Bulletin of the American Physical Society
Joint Fall 2017 Meeting of the Texas Section of the APS, Texas Section of the AAPT, and Zone 13 of the Society of Physics Students
Volume 62, Number 16
Friday–Saturday, October 20–21, 2017; The University of Texas at Dallas, Richardson, Texas
Session B4: Condensed Matter Physics I |
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Chair: Mark Lee, University of Texas at Dallas Room: DGAC 1.128 |
Friday, October 20, 2017 2:45PM - 2:57PM |
B4.00001: An Alternative model of Spin-Dependent Double Well Lattice for Ultra-Cold Atoms Xiaohe Zhou The theory of Bose-Einstein Condensation has been a widely studied issue since first proposed in 1924. However, most of its predictions are lacking in experimental verification. Not until 2009, a group from NIST conducted an experiment which created a synthetic magnetic field in solids where neutral atoms behaves like charged atoms. Their experiment provides a brand new perspective of studying condensed matter systems. This talk will consist two parts. First is a brief review of background knowledge: Starting from the NIST's experiment, fundamentals covering Raman laser, Bose-Hubbard Model as well as SSH chain are introduced; Then the second half, the talk will mainly based on my undergraduate project. Instead of the widely studied double well lattice model, I did a mathematical transformation to the lattice Hamiltonian in order to get an effective single well lattice model under external field. There are correspondences and certain simplicities merge comparing to the original lattice model. Phase transition under half-filling situation would serve as example for simplicity. In addition, common terminologies used in my work like mean-field theory and quantum phase transformation are introduced. [Preview Abstract] |
Friday, October 20, 2017 2:57PM - 3:09PM |
B4.00002: Stability enhancement of solar absorber material Cu$_{\mathrm{2}}$S by alloying: A DFT study Sajib Barman, Muhammad Huda Cu$_{\mathrm{2}}$S is an important solar absorber material, which has already proved its potential in the field of renewable energy. Despite having all other important properties and being earth abundant and non-toxic, it suffers from spontaneous Cu vacancy formation, which eventually makes the material to behave as a degenerate semiconductor due to high p-type doping. As a result, the stability of the material decreases, and constricts its usages in the field of renewable energy. A relatively new phase of Cu$_{\mathrm{2}}$S, named as acanthite-like phase is found preferable than the well-known low chalcocite phase. However, the Cu vacancy formation tendency has not improved much. We have found that alloying Ag with this new acanthite-like phase can help to reduce the vacancy formation tendency and to control the Cu atoms diffusion in the crystal. Here, we present a systematic approach within density functional theory framework to stabilize this material toward its suitable use as a renewable energy material. [Preview Abstract] |
Friday, October 20, 2017 3:09PM - 3:21PM |
B4.00003: First-Principles Study of the Structural, Vibrational and Thermal Properties of Some Type II Tin-Based Clathrates Hadeel Zahid, Dong Xue, Charley Myles In addition to the $\alpha $-Sn and $\beta $-Sn crystal structures, Sn can crystallize in the clathrate structures. These contain 20, 24, or 28-atom ``cages'' which allow the introduction of loosely bound guest atoms. Due to their low thermal conductivity, some of the Sn-based materials are of interest because as possible thermoelectric materials. Here, we report the results of a systematic, first principles, computational study of the properties of some type II Sn-based clathrate materials. This study was motivated by a recent computational study [1] of the properties of the Type-II clathrate compounds A$_{\mathrm{x}}$Si$_{\mathrm{136}}$ and A$_{\mathrm{x}}$Ge$_{\mathrm{136}}$ (A$=$Na, K, Rb, Cs; 0$\le $x$\le $24), which increased the understanding of the role of the guest atoms and their composition x in determining the properties of the clathrate materials. Our calculations are based on density functional theory and utilize the VASP code. We present results for the structural, vibrational, and thermal properties of the Type II clathrates Sn$_{\mathrm{136,\thinspace }}$and A$_{\mathrm{x}}$Sn$_{\mathrm{136}}$ (A $=$ Na, K, Cs; x $=$ 8, 16, 24). Our predictions include lattice parameters, elastic constants, sound velocities, vibrational modes, and thermal properties. The predicted dependences of these properties both on the guest atom composition x and on the choice of guest atom are discussed. [1] D. Xue, C. Myles, C. Higgins; Materials 2016, \textbf{9}(8), 691. [Preview Abstract] |
Friday, October 20, 2017 3:21PM - 3:33PM |
B4.00004: Landau levels of bilayer transition metal dichalcogenides Peng Peng Zheng, Fan Zhang The quantum binary system at low temperature is not limited to only spin, but that of valley and layer degrees of freedom as well. A prime example is bilayer transition metal dichalcogenide (TMD). Here we examine the Landau level structure of bilayer TMD. We show how the interlayer electric field and the magnetic Zeeman field couple and control the layer and valley pseudospins, respectively, thereby tuning the Landau levels. Our results shed a new light on the quantum Hall effects of atomically thin TMD's. [Preview Abstract] |
Friday, October 20, 2017 3:33PM - 3:45PM |
B4.00005: Fractional Fluxon dynamics in Long Josephson Junctions Lawrence Rhoads, Van Mayes, Ju Kim, Ram Shoham Fluxons are promising candidates for qubits in superconducting quantum computers. Fluxons are quantized loops of magnetic flux found in long Josephson Junctions. These fluxons arise due to the time reversal symmetry breaking in a long Josephson junction (LJJ) with two-band superconductors. The spatial dependence of the critical current density can generate magnetic flux in the insulator layer, creating two fractional fluxons. The interaction between the them is repulsive at short distances, but attractive at long distances, causing the formation of a fractional fluxon bound pair. An investigation of the dynamics of this pair as a function of various parameters is presented. The separation distance between fluxons as a function of bias current, the observability of each fluxon, and Macroscopic Quantum Tunneling (MQT) behavior through a barrier are examined. [Preview Abstract] |
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