoltaic response is obtained in the heterostructure and polarization can behave as a physically-doped electrode. Polarization gives stable and additional separation of electron-hole pairs in 2D semiconductors and increase of photoresponse is obtained. Therefore, we can expect application for a photo-memristor and suggest new memory and photovoltaic devices by integrating 2D semiconductors and ferroelectrics. |
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T70.00295: Tunnelling spectroscopy of localized states in WS2 based van der Waals heterostructures Niks Papadopoulos, Pascal Gehring, Takashi Taniguchi, Kenji Watanabe, Herre S.J. van der Zant, Gary Steele Defects in semiconductors and dielectrics can provide rich physics with technological potential such as quantum photon emission, spin control and they might be potential platforms for realizing quantum entanglement. In transition metal dichalcogenides, defects have been found to play important role as they affect the doping and the spin-valley relaxation dynamics. Herein we study localized states in WS2 by means of tunnelling spectroscopy using van der Waals heterostructures of h-BN/graphene/WS2/metal. The monolayer graphene electrodes provide for weak screening of electric-fields, which allows us to tune the chemical potential of WS2 with the back-gate. The obtained conductance maps as a function of bias and gate voltage reveal single-electron transistor behaviour (Coulomb blockade) with a rich set of transport features like excited states and negative differential resistance regimes. Moreover, by applying a perpendicular magnetic field, we study the spin ground- and excited states of single defects. |
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T70.00296: Spin Polarized Excitonic Superfluids in Topological Insulators Henry Travaglini
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T70.00297: Finite-Size Effect in the Photonic Topological System YUHAO KANG, Azriel Z Genack Measurements of the transmission matrix of a topological system supporting edge state between metacrystal emulating quantum valley-Hall and spin-Hall effects show the disruption of ballistic propagation. We observe a decrease of transmission and an increasing of the dwell time for the edge mode in a finite topological system. The non-linear spatial decrease of the logarithm of the intensity along the edge highlights the differences between transport statistics of an edge state and normal 1D channel. |
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T70.00298: Effect of band-offsets on the valley polarization properties of WSe2 lateral homojunctions Anil Rajapitamahuni, Nerea Ontoso, Luis Hueso, Felix Casanova Fernandez, Jose Ignacio Pascual, Reyes Calvo We have studied the effect of band-offsets on the valley polarization of lateral homojunctions composed of 1L/n-layer WSe2 flakes. WSe2 flakes are transferred onto SiO2/Si substrates using elastic film assisted micro-mechanical exfoliation. Optical microscopy combined with Raman spectroscopy is used to identify and determine the layer number of 1L/n-layer WSe2 structures. We worked with naturally occurring 1L/n-layer lateral homojunctions to eliminate the band-offsets resulting from twist angles and stacking order. Spatially-resolved photoluminescence (PL) spectroscopy measurements are performed using a scanning confocal microscope at low temperatures down to 4.2 K and in magnetic fields up to 5T. The intensity and energy position of the different excitation peaks in the PL spectra are mapped to determine the effects of inhomogeneities and band-offsets on the valley polarization properties of the lateral homojunctions. We intend to study the valley Zeeman effect in the lateral homojunctions via polarization-resolved PL spectroscopy. Our work will facilitate in understanding the effects of band alignment on the valley polarization phenomena in TMD homo/heterostructures for valleytronic applications. |
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T70.00299: Valleytronics in two-dimensional merging Dirac cone system: Universal reversible Boolean gate Yee Sin Ang, Lay Kee Ang, Shengyuan Yang Due to the logical irreverisbility, the energy efficiency of Boolean logic gates is fundamentally capped by the Landauer's waste heate generation limit of kBTlog2 per bit of irreversible operation. Here we show that valley degree of freedom in two-dimensional (2D) material can be harnessed to ressurect the logical reverisbility of classical two-input Boolean logics. The valley index manifests macroscopically in the electrical current as three distinct polarization states: two opposite valley polarizations plus one null state. These triplet of valley polarization states can be used to encode additional information, thus removing all ambiguity and recovering logical reveribility in Boolean logic gates. We use 2D merging Dirac cone system, which occurs in few-layer black phosphorus, strained graphene, and 2D topological Dirac semimetal, as a toy model to demonstrate three fundamental valleytronic building blocks: valley filter, valve, and logic gates. We show that the all-important universal reversible gate, such as the NAND gate, can be realized using this valleytronic approach. Our findings provide a new valleytronic route towards ultimately energy-efficient classical reverisble computing. |
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T70.00300: SUPERLATTICES, NANOSTRUCTURES, AND OTHER ARTIFICIALLY STRUCTURED MATERIALS
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T70.00301: Solvent and Concentration Effects Governing the Hierarchical Organization of Asphaltenes: A Small-Angle X-Ray Scattering Study Hasan Rahman, Jose L Banuelos Asphaltenes are a group of planar molecules found in crude oil and are prone to aggregation which causes blockage of pipes along the oil production stream. The solution-state nanostructure of various asphaltene solutions was studied using small-angle x-ray scattering (SAXS) (over a Q-range of 0.008 - 0.4 Å-1) in order to understand solvent and concentration effects on asphaltene hierarchical organization. The fractal aggregate structure of asphaltenes was characterized as a function of concentration in toluene (1-50 mg/ml), tetrahydrofuran (1-500 mg/ml), and benzene (1-100 mg/ml). In toluene, the varying cutoff length, primary radius parameters, and the growing mass fractal dimension, all suggest that at a certain chain length, asphaltene nano-aggregates (NA) begin to collapse onto themselves to form a larger and denser aggregate. The experimental data has also been fit with several models including the Unified Power Law and the Ellipsoidal/Spherical Hayter Mean Spherical Approximation models to compare their characteristic parameters such as the ‘Guinier Radius’ and ‘Porod Slope’ to develop a consistent view of the hierarchical structure of asphaltene which will aid as a valuable input to develop strategies to mitigate the effects of asphaltene aggregation. |
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T70.00302: A generalised shapelet-based method for analysis of nanostructured surface imaging Nasser Abukhdeir, Thomas Akdeniz The determination of quantitative structure-property relations is a vital but challenging task for nanostructured materials research due to the presence of large-scale spatially varying patterns resulting from nanoscale processes such as self-assembly and nano-lithography. Focusing on nanostructured surfaces, recent advances have been made in automated quantification methods for translational order using shapelet functions, originally developed for analysis of images of galaxies, as a reduced-basis for surface pattern structure. |
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T70.00303: Second Harmonic Generation On Hydrothermal Grown Zno Nanowires And Colloidal Nanostructures Films Dominic Tran, Christopher Valdes, Mostafa Sadoqi, Iwan Kityk, Gen Long We report a non-linear optical study on ZnO nanowires grown on FTO substrate and spin-cast colloidal nanostructures (PbS and PbS-Au) based films for the first time. Zinc oxide (ZnO) nanowire was grown by hydrothermal method on pre-cleaned, seeded FTO substrates, placed facedown in the aqueous solution of zinc nitrate hydrate and HMTA (Hexamethylenetetramine) for a few hours. The diameters diameters, lengths and density of ZnO nanowires could be controlled by varying seeding concentration, growth temperature and growth time. |
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T70.00304: Ion-implanted silver nanoparticles for metal-enhanced fluorescence Shahid Iqbal, Mohammad Hatshan, Prashanta Niraula, abubkr arzaq, hasna Abdullah, Ramakrishna Guda, Asghar Kayani Metal Enhanced Fluorescence (MEF) has promising applications in the field of optical displays, bio-sensing and photodynamic therapy. In this work, we exploit the plasmons of embedded silver nanoparticles (Ag-NPs) fabricated by ion implantation to enhance the fluorescence of Coumarin 515 dye (C515) via MEF. Ion Implantation of 70 keV Ag ions in quartz matrix at different fluences was carried out to synthesize Ag-NPs inside quartz matrix. The formation of Ag-NPs is characterized by the optical absorption measurements. Rutherford Backscattering Spectrometry (RBS) measurement was used to obtain the depth profile and concentration of silver within the substrate. From the RBS results, it was determined that front edge of the layer containing Ag was formed at an average depth of 16 nm below the surface, which closely agreed with Stopping and Range of Ions in Matter (SRIM) calculations. The MEF of drop casted C515 dye was studied using steady-state emission and excitation spectra measurements. Photoluminescence (PL) enhancement factor ranging from 1.2 to 2.1 with a maximum enhancement for the largest fluence was obtained. The observed MEF was ascribed to a combination of plasmon enhancement with larger nanoparticles due to increase in fluence and to increase plasmonic hot spots. |
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T70.00305: Reflection from bare and gold coated InP nanowire arrays ChiaWei Tu, Qian Gao, Hoe Tan, Chennupati Jagadish, Masoud Kaveh-Baghbadorani, Heidrun Schmitzer, Martin Fraenzl, Hans-Peter Wagner We investigated the spectral and angle resolved reflectance from bare and gold coated (plasmonic) InP nanowire (NW) arrays which were grown by selective area epitaxy. The NWs in the arrays have diameters of 180 nm, heights of ~2 and ~1 micrometers and a pitch of 666 and 500 nm (named areas NWA-1 and NWA-2), respectively. In NWA-2 the NWs additionally possess a 10 nm thick surrounding Al2O3 layer to reduce surface state and metal induced band-bending. A nominally 10 nm thick gold layer was deposited around the NWs in both arrays to study the influence of plasmonic effects. The NW arrays were illuminated with a cw laser at 880 nm for the angle resolved reflectance measurements and with an incandescent light sourced ranged from 500 nm to 1000 nm spectrally resolved experiments. The incident light beams were polarized in p- and s-orientation. The measured spectral and angle resolved reflectance of both uncoated arrays is in very good agreement with finite-difference-time-domain (FDTD) simulations. The experimental results of the gold coated nanowire arrays reveal deviations compared with the FDTD calculations which is tentatively attributed to the granularity of the deposited gold films. |
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T70.00306: Compact localized states in open scattering media Fabrizio Sgrignuoli, Malte Röntgen, Christian Morfonios, Peter Schmelcher, Luca Dal Negro In this work, we study the compact localized scattering resonances of periodic and aperiodic chains of dipolar nanoparticles by combining the powerful Equitable Partition Theorem (EPT) of graph theory with the spectral dyadic Green’s matrix formalism for the engineering of embedded quasi-modes in non-Hermitian open scattering systems in three spatial dimensions. We provide analytical and numerical design of the spectral properties of compact localized states in electromagnetically coupled chains and establish a connection with the distinctive behavior of Bound States in the Continuum. Our results extend the concept of compact localization to the scattering resonances of complex open systems with aperiodic order beyond tight-binding models, and are relevant for the efficient design of novel photonic and metamaterials architectures with enhanced light-matter interactions |
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T70.00307: Simulations of Nanostructure Plasmonic Resonators Parveen Kumar Semiconductor nanostructures with and without plasmon enhancement are studied and explored extensively for nanodevice applications ranging from bio/chemical sensors to medical monitors and photovoltaics. Plasmonic resonances strongly depends on the size, shape, spacing and interaction of metal nanoparticles with semiconductor nanostructure. A lot of resources as well as efforts are required to realize plasmonic resonator devices and optimization with different shapes and sizes. In contrast, device modeling and simulations offer a much economical substitute to tackle such challenges. To solve this problem in most economical and reliable mode, is to use Maxwell equation solver which helps in simulating the nanoparticles as surface plasmon resonator on the top of semiconductor nanostructures. The sharp features as well as the nanoparticle asymmetry is usually used for reported the enhancement of the electric field. To enhance the absorption rate as well as the photocurrent signal, I report the simulation the electrical field profile for spherical, cylindrical, and bipyramidal nanoparticles (of different materials) and model the interaction of these nanoparticles with semiconductor nanostructures. |
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T70.00308: Novel Two-Dimensional Tellurium Allotropes from the First-principles Predication Chunyao Niu, Chunxiang Zhao, Xiaolin Cai, Chaosheng Lian, Zhili Zhu, Yu Jia Very recently, the successful predication and synthesis of α-, β-, and γ- tellurene have extended the two-dimensional (2D) materials family to group-VI elements and provided new candidates for next-generation electronic and optoelectronic applications. Based on our previous work,we have furtherpredicted 33 newly 2D tellurium allotropes with mono- and multi-layers of tellurium atoms using the particle-swarm crystal structure searches methods andthe first-principles calculations. Thestabilityof these 2D structures is well verified by the total energy calculations, as well as phononspectrum calculations.Four kinds of new allotropes are found energeticallymore stable than the β-Te phase which already has been synthesized experimentally.Among these structures, we found three of them exhibittopological properties and two with superconductorproperties. The present findings enlarge the family of tellurene and will stimulate future experimental studies to synthesize novel group-VI 2D materials. |
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T70.00309: Light stops at exceptional points Tamar Goldzak, Alexei A Mailybaev, Nimrod Moiseyev Light travels in vacuum with a constant speed of 300,000,000m/sec, almost twenty years ago the light was slowed down to less than 10-7 of its vacuum speed in a cloud of ultracold atoms of sodium. Upon a sudden turn-off of the coupling laser, a slow light pulse can be imprinted on cold atoms such that it can be read out and converted into photon again. Alternatively, the light can be stopped at the band edge in photonic-crystal waveguides. Here we extend the phenomenon of stopped light to the new field of parity-time (PT) symmetric systems. |
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T70.00310: Quantum to Classical Transitions in Multilayer Plasmonic Metamaterials Evan Simmons, Kun Li, Andrew Briggs, Seth Bank, Daniel Wasserman, Viktor Podolskiy, Evgenii Narimanov Electromagnetic response of noble metals, transparent conducting oxides, and highly doped semiconductors are all dominated by the dynamics of their free electron plasma. AlInAs/InGaAs heterostructures have emerged as a reliable platform that provides epsilon-near-zero, plasmonic, and hyperbolic responses in the important mid-infrared frequency range. The electromagnetic properties of semiconductor multilayers can be related to the properties of individual layers via effective medium theory (EMT). It is typically assumed that the validity of EMT improves as the layers in metamaterials become thinner. However, quantum-confinement is expected to affect the dynamics of the free charges in ultra-thin layers. In this work, we analyze, experimentally, analytically, and numerically, the optical response of semiconductor designer metal multilayers that undergo transition from bulk to quantum-confined regime. We demonstrate that this transition can be used as a doping-independent control mechanism to engineer the optical response of designer metals and the optical topology of the resulting multilayer metamaterials. |
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T70.00311: Interlayer excitons at the tunable Moire line defect Jianju Tang, Hongyi Yu, Wang Yao Van der Waals stacking of two monolayers semiconducting transition metal dichalcogenides is a powerful approach to create semiconductor heterojunctions for engineering functional devices. The inevitable mismatch in lattice constants and crystallographic axes leads to the formation of Moire pattern, giving new possiblilities to tailor the material properties. Interlayer excitons in such moire pattern experience an effective superlattice potential and have a nanoscale patterned light-coupling properies. The low energy physics of those excitons can be described by a tight binding model with giant spin-orbit coupling. Here, we investigate interlayer excitons in such moire pattern with a line defect due to the twin domain boudary in one of the layers, which can localize one-dimensional excitonic modes of topological origin. We show that the defect configuration in the Moire superlattice can be tuned by the interlayer translation, twisting angle and reflects the atomic configuration of the domain boundary. The effects of the Moire line defect configuration on the exciton modes are systematically investigated. We also find the defect exciton mode has distinct light-coupling properties on the two sides of the twin domain boundary. |
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T70.00312: Photoluminescence studies of lysozyme mediated zinc oxide (ZnO) nanoparticles Nikesh Maharjan, Mim L Nakarmi, Deependra Das Mulmi, Naresh M Shakya Ultraviolet Photoluminescence spectroscopy was employed to study optical properties of lysozyme mediated zinc oxide (ZnO) nanoparticles. The Zinc oxide nanoparticles using lysozyme (L: ZnO) were prepared through a facile synthesis. The samples were annealed at 550 oC for 2 hours. Third harmonic laser (260 nm) generated from the Ti: sapphire laser was used for optical excitation in the experiments. Photoluminescence spectrum measured at low temperature has emission peaks around 3.3 eV and a broad emission around 2.45 eV. We performed temperature and excitation power dependent photoluminescence measurements to identify the origin of the emission peaks in the spectra. We will present our findings on the optical properties of lysozyme mediated zinc oxide nanoparticles and discuss the effect of lysozyme in the optical properties of ZnO nanoparticles. |
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T70.00313: Phonon induced resistance oscillations (PIRO) caused by THz laser Beate Horn-Cosfeld, Mihai Cerchez, Thomas Heinzel PIRO terms the magneto-resistance (MR) oscillation originating from the resonant interaction of 2D electrons with thermal acoustic phonons [1], observed only in very high mobility samples (>107 cm2V-1s-1) [2]. |
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T70.00314: Tunability of thermal conductivity in low-dimensionality chalcogenide and pervoskite heterostructures Mack Adrian Dela Cruz, Nick Boecker, Gary Pennington Recent work in lead chalcogenide alloys of PbSe, PbS, and PbTe has shown interesting electronic properties. Perovskites, such as SrTiO3, have been the focus of much research in the past few years. The thermal properties of such materials are of interest for thermoelectric applications. We further consider low-dimensionality heterostructures, which generally have lower thermal conductivities compared to bulk. We use a computationally efficient shell model to find the phonon dispersion of bulk, and approximate the heterostructure phonon dispersions. Phonon Transport is modeled with a Monte Carlo formulation of the Boltzmann transport equation using an interfering particle method with phonon-phonon scattering, boundary scattering, defect scattering, interface scattering, and quantum confinement. We will report on the tunability of thermal conductivity by manipulating low-dimensionality heterostructures of these lead chalcogenide alloys and perovskites. |
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T70.00315: Determining Phonon Density of States in Nanomaterials from Optical Fluorescence Desmond Wuhan Cai, Ding Ding, Kezhi Zheng, Xian Qin, Xiaogang Liu Thermal transport in nanomaterials have attracted a lot of attention in recent years but measuring thermal transport accurately remains a challenge. While size effects play a great role in influencing thermal transport through ballistic and coherent effects, they also influence the phonon density of states (PDOS). So far, direct measurements of PDOS with neutron scattering is difficult to perform on nanomaterials and Raman scattering is the only experimental technique available to validate a theoretically predicted PDOS from a nanomaterial. Here, we propose and evaluate a numerical technique to obtain PDOS directly from temperature dependent optical lineshape information of a fluorescent nanomaterial. We show that such a technique can be used to resolve distinct PDOS features that are results of geometric confinement. Our numerical technique uses a convex approach which is very efficient and is able resolves complicated PDOS lineshapes compared to earlier techniques of deriving PDOS from specific heat. We believe this technique can enable the development of novel nanomaterial designs for better thermal management and thermoelectrics. |
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T70.00316: Phonon backaction in diatomic molecular junctions: Negative differential conductance, quantum interference and super-Poissonian noise Tae-Ho Park, Han-Yong Choi We present a study of the non-equilibrium electron transport through diatomic molecular junctions employing the full counting statistics (FCS) in combination with the self-consistent Born approximation (SCBA). Here, we consider two different types of electron-phonon coupling in a molecule. One is the coupling of the molecular vibration to the electrons in each orbital (intra-orbital coupling) and the other is to the transferring electrons (inter-orbital coupling). We show that the super-Poissonian noise is enhanced by increasing the electron-phonon coupling in the presence of the phonon backaction. In the weak coupling regime for the inter-orbital coupling, the negative differential conductance (NDC) can take place in the resonant tunneling regime. It turns out that the current fluctuation suppresses NDC, but induces the quantum interference in molecular conductance. |
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T70.00317: ABSTRACT WITHDRAWN
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T70.00318: Phonon-Plasmon Scattering and Localization in Graphene Structures Brahmanandam Javvaji, Debiprosad Roy Mahapatra In this paper we discuss about a self-consistent model of phonon-plasmon coupled dynamics and investigate the nature of the coupling in the graphene nanostructures. Effect of length-scale in three types of structures namely graphene nano-ribbon, graphene on silicon and graphene defects are investigated. Nonlinear conversion arising from aperiodic localization of phonon modes in the nanoribbon are observed. We show how the chirality plays a role on this relationship. Effect of silicon substrate atoms on the dynamics are analyzed. We then review the present understanding and new ways to design thermal energy transport in graphene based optoelectronic devices. Another aspect of phonon generation is plasmonic extinction due to RF, field emission or lasing with application in filters or sensors. In context of these ideas, we show how the structure of defects in graphene alters the plasmonic extinction. The charge localization around the defects are studied in details and the stability limits of the defects in terms of size and shape are analyzed. To this end, new results showing signature of these instabilities in the optical spectra and phonon spectra will be discussed. |
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T70.00319: Nanoscopic Hyperlensing from Natural and Monoisotopic Hexagonal Boron Nitride Crystals Swathi Iyer, Alexander Giles, Sai Sunku, Thomas Folland, Nicholas Sharac, Song Liu, James H. Edgar, Dimitri Basov, Joshua D Caldwell Hyperbolic media, where the permittivity is opposite in sign along orthogonal axes, support highly directional propagation of volume-confined, hyperbolic polaritons (HPs) for use in super-resolution imaging via the hyperlens concept. Hexagonal boron nitride (hBN), a natural hyperbolic material, supports deeply subdiffractional, low-loss HPs in both planar slabs and nanoscale resonators within the mid- to long wavelength IR. These losses could be reduced even further by using monoisotopic (i.e. material with just a single boron isotope) hBN. Here we exploit these ultralow losses and natural hyperbolic response to realize unprecedented spatial resolution in hyperlensing with long-wavelength IR light. We provide a direct comparison of the imaging power of hyperlens designs using flat slabs of naturally abundant and monoisotopic hBN via scattering-type near field optical microscopy (s-SNOM). Our experimental (s-SNOM) and simulated results show the ability to resolve features as small as 50 nm with 6-7.1 µm free-space wavelength light, providing at least l/125 spatial resolution. We complement this with electromagnetic field simulations of the hyperlens response to demonstrate and quantify the improvements from the monoisotopic over the naturally abundant materials. |
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T70.00320: Thermal transport in holey silicon membranes investigated with optically-induced transient thermal gratings Ryan Duncan, Giuseppe Romano, Marianna Sledzinska, Alexei Maznev, Jean-Philippe Peraud, Olle Hellman, Clivia Sotomayor Torres, Keith Adam Nelson In semiconductor nanostructures with feature sizes on the order of 100 nm, thermal transport is expected to be well-described by the phonon Boltzmann transport equation (BTE) with diffuse boundary scattering. However, over the past several years there have been reports of anomalously low effective thermal conductivity values in one- and two-dimensional semiconductor nanostructures. In this study, we investigate thermal transport in nanostructured holey silicon membranes using the non-contact optical transient thermal grating (TTG) technique. We compare the experimental results with two ab-initio BTE numerical techniques. We obtain excellent agreement between theory and experiment, indicating that semiclassical Boltzmann transport theory for phonons is adequate for describing thermal transport in semiconductor nanostructures with feature sizes on the order of 100 nm. |
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T70.00321: OpenBTE: A Multiscale Solver for the Phonon Boltzmann Transport Equation Giuseppe Romano We present OpenBTE, an open-source tool to compute heat transport in nanostructured materials with arbitrary shape and dimensionality. The code solves the space-dependent Boltzmann transport equation taking into account the material’s Brillouin’s zone and diffuse boundaries. For phonon mean-free-paths (MFP) that are much smaller than the characteristic length of the material, we employ a heat diffusion solver so that we lift most of the computational load with negligible loss in the accuracy [1,2]. After an introduction to OpenBTE’s main features, we will show the software architecture, including parallelization and interfaces to popular first-principles phonon solver. Then, we illustrate key examples and comparison with experiments. A brief tutorial will conclude the talk. |
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T70.00322: Symmetry selective oxygen orbital polarization in spinel Al2O3 films Ruyi Zhang, Yang Song, Yanwei Cao Orbital polarization is common for the 3d orbitals of cations as a result of strain, symmetry breaking, or charge transfer, but very rare for 2p orbitals of simple anions. Here, we report a symmetry-selective measurement of orbital polarization for O 2p orbitals in γ-Al2O3/SrTiO3 thin films via linearly polarized X-ray absorption spectroscopy (XAS) at the O K-edge. The O 2p orbitals with octahedral coordination exhibit a large subband splitting exceeding ~ 0.35 eV, while those with tetrahedral coordination show a very weak orbital polarization. These results pave a new way to engineer band structure and quantum states of functional oxide materials via local symmetry effects on anion orbitals. |
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T70.00323: d-orbital symmetry of BaTiO3 thin film Yang Song, Ruyi Zhang, Yanwei Cao A high-quality BaTiO3 thin film was grown on a DyScO3 single crystal substrate using pulsed laser deposition. Soft X-ray absorption spectroscopy was performed at the Ti L2,3 edges of the film to characterize the d-orbital symmetry. Novel split Ti d-orbital eg and degenerate t2g subbands of the BTO film have been observed. The energy of dx2-y2 orbital is lower than the d3z2-r2 orbital by about 100 meV, the opposite of what would normally be expected for Jahn-Teller octahedral distortion. This is likely a result of the displaced Ti cation. This novel d-orbital symmetry is very likely to be found in other perovskite-based ferroelectric materials. |
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T70.00324: WITHDRAWN ABSTRACT
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T70.00325: Modulation doping in SrSnO3/BaSnO3 heterostructures Abhinav Prakash, Nicholas F Quackenbush, Hwanhui Yun, Jacob T Held, Tianqi Wang, K. Andre Mkhoyan, Bharat Jalan Through a combination of MBE growth, hard X-ray photoelectron spectroscopy (HAXPES), magnetoresistance measurements and transport modeling, we report on the realization of two-dimensional electron gas (2DEG) at SrSnO3/BaSnO3 (SSO/BSO) heterointerfaces. The HAXPES revealed the valence band offset between SSO and BSO to be 0.7 eV resulting in a favorable conduction band offset for modulation doping of BSO using SSO as a spacer layer. Two-channel conduction suggested by the non-linear transverse hall resistance as a function of magnetic field revealed the transfer of electrons from La-doped SSO to BSO. The sheet carrier density on the BSO side was measured to be 5×1012 cm-2 consistent with the value obtained using a self-consistent solution to one-dimensional Poisson and Schrödinger equations. The role of band offset, interface roughness and threading dislocations in BSO will be discussed with the goal to obtain high mobility oxide heterostructures. |
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T70.00326: Magnetic Structure in Entropy Stabilized Single Crystal Spinel Ferrite Films Yogesh Sharma, Alessandro Mazza, Elizabeth Skoropata, Liam Collins, Zheng Gai, Thomas Ward “Entropy-stabilized oxides” possess large configurational entropy driven by the multi-cation disorder which dominates over the enthalpy of formation. The random distribution of constituent elements into the cation sublattice(s) enhances the configurational entropy. These oxide systems possess new possibilities for generating complex electronic and magnetic states due to the near degeneracies of cation spin-charge-orbital order parameters. Here, we grow single-crystal epitaxial thin films of extremely configurationally disordered spinel ferrites. We find that high entropy spinel oxide (HESO) films of (Mg0.2Ni0.2Fe0.2Co0.2Cu0.2)Fe2O4 grown on various substrates—MgAl2O4 (MAO), MgO, and SrTiO3 (STO)—demonstrate an interesting array of magnetic properties in terms of long-range stripe domains, strain-controlled magnetic anisotropy, unusual element-specific magnetization, and magnetic phase transition well above room temperature. The extreme number of cations and configurational degeneracy is expected to open many new avenues for fundamental physics and applied works. |
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T70.00327: Theoretical study of piezotronic metal–insulator–semiconductor tunnel devices Xiaolong Feng Piezotronics has been an emerging concept coupling piezoelectric and semiconducting properties with potential applications in sensors, flexible electronics and nanoelectromechanical systems. Piezoelectric field is created under an applied strain, which controls the carrier generation, transport, separation or recombination processes at the interface or junction of the semiconductor devices. Based on the piezotronic theory, we present a 1D model for the metal–insulator–semiconductor (MIS) tunnel diode based on the piezoelectric semiconductor. Analytical solutions of piezoelectric modulated tunneling are described to reveal the piezotronic effect on the MIS tunnel junction. A numerical simulation of the carrier transport properties is provided for demonstrating the piezotronic effect on MIS tunnel devices. |
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T70.00328: Rare-earth metal organic frameworks for quantum information applications Donny Pearson, Elizabeth Goldschmidt, Haoquan Fan Rare-earth atoms in solids are excellent candidates for atomic ensemble-based quantum memory due to their long-lived optical and spin lifetimes, high density of emitters, and suitability for photonic integration. In rare-earth doped systems, a major problem implementing long-lived, efficient quantum memory is the inhomogeneous broadening of the energy levels due to the site-to-site variations, which in doped materials is primarily caused by the dopant itself. Crystals that are stoichiometric in the rare-earth atom, i.e. the rare-earth species is part of the chemical formula of the crystal rather than a substitutional dopant for some element, have demonstrated the potential for smaller inhomogeneous line widths due to the lack of doping induced disorder. We investigate the potential of metal organic frameworks to host rare-earth atoms with narrow optical inhomogeneous linewidth as a platform for quantum memory and other related applications. We will present progress towards growing macroscopic single crystals and initial optical measurements of these high-density, rare-earth ensembles. |
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T70.00329: Spectroscopy of Erbium-167 doped yttrium orthosilicate for quantum photonic technologies Mi Lei, Ioana Craiciu, Jake Rochman, Jonathan Kindem, John Bartholomew, Andrei Faraon Rare-earth ions in crystals are one of the most promising candidates for quantum memories due to their long optical and spin coherence times. They have been used to realize solid-state quantum memories in bulk crystals and in nanophotonics devices. Erbium is of particular interest because it has an optical transition in the telecom band, which allows integration with silicon photonics and telecommunication compatibility. Recently, erbium-167 doped yttrium orthosilicate has been shown to have good properties for quantum memories. With a nuclear spin of 7/2, erbium-167 has 16 hyperfine levels in the optical ground state manifold, which can be used as shelving levels for spectral holeburning, and to store coherence in the nuclear spin. |
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T70.00330: PARADIM REU Project Title: STEM Imaging and Composition Mapping of Multiferroic Oxides Anthony Coleman
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T70.00331: Epitaxial Growth of Phosphorus Nanostripe Arrays on Cu(110) Shuo Sun, Jialin Zhang, Songtao Zhao Black phosphorus has attracted significant attention as a new emerging two-dimensional (2D) material in recent years. New 2D phosphorus allotropes with various structures have also been predicted by theoretical calculations. It has been theoretically predicted that substrate plays a critical role in stabilizing phosphorus nanoflakes on surface. Here, we report a molecular-beam-epitaxial growth of phosphorus nanostripe arrays on Cu(110) by using black phosphorous as precursor, through the combination of in-situ low temperature scanning tunneling microscopy (STM), low energy electron diffraction, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Atomically resolved STM image and the corresponding DFT simulations reveal that phosphorus atoms are adsorbed on top of the valley copper atoms and arranged periodically to form nanostripe arrays. XPS and Bader charge analysis confirm a significant charge transfer from the Cu(110) substrate to P atoms on top. |
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T70.00332: Nitrogen-Vacancy (NV) centers in Nano diamonds: Toward optimization and photo stability Ravi Kumar, Dilip Kumar Singh, Sanjay R. Dhakate Nitrogen-Vacancy (NV) centers in Nano diamonds (NDs) are one of the most promising room temperature atom like system for an array of present and future technological applications. These include bio imaging, nano metrology and quantum information processing (QIP). All of these applications depend upon the optimized concentration of NV centers (NV- ) in NDs and their photo stability over continuous excitation. Both of these factors i.e. optimization of concentration of NV centers and their stable photo-physical behavior are major hurdles for different applications. In the present work, we have optimized the fabrication condition for the efficient creation of NV centers. Interestingly, we have successfully created the uniform concentration of NV centers in NDs by dispersed low energy ion irradiation . While investigating the effect of surface functionalization, it was revealed that different degree of surface oxidation of NDs leads to different photo-stability of NV centers. With the optimized concentration of NV centers, we have observed the single photon emission at room temperature and optical bio imaging. Our findings provide new insight to achieve the optimized as well as photo-stable concentration of NV centers and prepare the platform for wide range of applications of NDs. |
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T70.00333: Tin catalyzed-silicon nanowires prepared by solid-liquid-solid mechanism Kaigui Zhu, Khamis Masoud The fabrication of silicon nanowires (SiNWs) catalyzed by low melting metal through solid-liquid-solid (SLS) mechanism makes it very useful in electronic device applications. However, little research has been done in combining SLS mechanism with Sn catalyst deposited as continuous film by magnetron sputtering system to grow SiNWs. The growth of Sn catalyzed-SiNWs through SLS mechanism by thermal annealing technique on a Si <100> substrate was investigated, and initially Sn catalyst was deposited as a continuous film by magnetron sputtering system. Randomly and voluminous SiNWs are observed on the Si substrate after 1000 0C annealing process with a feature that looks like a tree having many numbers of long branches of SiNWs. These confirm the growth of Sn catalyzed-SiNWs through SLS mechanism, with Sn catalyst initially being deposited as a continuous film. |
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T70.00334: Modeling the Growth of Salt Nano-Wires Charles Ay, Gary Pennington
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(Author Not Attending)
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T70.00335: Synthesis and characterization of Co-based magnetic nanowires Pok Lam Tse Pure Co, pure Cu and Co/Cu two-segment nanowires with high pore filling rate and uniform sizes were successfully synthesized through the direct electrochemical deposition in Anodic Aluminum Oxide (AAO) membrane. By applying different deposition currents in a single mix bath, nanowires with different materials and different crystal structure were fabricated. The length of the nanowires is several micron and diameter is between 80-100 nm. The pure Co nanowires and the Co segment in the Co/Cu nanowires show hexagonal close packed (hcp) crystal structure. The pure Cu nanowires and the Cu segments in Co/Cu nanowires show face centered cubic (fcc) structure. Magnetic force microscopy (MFM) analysis illustrates the quasi-periodic magnetization modulation along the pure Co wires and the Co segment in Co/Cu two-segment nanowires. A pair of Co/Cu two-segment nanowires partially in contact showed magnetization interactions at the Co segments. The magnetization modulation is explained by the competition between shape anisotropy and magnetocrystalline anisotropy. |
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T70.00336: Interaction Effects in Open Nanoelectromechanical Systems Bilal Tanatar, Valeriu Moldoveanu, Radu Dragomir, Stefan Stanciu We discuss the transient and steady-state transport properties of nanoelectromechanical systems (NEMS) in the quantum regime. |
(Author Not Attending)
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T70.00337: Topological Insulator Sb2Te3 and Phase Change Material GeTe Nanowires Synthesis and their Electrical Properties Measurements Pok Lam Tse Sub-100nm topological insulating(TI) Sb2Te3 nanowires(NWs) and phase change material GeTe nanowires were fabricated by Catalytic Chemical Vaporized Deposition(CVD). The Vapor-Liquid-Solid(VLS) growth mechanism in the fabrication process effectively decreased the growth temperature to around 400°C from around 600-800°C. The stoichiometry ratios of Sb2Te3 NWs(2:3) and GeTe NWs(1:1) had been measured by energy-dispersive X-ray Spectroscopy(EDX) analysis along the NW samples. For the electron spin transports in TI, Magnetic Tunnel Junction contacts at 4K showed a sharp conductance change of non-local magnetoresistance at ±0.5kG, indicates the spin momentum locking effect of topological insulator. P-type conduction property of Sb2Te3 nanowire1 was measured by the field effect transistor(FET) measurement at 68K with back gate voltage up to 100V across 300nm SiO2 dielectric layer. Phase change property of GeTe nanowire was tested for crystalline and amorphous transition by applying 3V to 5V voltage few hundred ns width voltage pulses, the crystalline form had a resistance at about few kilo-ohm and the amorphous form was at about 30k ohm to 1M ohm range. Preliminary results showed 10 to 20 cycles of switching with no degradation. |
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T70.00338: The observability of Quantum Pinch Effect in the magnetized semiconducting Quantum Wires Manvir Kushwaha We investigate a two-component, cylindrical, quasi-one-dimensional quantum plasma subjected to a |
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T70.00339: Collective excitations in quantum wires made up of vertically stacked quantum dots Manvir Kushwaha We report on the theoretical investigation of the elementary electronic excitations in a quantum wires made up of vertically stacked self-assembled InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the experimental setups prompt us to consider an infinitely periodic system of two-dimensionally confined (InAs) quantum dot layers separated by GaAs spacers. Since the wells and barriers are formed from two different materials, we employ the Bastard's boundary conditions in order to determine the eigenfunctions along the z direction. We compute and discuss the behavior of the single-particle and collective excitations and finally size up the importance of studying the inverse dielectric function in relation with the quantum transport phenomena. It is remarkable to notice how the variation in the barrier- and well-widths can allow us to tailor the excitation spectrum in the desired energy range. Given the advantage of the vertically stacked quantum dots over the planar ones and the foreseen applications in the single-electron devices and in the quantum computation, it is quite interesting and important to explore the electronic, optical, and transport phenomena in such systems. |
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T70.00340: Single-Molecule Super-Resolution Fluorescence Lifetime Microscopy Zachary Hallenbeck, Nathan Kimmitt, Esther A Wertz The environment of an emitter has a remarkable impact on its emission properties, and on its lifetime in particular. Emitters coupled with plasmonic nanoparticles show enhanced emission rates, dependent on their proximity and orientation with respect to the nanoparticles, and on the overlap in wavelength between emission and plasmon resonance. We propose a method that combines fluorescence lifetime imaging microscopy with single-molecule super-resolution microscopy to study these properties with spatial resolution below the diffraction limit and picosecond time domain resolution. In order to study single molecule emission in these environments, a nanoscale emitter must be immobilized long enough to confocally scan over its diffraction limited emission. This challenge wil be overcome using fast scanning speeds and careful dye deposition. Combining single-molecule super-resolution microscopy with fluorescence lifetime imaging techniques allows for a new level of precision and isolation that avoids the loss of information associated with ensemble averaging. Our study will provide new insight into the physics of plasmonic environments which will be essential to the development of plasmonic technology in growing fields like biomedicine, nanoscale imaging, and quantum information. |
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T70.00341: Highly luminescent Lead Depleted Cs4PbBr6 Nanocrystals via Saponification Synthesis at an Ambient Atmosphere Gopi Adhikari, Saroj Thapa, Hongyang Zhu, Peifen Zhu Lead halide perovskites have proven themselves to be promising materials for applications in optoelectronic devices because of their excellent photophysical properties, however, the synthesis of those nanocrystals has until now, been too complex. Our newly developed saponification approach was employed to synthesize all-inorganic halide perovskites at an ambient atmosphere. We reported the conversion from three-dimensional CsPbBr3 to lead depleted zero-dimensional Cs4PbBr6 nanocrystals by altering the amount of Cs-oleate precursor at a low-temperature synthesis so that the transformation remarkably changes the properties of the nanocrystals. The XRD spectra, TEM images, absorption and photoluminescence spectra have been taken for the systematic study of properties of CsPbBr3 and Cs4PbBr6 nanocrystals. The CsPbBr3 emitting a strong blue emission (460 nm) and is shifted to the green region (528 nm) for Cs4PbBr6, which demonstrates the intrinsic luminescence nature of the Cs4PbBr6 nanocrystals. In addition, the lead depleted Cs4PbBr6 structure is of great interest that minimizes the chemical instability, and particularly, toxicity issues. These exciting properties offer them an advantage to be used in optoelectronic devices. |
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T70.00342: Hydrostatic pressure effect on the intraband absorption coefficient in a core-shell spherical GaAs/AlxGa1-xAs quantum dot K. A. Rodríguez-Magdaleno, Juan Carlos Martinez Orozco In this work we present the intraband absorption coefficient calculation in a core-shell spherical GaAs/AlxGa1-xAs quantum dot. The quantum dot is composed of GaAs and surrounded by three shells of AlGaAs and GaAs, respectively. The electronic structure is calculated within the effective mass approximation and considered the hydrostatic pressure effect using a numerically stable transfer matrix method. The intraband absorption coefficient is computed by means of the Fermi's Golden rules under the dipolar matrix approximation. We reported the absorption coefficient between the 1s and 1p states as a function of the internal and external radius size, Aluminium concentration and the hydrostatic pressure. The results show that the absorption coefficient undergoes a change in the magnitude as well as in the resonance peak location. These results can be used to improve the absorption tuning and could be useful for enhance the solar devices. |
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T70.00343: Color Tunable All-Inorganic Mixed Halide Perovskites for Optoelectronic Applications Saroj Thapa, Gopi Adhikari, Hongyang Zhu, Peifen Zhu
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T70.00344: Auto-Desiccating Synthesis of Lead Halide Perovskite Nanocrystals via a Saponification Process Preston Vargas, Gopi Adhikari, Hongyang Zhu, Peifen Zhu In this work, a new process is developed to synthesize lead halide perovskite nanocrystals with the goal of reducing the manufacture cost. By using a saponification reaction to create the cesium precursor solution, synthesis can be achieved at room temperature and without the use of a vacuum oven. Blue-green tunable emission is obtained by varying the synthesis temperature. The crystal phase of the nanocrystals exhibit an increasingly directionally aligned orthorhombic phase with increasing temperature. Also, the saponification process uses low-cost compounds to produce the cesium precursor. Furthermore, the moisture instability of halide perovskite nanocrystals is well managed by this process because the highly hygroscopic by-products in this process auto-desiccate the reactants. Therefore, the nanocrystals can be efficaciously synthesized in an air atmosphere without interference from local humidity. This provides an accessible and low-cost pathway for synthesizing this material outside of controlled laboratory conditions. |
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T70.00345: Nonlinear optical properties of double asymmetric AlxGa1−xN/GaN quantum wells considering strain effects Flavio Manuel Nava Maldonado, Jose Guadalupe Rojas Briseño, Miguel Eduardo Mora Ramos, Juan Carlos Martinez Orozco A theoretical study has been carried out to investigate the optical absorption coefficient and the relative change in the refraction index in asymmetric double zinc-blende AlxGa1−xN/GaN quantum wells. Highlighting the effect of lattice strain on these properties. |
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T70.00346: Principal transport properties of α-T3 model in the presence of external irradiation. Dipendra Dahal, Godfrey Gumbs, Andrii Iurov, Danhong Huang Using a simplified s-wave approximation approach for the conventional Boltzmann conductivity |
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T70.00347: Effective Plasma Frequency in Graphene-Based Photonic Crystals Ivan Fuentecilla-Carcamo, Felipe Ramos-Mendieta, Martha Palomino-Ovando, Alejandro Hern\'andez-L\'opez Photonic crystals, based on graphene-dielectric multilayers, have been shown to exhibit tunable Bragg gap opening due to Fermi level tunability at each graphene layer. At low Frequencies (THz regime), a metallic-like gap is also observed with a doping dependent cutoff frequency which marks the beginning of the first transmission region. In this work, we numerically analyze this cutoff frequency as a function of Fermi level, interlayer distance and immersing dielectric constant for an equally doped graphene stack immersed in homogeneous dielectric. We give an analytical approach to deduce a Drude-like effective index for a graphene-dielectric unit cell which in turn, allows to obtain an analytical formula for this cutoff frequency. We determine parameter ranges where our analytical model fits better with the data obtained by numerical computation. |
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T70.00348: Transverse Electric Mode Excitation in Graphene-Based Multilayers Through Attenuated Total Reflection Technique Felipe Ramos-Mendieta, Ivan Fuentecilla-Carcamo, Martha Palomino-Ovando, Alejandro Hern\'andez-L\'opez Graphene monolayer can support transverse electric plasmonic modes where in-plane current oscillations are present and parallel to electric field vector. These modes, as recently shown, can be excited by Attenuated Total Reflection (ATR) Technique where mode coupling is obtained above a cutoff distance between prism and graphene. In this work, we extend this analysis by considering a graphene (equally doped)/dielectric stack as supporting element. We show that Surface Plasmonic (SP) modes are excited through this technique showing smaller cutoff distances than those reported for monolayer graphene. We found that cutoff distance, dc, decreases as the number of stacked layers grows following the rule dc=α/(2n), where α is the decaying length and n is the number of graphene layers. We prove surface plasmon excitation, corresponding to minima in the ATR, by numerical calculation of dispersion relations of SPs for two, three and four graphene layers in the stacking. |
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T70.00349: Magnetic and electronic properties for rare-earth metals intercalated in bilayer graphene Alexandria Alcantara, Jason Haraldsen In this study, we examine the interaction of Dirac fermions and bosons, we investigated the electronic and magnetic properties of rare-earth-metal intercalated in bilayer graphene. Using density functional theory, we determined the electronic structure, density of states, magnetic moment, and total energy for lanthanum (La), gadolinium (Gd), holmium (Ho), and erbium (Er) in a honeycomb configuration. An analysis of the total energy and magnetic structure, shows that the Gd and Ho substitutions obtain a FM ground state, while the La and Er substitutions have an AFM ground state, which means that Gd and Ho layered sandwiches may have possible Dirac boson interactions. The electronic structure provides information on Dirac fermionic interactions. We find that the presence of rare-earth materials shifts the Dirac cone in the electronic structure into the valence band, and while Lanthanum does not provide any f-orbital interactions, Gd, Ho, and Er have strong f-orbital characteristics. However, this seems to be at the expense of the Dirac fermionic cone. |
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T70.00350: Ordered Particle Arrays via a Langmuir Transfer Process: Large Area Access to Any Two-Dimensional Bravais Lattice Miriam Mauer, Christian Stelling, Bernd Kopera, Fabian Nutz, Matthias Karg, Markus Retsch, Stephan Förster The preparation of particle arrays on solid substrates is an essential step for the fabrication of functional surfaces and thin-film devices with applications in lithography, optics, photonics, high-density data storage and as adhesive/non-adhesive surfaces. Colloidal self-assembly represents an attractive and scalable route towards hexagonally close-packed particle arrays. To significantly broaden the structural variability, the fabrication of non-close-packed and also non-hexagonal particle arrays are required. Here, we demonstrate how to fabricate non-close-packed particle arrays with symmetries of all possible Bravais lattices in a simple solution-based process. Our process starts with readily self-assembled, hexagonally close-packed monolayers, which are immobilized on an air/water interface. Upon transfer onto the target substrate, stretching along a specific crystallographic direction occurs. This yields non-close-packed structures with non-hexagonal symmetry. We demonstrate how to control the stretching factor by interfacial modification of the target substrate to access all possible Bravais lattices. |
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T70.00351: High energy particles detection through high mobility GaAs/Al0.3Ga0.7As QW Hall bar sensor Mehdi Pakmehr, Muhammad Asteraki GaAs as a well-known semiconductor has been used widely for detection and different types of sensor fabrication for diverse purposes within last decades. We used high carrier density GaAs/Al0.3Ga0.7As QW with relatively high mobility with an ultimate goal of being used to fabricate high energy particles detector. The carrier density of our samples are relatively high (ns=6.24×1011 cm-2) with hall mobility of 1.5×105 cm-2/V.s. The large Hall bars samples were fabricated form modulation doped MBE grown wafer used for our experimentations. The sample sits at the bottom of probe stick within VTI at Liquid nitrogen temperature (T=77 K) while chopped high energy particle beams (positrons) from Na22 source hit it. Through common lock-in technique we detected signal due to interaction of beam particles with 2DEGs confined within QW of our samples. We plan to present our findings through a poster at March 2019 APS meeting being held at Boston |
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T70.00352: SURFACES, INTERFACES, AND THIN FILMS
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T70.00353: The coordination of Metal-Salen to diatomic molecules Dan Liu Salen is a Schiff base complex which is condensed from salicylaldehyde and ethylenediamine. The chemical, electronic and magnetic properties of metal-salen could be altered by adjusting the central metals. These metal-salen register wide applications in materials science, heterogeneous catalysis, geology, biology and so on due to the diversity of their properties. |
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T70.00354: Icing and deicing of a sessile droplet on superhydrophobic surfaces Fuqiang Chu, Haie Yang, Dongsheng Wen Icing exist widely in nature and in industry, causing numerous problems such as imperiling the flight safety of an aircraft, deteriorating the heat transfer of a heat exchanger, and reducing the power generation efficiency of a wind turbine. When the exposed temperature is too low, icing is inevitable even on a superhydrophobic surface. So deicing is essential. In this work, we investigate the icing and deicing characteristics of a sessile droplet on an Al-based superhydrophobic surface and aim to understand the surface and interface phenomena occurred during icing and deicing. During icing, ice front always propagates from the bottom of the droplet, finally forming a singular tip at the droplet top, while the nucleation position is various under different conditions. When the surround air is very humid, the nucleation tends to appear at the solid-liquid interface of the droplet; otherwise, the nucleation appears at the liquid-air interface of the droplet. During deicing, melting also first occurs at the bottom of the freezing droplet, but the ice-water interface is more flexible compared with that during icing with obvious swaying and rotating behavior of the unmelted ice cover. The possible Marangoni effect occurred during deicing may be the reason for these behavior. |
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T70.00355: Ionic effectiveness in the self-assembly and crystallization of polymer grafted Au nanoparticles at the gas-liquid interface Wenjie Wang, Wei Bu, David Vaknin Salts in solutions promote aqueous surface self-assembly of gold nanoparticles (AuNPs) that are grafted with non-ionic and water soluble polymers such as poly(ethylene glycol) (PEG) or poly(N-isopropylacrylamide) (PNIPAM). Using AuNPs functionalized with PEG (PEG-AuNPs) as a model system, previous studies have demonstrated that ions can be ranked in their effectiveness to promote the two-dimensional superlattice formation of PEG-AuNPs. Similar ranking for the aqueous biphasic system (ABS) of PEG in salt solutions. However, we show that ionic species that do not readily induce ABS at ambient temperatures can lead to surface crystallization of PEG-AuNPs. Synchrotron x-ray reflectivity and grazing incidence small angle x-ray scattering methods are used to determine the structures of the surface assembly for various ionic species. Here, we report on grazing incidence x-ray fluorescence spectroscopic measurements that in conjunction with Compton and Thomson scattering reveal ion-specific distributions at the surface and in the bulk in the presence of PEG-AuNPs suspensions and compare them to salt solutions without NPs. We find that the ion distributions of CsCl and NaI correlate with the quality of surface PEG-AUNPs crystallization. |
(Author Not Attending)
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T70.00356: First-Principles Prediction of Temperature Dependence of Surface Wettability and Interfacial Tension in Multiphase Systems Qiaoyu Ge, Jin-You Lu, Aikifa Raza, TieJun Zhang Temperature dependences of solid surface wettability and liquid-liquid interfacial tension play important roles in many applications involving interfaces or thin films working at elevated temperature, such as subsurface energy production and organic solar cell fabrication. In this work, a first-principles approach based on ab initio molecular dynamics is proposed to reveal the insightful effect of temperature on solid surface wettability and liquid-liquid interfacial tension. Temperature-dependent adhesion and cohesion energies are calculated from ab initio molecular dynamics and used to evaluate the temperature dependency of interfacial properties. A system of calcite-water-decane is simulated to predict the contact angle of water on calcite surface in presence of decane, as well as water-decane interfacial tension at different temperatures. The predicted reduction rates of contact angle and interfacial tension with temperature agree well with our experimental validation. The first-principles nature of this method makes the prediction accurate and intrinsic, meanwhile it provides physical insight into experimental multiphase behaviors and prediction of new wetting phenomena. |
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T70.00357: Resistive switching in La0.3Ca0.7MnO3/YBa2Cu3O7-δ devices John Betancourt, John e Ordonez, Maria Gomez, Carlos William Sanchez, Wilson Lopera, Katherine Gross, Juan Ramirez We have deposited La0.3Ca0.7MnO3 (LCMO) /YBa2Cu3O7-δ (YBCO) on SrTiO3 (STO) (100) oriented substrate by sputtering technique at pure oxygen atmosphere at high pressure (4 mbar) to study the resistive switching response. We grew systematically the insulator LCMO film with different thicknesses (tLCMO= 60, 30 and 15 nm) on YBCO layer (tYBCO= 60 nm), which acts as bottom electrode. For the electric characterization, we deposited Ag circles on top of the heterostructures as top electrode. From XRD we found that the LCMO and YBCO layers grew textured aligned with substrate. The electrical properties with temperature measurements indicated the LCMO insulator behavior and the YBCO conduction at room temperature. I versus V curves at room temperature showed hysteretic behavior and the presence of two resistive states, whose electrical transport mechanism could be associated with space charge limited conduction (SCLC). The performed resistance switching with applied voltage tests indicate a dependence of the high resistance state (HRS)/ low resistance state (LRS) ratio with LCMO thicknesses. |
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T70.00358: Realizing Narrow Band Thermal Emitters in the Mid-Infrared by Utilizing Polaritonic Metasurfaces. Diego Garcia The purpose of this study is to show evidence that surface phonon polaritonic(SPhP) metasurfaces can produce a well-defined thermal emission signal in the optical phonon band of Silicon Carbide to realize narrow band emitters in the mid-IR wavelengths. Preliminary data and results have demonstrated strong localized SPhP resonances of these devices, so there is a high possibility that a well-defined emission signal will be obtained if we apply Kirchhoff’s Law of Heat Radiation. To observe the thermal radiation from the polaritonic metasurface patterns, an optical setup was built in which the beam path of the visible light and thermal radiation would be equivalent. This was done primarily for the precise alignment of the metasurface and to maximize the collection of thermal radiation. The device was heated conventionally and data analysis was attained using a FTIR Spectrometer. Initial results showed an emission spectrum with broad resonances from 820 cm-1 to 960 cm-1 and it was determined the resonances were from multiple patterns on the metasurface. Currently, we have improved the setup to collect emissions from single patterns. |
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T70.00359: Set of Techniques for High-Q Noble Metals Deposition: from Continous Ultrathin to Single-crystalline Films Aleksandr Baburin, Aidar R. Gabidullin, Dmitriy O. Moskalev, Evgeniy Lotkov, Michael Andronic, Anton I. Ivanov, Ilya A. Ryzhikov, Ilya A. Rodionov Losses are the most serious challenges, which impede high-Q plasmonic devices rapid development. There are numerous types of plasmonic devices with conflicting requirements for the films. One can conclude that most devices require continuous silver and gold films with ultra-low losses, extremely low roughness, single-crystalline structure and maximum possible surface plasmon polarition wave (SPP) propagation length on various substrates including amorphous. |
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T70.00360: Resistive switch on Iron oxides thin films Rafael Silva Gonçalves, ROMUALDO SANTOS SILVA JUNIOR, Petrucio Barrozo da Silva The resistive switch properties on binary oxides has largely studied due to the non-volatile properties and its potential to be used to develop data storage devices. The resistive switch has been attributed to the percolation of a conductor pathway across the insulator matrix. However, the properties of the growth of the conductor pathways and the speed of the switch between the different resistive states on iron oxide has not yet reports. In this work, we describe the mechanism of the resistive switch on the thin films of iron oxide growth by sputtering. The dynamics of growth of the conductor pathways in iron oxide and the speed of switch also will be reported. |
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T70.00361: Nanoscale Imaging Studies of Cobaltite Thin Films Using X-Ray Nanodiffraction Geoffery Ian Rippy, Lacey L Trinh, Alexander Michael Kane, Aleksey Ionin, Michael Steven Lee, Rajesh V Chopdekar, Dustin Gilbert, Alexander Grutter, Peyton Murray, Martin Holt, Zhonghou Cai, Kai Liu, Yayoi Takamura, Roopali Kukreja The perovskite (ABO3) and closely related brownmillerite (ABO2.5) phase of cobaltites possess a wide range of functional properties, which makes them promising candidates for solid oxide fuel cells, ionically-gated devices, and magneto-ionic devices. However, the role played by nanoscale morphology, i.e. phase separation and defects in these oxide thin films and heterostructures, remains unknown. This poster presents nanoscale imaging studies of emergent structural phases and their morphology in cobaltite heterostructures using x-ray nano-diffraction. Gd/La0.67Sr0.33CoO3 heterostructures were ionically and stoichiometrically controlled via the thickness of the Gd oxygen-gettering layers. Our measurements, using the hard x-ray nanoprobe at the Advanced Photon Source, show lateral and transverse nanoscale separation of the perovskite and brownmillerite phases. These nanoscale heterogeneities were characterized and strain mapped in real space with a spatial resolution of 25 nm. Our studies provide insights into the nanoscale morphology which can be utilized to tune the macroscopic functional properties of cobaltite heterostructures. |
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T70.00362: Steering on the high-temperature oxidation of Ru(0001) Haoran Chen Ruthenium oxide is the active phase and plays a signficant role in many catalytic reactions. By virtue of ultrahigh vacuum low temperature scanning tunneling microscopy, it has been observed that Ru(0001) could be oxidized to several novel kinds of ruthenium oxide films at different temperatures. High-resoltuion STM images showed that these films resulted from the novel structures formed at surface. Interestingly, these oxidation structures were inter-changeable upon reduction in hydrogen at different temperatures. After series of studies, the structual evolutions of Ru(0001) surface caused by high-temperature oxidation and reduction were revealed. |
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T70.00363: Chemical Reactivity at the Co/CuO interface Anil Chourasia The chemical reactivity at the Co/CuO interface has been investigated using the technique of x-ray photoelectron spectroscopy. Thin films of hafnium have been deposited on CuO substrates at room temperature by the e-beam method. The Oxford Applied Research EGN4 was used for this purpose. The spectral data in the hafnium 4f core level and copper 2p core level were investigated by XPS. The copper oxide was observed to get reduced to elemental copper while cobalt was observed to get oxidized to CoO. The thickness of the cobalt overlayer resulting in no chemical reactivity has been determined. The investigation was also performed at substrate temperatures of 100, 200, 300, 400, 500, and 600°C. The diffusion of copper through the overlayer was observed. The interface consists of a mixture of elemental cobalt, CoO and elemental copper. The amount of these materials is governed by the processing conditions. The results of the investigation will be presented. |
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T70.00364: Modeling of molecular stripe formation on insulating surfaces Christoph Schiel, Maximilian Vogtland, Angelika Kühnle, Philipp Maass We discuss theoretical approaches to model molecular stripe formation on dielectric surfaces as observed for 3-hydroxybenzoic acid (3-HBA) and 3-aminobenzoic acid (3-ABA) on calcite (104). For the self-assembly of the 3-HBA and 3-ABA molecules it is argued that adsorption-induced dipolar interactions cause an ordering towards a regular spacing between the molecular stripes. Measured stripe distance distributions show a good agreement with analytical results for a simplified one-dimensional model [1]. In this model scaling relations for the distance distribution are predicted that can be tested experimentally. In a refined approach, we further study the stripe formation on a two-dimensional lattice by an anisotropic Ising model with dipole-dipole interactions. For this model, stripe length and distance distributions as well as spatial correlation properties are determined by Monte Carlo simulations and compared with experimental data. |
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T70.00365: The Effect of Au Nanoparticles on the Photovoltaic Conversion Efficiency in CdTe/CdS Thin Films Yunis Yilmaz, Olivia Rodgers, Anthony J Viscovich, Ralph Nunez, Mehmet Alper Sahiner In our previous studies, we’ve worked on the effects silver nanoparticles have on the efficiency of CdS/CdTe thin film solar cells. In short, the addition of the nanoparticles in the np affects junction light scattering in a way that have a positive effect on efficiency of photovoltaic conversion. Currently, we’re testing gold nanoparticles on the same solar cells and plan on comparing the effects of different deposition times, particle sizes, and how they compare to the efficiencies of that of silver. The deposition method used to create these thin film solar cells is Pulsed Laser Deposition (PLD). The laser shoots at the target material we want to deposit (CdS/Au/CdTe) turning it into a plume of plasma that deposits onto a slide of ITO (indium tin oxide) coated glass. Varying how long the laser shoots at the gold changes the amount of gold deposited. The more gold in the np junction, the more light scattering happens, increasing the efficiency of the solar cell. However, the efficiency cuts off with enough gold added. The Au embedded CdS/CdTe thin film solar cells were characterized by XRD, AFM, SEM/EDX and the photovoltaic conversion efficiency were determined by Ketihley Sourcemeter setup. |
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T70.00366: Electrical and Physical Properties of Pulsed Laser Deposited Thin Films of YSZ Matthew Melfi, William E Cockerell, Erica Wiley, Kellen Murphy, Mehmet Alper Sahiner Solid Oxide Fuel Cells, SOFC’s, are devices that convert chemical energy from fuel into electricity from a series of electrochemical reactions. These fuels can be H2, CO, O2, etc. with a high efficiency of conversion. Comparing SOFC’s to coal power plants, the SOFC’S produce a higher electrical conversion efficiency. However, SOFC’s high temperatures create a lower ionic conductivity of the electrolytes. When decreasing the temperature, the ohmic resistance is increased hurting the performance. The method we are trying to take is decrease the ohmic resistance as a thin-film. An Yttria Stabilized Zirconia, YSZ, layer is produced from the fine dimple grain structure allowing high flow of oxygen ion mobility. The goal of our research is to optimize Pulsed Laser Deposition and determine the synthesis conditions which lead to minimum ohmic resistance in these films. We will also use different substrates and monitor the effect of the choice of the substrate on the YSZ thin-film properties. These thin-films will be characterized through electrical measurements such as 4 pt. probe resistivity measurements, Hall Effect, and structural and compositional characterization such as AFM, SEM, and EDX. |
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T70.00367: Structural stability and electronic levels of carbon-associated defects in SiO2: First-principles study Yu-ichiro Matsushita, Atsushi Oshiyama Silicon Carbide (SiC) attracts much attention as the power semiconductor materials due to its superior material properties such as wide-band gap and high breakdown electric field [1]. In spite of the great materials properties, SiC has a big issue to be solved. That is the low electron mobility of SiC-MOS(Metal-oxide semiconductor) devices caused by the high density of interface traps (Dit). In particular, carbon-associated defects staying around the SiC/SiO2 interface are the strong candidate for the Dit. In this study, we have clarified the structural stability and electronic levels of C-associated defects near the SiC/SiO2 interface on the basis of the density-functional theory (DFT). Consequently, we have found that near the SiC/SiO2 interfaces the carbon clustering is likely and some particular carbon defects cause defect levels near the conduction-band edge of SiC rendering them a strong candidate of the mobility killer. |
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T70.00368: Surface Morphology Studies of Strained and Oxygen Deficient Epitaxial Thin films of Strontium Titanate and Calcium Manganese Oxide Anton Wiggins, Azriel Weinreb, Francis Walz, Joseph Cartelli, David Houston, Bridget M Lawson, Jessica L Sizemore, Rajeswari M Kolagani, Gary Pennington, David Schaefer Calcium Manganese Oxide (CMO) and Strontium Titanate (STO) are technologically important materials for applications. Our recent work on epitaxial thin films of CMO have shown that films with a tensile lattice mismatch strain exhibit structural and electrical properties that indicate oxygen deficiency. Our Atomic Force Microscopy studies of CMO thin films reveal time dependent surface morphological changes accompanying oxygenation and de-oxygenation of the CMO films. AFM images indicate possible ordering of oxygen vacancies on the surface. Currently we are extending these studies to epitaxial thin films of STO to investigate strain-oxygen stoichiometry coupling. We will report the results of our systematic studies of the evolution of surface morphology with changes in the strain state and oxygen stoichiometry |
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T70.00369: Structural characterization of BaSnO3 thin films via x-ray scattering Claudia Lau, Youjung Kim, Kookrin Char, Charles H Ahn, Frederick J Walker The alkaline earth stannate BaSnO3 is a semiconductor with high carrier mobility at room-temperature when doped with La3+. BaSnO3 can be easily integrated with other perovskites for use in oxide electronic devices such as field effect transistors and sensors. We study the crystalline structure of BaSnO3 thin films grown on SrTiO3 substrates by pulsed laser deposition and molecular beam epitaxy via a variety of x-ray scattering techniques. With high intensity synchrotron scattering, we measure crystal truncation rods. Analysis of these rods yields information on structural distortions at the thin film surface and interface. We also measure rocking curves of BaSnO3 fundamental Bragg peaks for H+K+L=even and odd, where the intensity of the odd peaks are particularly sensitive to minute structural changes in the BaSnO3 film. These measurements have high accuracy, with a coefficient of variation within 5 percent for symmetrically identical peaks in the four quadrants of reciprocal space. We fit the integrated intensity of these fundamental even and odd peaks to a kinematic model of x-ray diffraction and determine parameters, including the Debye-Waller factor and the stoichiometry. |
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T70.00370: Computational study of the adsorption of bi-metallic clusters Nusaiba Zaman, Karima Lasri, Abdelkader Kara It was shown that small silver clusters can control the rate of LiO2 formation in Li-O2 batteries. The gap near the fermi energy was shown to control the oxygen reduction, an important reaction for LiO2 formation. Controlling the gap would ultimately control the rate of LiO2 formation. One can vary the size of the cluster to control the gap, however, this “knob” provides limited variance. Alloying, in combination with size variation offer a much wider control of the LiO2 formation. Here, we investigate the effect of Pd3M2 (where M varies from Ag, Au, Co, Cu, Mn, Ni, Pt, and Ru) clusters on the rate of O2 reduction at the hydroxylated alumina surface. Using DFT, we calculated the binding energies of these clusters on the alumina substrate which ranges from depending upon the composition of the alloy-cluster, its orientation and the adsorption site. We also find that Pd atom binds strongly with the substrate oxygen atom with a short bond-length of about 2.2 . We explore how the gap between the HOMO of the cluster and the Fermi energy of the system varies as a function of elemental composition. These preliminary results will open the door for more systematic studies of alloy clusters of different size and stoichiometry. |
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T70.00371: Development of Disordered and Ordered Nanoscale Terraced Topographies on Si Under Oblique Incidence Xe+ Ion Bombardment Emmett Randel, Carmen Susana Menoni, Richard M Bradley We explored disordered and ordered nanoscale terraced topographies that develop when a solid surface is bombarded by an ion beam at oblique incidence. It is shown that a flat Si surface when bombarded with 1500 eV Xe+ ions at 75° off normal incidence develops a disordered terraced topography. Using a Si surface pre-patterned with 500 nm pitch lines, it is demonstrated that ordered terraced topographies with sub-nanometer roughness on the facets develop under the above conditions. Ordered terraced substrates can be used in the fabrication of EUV multilayer blazed gratings. This work was performed in tandem with theory in an effort to refine models. |
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T70.00372: Graphene-oxide monolayers at the air-water interface Brent La Muro, Micah Vandersteen, Issam Ismail, Benjamin Stottrup Graphene-oxide is a novel material with tremendous applications to coatings and electronics. We utilize investigations of self-assembled GO monolayers at the air-water interface as the basis for experimental investigations in an undergraduate laboratory experience partnered with Augsburg University’s sophomore level Modern Physics course. A Langmuir trough with dual tensiometers oriented parallel and perpendicular to the barrier compression is used to measure the anisotropic forces during the compression and expansion of the monolayer. Investigations of size distribution and pH modulation of the aqueous subphase are presented here. Scanning electron microscopy of Langmuir-Blodgett deposited GO films provides a complementary look at GO morphology. Finally, we present the feasibility of GO studies at liquid-liquid interfaces. |
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T70.00373: Equating Cu(111) Stepped Surface and Nanoparticle Oxidation Energetics: A Multiscale Computational Study Matthew Curnan, Judith Yang, Wissam Saidi Understanding how to inhibit oxide formation on Cu interfaces is critical to corrosion prevention and catalyst deactivation. Oxide growth on metal surfaces is supplied by diffusing O atoms, such that anisotropy in O diffusion rates along different surface structures proportionally affects their observed growth. Structural defects, such as Cu(111) surface steps and similarly faceted nanoparticles (NPs), selectively oxidize with respect to adjacent flat surfaces and differently oriented defects. Previous research suggests that differences in defect atomic coordination, attributed to dangling surface Cu bonds, yield this selective oxidation. In this study, we confirm that these oxidation preferences are conserved over morphologically distinct, equivalently oriented, Cu(111) stepped surfaces and NPs with shared edge orientations. O diffusion energetics are calculated via density functional theory, cross-validated via reactive force field molecular mechanics, and reconciled with molecular dynamics simulations. Equating surface step and NP oxidation energetics furthers the understanding of how defect structure impacts selective oxidation. |
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T70.00374: Unconventional properties of superconductivity in SrTiO3/LaAlO3/SrTiO3 Yongsu Kwak, Jonghyun Song, Jinhee Kim The 2-Dimensional Electron Gases (2-DEGs) observed at the LaAlO3/SrTiO3 (LAO/STO) hetero-interface exhibits superconductivity, which has phase diagram as function of carrier density like high-temperature superconductor. However, the superconducting energy gap in LAO/STO has conventional superconductivity because the temperature dependence of superconducting energy gap follows Bardeen-Cooper-Schrieffer(BCS) theory. Here we report unconventional properties of superconductivity in STO/LAO/STO. We have fabricated vertical Josephson junction to measure the superconducting energy gap. We found that the superconducting energy gap estimated from the Andreev reflection of the Josephson junction did not follow BCS theory from the gap ratio, Δ/kBTC = 1.31. Additionally, we found evidence of unconventional superconductivity from the magnetic field dependence of superconducting critical current. It has opposite hysteresis, when it was compared with the hysteresis of magnetoresistance in STO/LAO/STO. |
(Author Not Attending)
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T70.00375: Ethylene Epoxidation on Ag(100), Ag(110), and Ag(111) - A First-principles and Kinetic Monte Carlo Study Matej Hus, Anders Hellman Ethylene epoxidation is commercially one of the most important selective oxidation reactions. Silver-based catalysts are the most common catalyst formulation in industry, albeit with significant doping. In this work, we present results from first-principles and kinetic Monte Carlo (kMC) modeling of the reaction on three pristine silver surfaces Ag(100), Ag(110), Ag(111), and on the missing-row reconstructed Ag(110). To better understand the kinetics on different surfaces and veraciously describe the surface coverages, we explicitly take into account the lateral interactions between the adsorbates and their effect on the activation barriers. Comparing with experimental data shows a good agreement with the modeling data especially for Ag(111) and somewhat worse for Ag(100). We show that Ag(100) offers better activity and activity than Ag(111). Differences in the active intermediates surface coverage were also studied. Furthermore, we studied the influence of alkali metals on selectivity. Our calculations show that the combination of electronegative Cl and electropositive Cs offers an optimal compromise between activity and selectivity. |
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T70.00376: Upgrading scanning tunneling microscopy with a radio-frequency modulation system for the detection of ferromagnetic resonance Hung-Hsiang Yang, Kanta Asakawa, Fumikazu Oguro, Yudai Sato, Susumu Takahashi, Yukio Hasegawa Scanning tunneling microscope (STM) usually provides us with only static information of material surfaces. Recently, however, dynamics of a single electron spin can be successfully detected by using STM through the resonance under the irradiation of radio-frequency wave [1]. |
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T70.00377: Carrier Dynamics and Ultrafast Zero-Bias Photocurrents in SnS2 Single Crystals Erin Morissette, Kateryna Kushnir, Alexis Buzzel, Curtis Doiron, Ronald Grimm, Lyubov Titova Moderate band gaps, high carrier mobility, and environmental stability make layered transition metal dichalcogenides attractive for optoelectronic and solar energy conversion applications. Of these materials, SnS2 demonstrates promise as a photocatalyst for visible light water splitting and in field-effect devices, with reported on-off current ratios >106 and carrier mobilities up to 230 cm2 V–1 s–1 [1,2]. Further progress in application of this emergent material requires the understanding of the dynamics of photoinjected carriers and optical excitations. |
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T70.00378: WITHDRAWN ABSTRACT
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T70.00379: Fluctuation Dynamics of Ferroelectric Nano-domains in BaTiO3 Thin Films Jianheng Li, Rahul Jangid, Geoffery Ian Rippy, Christopher Kohne, Arnoud Everhardt, Beatriz Noheda, Andrei Fleurasu, Sylvia Matzen, Roopali Kukreja Ferroelectric materials possess a thermodynamically stable polarization which can be controlled using temperature, voltage, and recently with optical pulses, enabling numerous device applications including non-volatile memories, actuators, and sensors. Ferroelectric domain structure plays an important role in manipulating polarization switching behavior and depends upon factors including strain, temperature and interfacial properties. In this study, we focused on understanding domain dynamics and fluctuations in BaTiO3 (BTO) thin films, which show ordered 90° alternating in-plane and out-of-plane domain from 50 °C to130 °C (Curie Temperature). We utilized X-ray photon correlation spectroscopy (XPCS) to probe domain fluctuations by accessing satellite peaks formed by ordered stripe domain in Bragg geometry. Our measurements show a two-step behavior, where from 50 °C to 90 °C, a slowing down of fluctuation timescales was observed due to stabilization of a/c domains. Above 90 °C, an increase in fluctuation timescales was observed as the material undergoes ferroelectric to paraelectric transition. This research demonstrates the characteristic behavior and timescales of nano-domain fluctuations in BTO thin films which have not been previously studied. |
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T70.00380: Intermetallic formation at deeply supercooled Ni/Al multilayer interfaces: a molecular dynamics study Peng Yi, Michael Falk, Timothy P. Weihs Reactions at interfaces between solids are critical processing steps for applications including microelectronics, coatings on turbine blades, and reactive materials. It is established experimentally that the first phase to form through an interfacial reaction need not be the most stable phase. Understanding the thermodynamics and kinetics of the solid-state reaction at interface is crucial for device engineering. |
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T70.00381: Evident effects of Hofstadter-type energy spectra of modulated bilayer graphene Danhong Huang, Andrii Iurov, Godfrey Gumbs, Liubov Zhemchuzhna When a uniform perpendicular magnetic field is applied to a graphene layer, a two-dimensional periodic scatter array only mixes the Landau levels from the same valley to form split electron-hole Hofstadter-type energy spectra. However, in the case of bilayer graphene, this periodic array is able to mix different sets of Landau levels originating from the two separate valleys. Such a valley mixing effect has been carefully investigated in this work using a projected model Hamiltonian which includes an interlayer effective mass, interlayer coupling and different on-site energies. The computed Hofstadter-type energy spectra and associated density-of-states are employed for further calculations of the ballistic conductance of electrons in bilayer graphene. |
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T70.00382: Valley splitting in a van der Waals heterostructure WSe2/CrI3: A first-principles study Zhiya Zhang, Xiaojuan Ni, Huaqing Huang, Lin Hu, Feng Liu
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T70.00383: Ion gating of the charge density wave order in two-dimensional NbSe2 Difei Zhang Recent experimental advances in atomically thin transition metal dichalcogenide (TMD) metals have unveiled a range of interesting phenomena including the coexistence of charge-density-wave (CDW) order and superconductivity down to the monolayer limit. The atomic thickness of two-dimensional (2D) TMD metals also opens up the possibility for control of these electronic phase transitions by electrostatic gating. Here, with the ionic liquid gate we tune the carrier density in 2D NbSe2 with the expectation to bring up a CDW phase, which is detailedly characterized with the Raman spectroscopy. We also investigate the variation of CDW order with the change in carrier density and complement phase diagram of 2D NbSe2, including CDW order and superconducting phase. |
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T70.00384: A first principle investigation on the surface properties of β-Ga2O3 with a focus on the stability mechanism and electronic characteristics: GGA and hybrid DFT studies Sajib Barman, Muhammad Nurul Huda β - Ga2O3 a transparent wide band gap semiconductor which has gained wide attention due to its suitability to a wide range of applications. Even though this is not a van der Waals material, it has shown that this material can be mechanically cleaved and exfoliated easily along favorable surfaces to make ultra-thin layers and used in device fabrications. One of the interesting properties of this material is that thin layers preserve the pristine bulk-like electronic properties, which makes it even more promising for applications in power devices. However, detail mechanism for such ultra-thin exfoliation is not known. Hence, a systematic study on the surface properties is essential. In this presentation, we have employed both GGA and HSE employed DFT to investigate surface properties. We are going to present our calculated surface stability, electronic band structures and electrons effective mass as a function of layer thickness for both (100)A and (100)B surfaces of this material. The understanding based on this study will provide a better control to fabricate thin film 2D devices. |
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T70.00385: Cross-plane thermal transport in SrRuO3 thin films investigated by time-domain thermoreflectance technique DoGyeom Jeong, Younggwan Choi, Hwiin Ju, Sungmin Woo, Woo Seok Choi, Jongseok Lee A SrRuO3 thin film has been widely used as a metal electrode in electronic devices based on transition metal oxides, and hence it is important to understand thermal transport properties through the SrRuO3 thin film to minimize a thermal degradation problem during the device operation. Using the time-domain thermoreflectance measurement technique, we investigate the cross-plane thermal conductivity of the SrRuO3 thin films with a thickness variation from 1 um to 8 nm. We find that the thermal conductivity becomes reduced from 5.0 W/m-K for the 1 um thick film to 0.94 W/m-K for the 8 nm thick film, and attribute such a large reduction of the thermal conductivity to the boundary scattering of thermal carriers, i.e., electron and phonon. In addition, we find a signature of the ballistic phonon transport at low temperature particularly when the film thickness becomes much smaller than the phonon mean free path. |
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T70.00386: Nonlinear optical responses of Rashba spin-split GeTe thin films Soon-Hee Park, Jeong Gi Choi, Chang Jae Roh, Seong Won Cho, Suyoun Lee, Jongseok Lee Ferroelectric alpha-phase germanium telluride (α-GeTe) has been known to have a giant Rashba spin split band, and hence can be a promising material for the spintronic application. We prepare α-GeTe thin films on a Si substrate with a thickness variation from 2 to 100 nm, and investigate their structural and electrodynamic properties by using second harmonic generation (SHG) and terahertz emission spectroscopy. From the azimuth-dependent anisotropy observed in the SHG responses, we find that all the films have a non-centrosymmetric crystal structure identified as a 3m point group. From the THz emission results, we demonstrate that a fairly strong built-in field exists at the film interface with the Si substrate. In particular, we observe a non-negligible helicity-dependence in the THz emission which can be a possible signature of a spin-polarized photocurrent arising from the spin-split Rashba bands. |
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T70.00387: METALS AND METALLIC ALLOYS
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T70.00388: Imaging magnetic and non-magnetic metal nanostructures using a field emission SEM. Stephen Blama, Mary Sajini Devadas An electron microscope can be used to image materials of nanoscale dimensions allowing for examination of size and shape characteristics, and chemical composition. We use an FEI Apreo scanning electron microscope to image magnetic (using electromagnetic mode) and nonmagnetic nanostructures (using electrostatic mode) of various metals (Au and Ag) and metal alloys (Fe/Co, Fe/Au) using different sample preparation methods, and varying system parameters for optimal image quality and resolution. Samples are prepared with spin coating followed by plasma cleaning, with controlled plasma composition. System parameters of spot size and accelerating voltage for different built-in detectors (ETD, EBSD, in-column BSD detectors, and STEM) are studied. Methods for obtaining optimal EDX maps are also investigated, as EDX is prone to sample charging and image drift due to extended exposure of the sample to the electron beam. Details of the imaging parameters and sample preparation for these nanostructures will be presented. |
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T70.00389: Dynamic behavior of carbon in steel by using soft X-ray absorption spectroscopy and spectrum simulation Kakeru Ninomiya, Kazutaka Kamitani, Yusuke Tamenori, Kazuki Tsuruta, Toshihiro Okajima, Daisuke Yoshimura, Hideaki Sawada, Keisuke Kinoshita, Maiko Nishibori The ferritic steel with supersaturated solid solution carbon remarkable increase in hardness by heat treatment (so-called aging) at low temperature. This has been considered to cause by the formation of the carbon cluster in ferritic steel.1 In this study, we aimed to understand the low temperature aging behavior of low-carbon steel focusing on carbon atoms, and the chemical state and local structural changes of carbon in low-carbon steel with aging were observed by soft X-ray absorption spectroscopy. Furthermore, we tried to clarify the structure of carbon cluster from the observed absorption spectrum by first principles calculation and spectrum simulation. As a result, we succeeded in clarifying the relationship between microscopic chemical state and macroscopic hardness change. Furthermore, it was found that the chemical state of carbon related to form carbon clusters changes dynamically in the early stage of heat treatment. The results of the spectral analyses suggested that solid solution carbon was interacted with the vacancies in bcc lattice. Therefore, it is suggested that vacancies may play an important role in the formation of carbon clusters. |
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T70.00390: Pseudo-conformal symmetry of a quantum charged particle in a mean zero static inhomogeneous magnetic field in two dimensions. Jonathan Miller The [non-canonical] stress-energy tensor for a quantum charged spinless particle in an inhomogeneous magnetic field of zero mean in two dimensions is quasi-conserved and symmetric. At zero energy it is also traceless, but this continuum, non-interacting chiral (Arovas-Zhang) model is not conformally invariant. Rather, it is pseudo-conformally invariant, a la Bers' pseudo-analytic functions, reflecting a certain local anisotropy. There are two locally conserved currents; one of them is novel, and its generator is elucidated; the corresponding symmetry is broken by potential disorder. Certain of these properties are shared by a classical diffusing particle in a quenched random vorticity field. |
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T70.00391: Studying the correlations and solubility of hydrogen in niobium using Density Functional Theory calculations Arvind Ramachandran, Houlong Zhuang, Klaus S Lackner In this work, we present a Density Functional Theory (DFT) study of hydrogen correlations and solubility in niobium. Finding the preferred interstitial site for single hydrogen atoms, calculating the pair-wise hydrogen correlations, and the treatment of many hydrogen atoms in a niobium cell are parts of this work. By studying how the pair-wise hydrogen-hydrogen interaction energy varies as a function of their distance, we develop the theoretical counterpart of the empirical Westlake criterion, a rule that states that hydrogen atoms cannot simultaneously occupy pairs of interstitial sites closer than 0.21 nm. Based on this inference, we provide a systematic way of populating many (>3) hydrogens in the niobium lattice. Using the differential binding energies and vibrational frequencies of dissolved hydrogens at varying hydrogen concentrations, we estimate the solubility of hydrogen in niobium. Apart from the conventional way of calculating the entropy of interstitial hydrogens under the harmonic oscillator approximation, this work includes a new approximation that treats the hydrogens as a monatomic ideal gas. The solubility predictions are in good agreement with experimental data. |
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T70.00392: Unraveling the Histone Replacement Pathway in Sperm Ruth Mosunmade In somatic cells, DNA is wrapped around histone octamers in order to form a chromatin structure that is packed inside the nucleus. However, during human spermatogenesis approximately 85-90% of the histones in the DNA are replaced by an arginine rich protein called protamine. This allows for more efficient packaging of the DNA in the sperm cell. As a result, the sperm cell's movement is more hydrodynamic and the genetic material is protected. In this study we aim to understand the mechanics of DNA condensation in the nucleus of sperm cells. More specifically, we are interested in reconstructing the direct histone-protamine replacement pathway that occurs in fish. To study this phenomenon, we utilize a Tether Particle Motion (TPM) assay. In the TPM assay, a single DNA molecule is attached to a 1 μm "polystyrene bead on one end and is attached to a glass coverslip on the other. Using video microscopy, we track the motion of the bead and measure the length of the tether over time. When histones are replaced by protamine, we expect a change in the standard deviation of the DNA tether's movement due to further DNA compaction. Understanding this pathway has implications in biomaterial, epigenetic, and fertility research. |
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T70.00393: Creating a viscoelastic spectrum of aqueous polyacrylamide gel at varying concentrations Michelle Ash, Gopal Verma, Jean-Pierre Delville Current methods to obtain microrheological measurements inside liquid materials hold the problem of contaminating samples with an internalized foreign particle, especially problematic for intracellular microrheological measurements. Optical interferometry solves this problem by allowing for pico- and nanoscale rheological measurements without coming into contact with the interior system of a sample. Aqueous polyacrylamide (PAAm), a non-Newtonian gel can be used as a model of a cell, mirroring the experimental setup needed to study cellular systems. With a simple setup, a high-power green pump laser is incident on a PAAm droplet, inducing droplet height deformation via radiation pressure, then detected by interferometry using a low-power red probe laser. Firing a pump laser pulse deforms the gel droplet height between maxima and minima, from which the viscosity is calculated. Comparison of our experimental viscoelastic data of PAAm at a single pulse and varying frequencies to literature values confirms an accurate viscoelastic spectrum of PAAm. Based on our measurements and the noninvasiveness of this technique, mechanical perturbation of a gel surface demonstrates possibility of replication for cellular measurements. |
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T70.00394: Detection of out-of-time-order correlators and information scrambling in cold atoms Ceren Dag, Luming Duan We propose a disordered ladder spin model which can be designed in a scalable cold atom setup at the hard-core boson limit to dynamically detect out-of-time order correlators (OTOC) and hence information scrambling. Our protocol utilizes the Hamiltonian sign reversal for the evolution backward in time by applying single spin gates successively. We study different limits of disordered Ladder-XY model with focusing on its OTOC behavior and level statistics. We show that in its chaotic limit, disordered ladder-XY model decays exponentially in early-time with power-law tails before its scrambling time and it demonstrates a range of lightcones due to local spin-spin interactions. Based on our results, one can observe how the ladder systems could be useful to understand and experiment information scrambling in the transition from well-studied 1D models to unexplored 2D models. |
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