Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session D3: Condensed Matter Physics II |
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Chair: Michel Pleimling, University of Virginia Room: Monroe Room |
Thursday, November 10, 2016 3:45PM - 3:57PM |
D3.00001: Impurity Solubility in Zn II-VI Semiconductors D.A. Barlow The maximum n doping level in certain Zn II-VI semiconductors (ZnTe, ZnSe, ZnS, ZnO) is seemingly correlated with other properties of these solids. These include heats of formation, electronegativity differences, covalent radii, p-d repulsion energy and bond strengths. It has been suggested that the maximum attainable carrier concentrations in theses compounds is limited possibly due to the formation of certain vacancy and vacancy complexes which act to compensate carriers. However, recent reports indicate that the concentration of these defects in the solid are insufficient to explain doping limitations. We show here that the solubility of an anion dopant in the anion sub-lattice can be used as a guide to predict the ultimate maximum achievable n doping level in the above compounds. A standard statistical mechanical model which requires a formation energy is utilized to demonstrate this. This energy is then estimated using reported bond strengths for the binaries involved. The results suggest that dopant solubility is the determining factor for achieving maximum n doping in these materials. [Preview Abstract] |
Thursday, November 10, 2016 3:57PM - 4:09PM |
D3.00002: Computational Analysis of Magnetic Molecules Jared Singleton, Larry Engelhardt A ``magnetic molecule'' is a cluster of both magnetic and non-magnetic atoms, where the non-magnetic atoms serve to isolate the magnetic core of a magnetic molecule from any neighboring molecules. This makes the intermolecular interactions between the magnetic sites negligible, such that the analysis of a macroscopic collection of these molecules can yield properties about a single magnetic molecule. For my analysis, the parameters of two magnetic molecules, Cr8Gd8 and Ni21Gd20, were determined by matching predictions of theoretical models to experimentally measured data. To simulate the molecules in a magnetic field, the Heisenberg model was used. The results were obtained through computations using a quantum Monte Carlo algorithm from the ALPS library. Multiple thermodynamic properties were analyzed to determine the strength of the intramolecular bonds, the gyromagnetic ratio, and the anisotropy. The thermodynamic properties that were used included the magnetic susceptibility, magnetization, and heat capacity, where the heat capacity was integrated over the temperature range to determine the change in entropy. [Preview Abstract] |
Thursday, November 10, 2016 4:09PM - 4:21PM |
D3.00003: Low temperature TE properties of BiSb with magnetic field Sheng Gao, Joesph Poon Thermoelectric (TE) technology plays an important role in converting the currently under-utilized thermal energy directly into electrical power from renewable and waste heat sources in an environmentally friendly manner. Recently, the study on high efficiency TE materials draws attentions of many research groups. Among different TE materials, solid solution alloy of BiSb, as known as the first topological insulator, has one of the best TE performance at low temperature range (20K\textasciitilde 220K). Starting from adding 7{\%} Sb, the semi-metallic bismuth will lose its overlapping between valence band and conduction band and becomes a narrow gap semi-conductor up to 22{\%} Sb. What's more, large enhancement in thermal power of BiSb in magnetic fields was observed, which can be explained based on the transverse-transverse thermo-galvanomagnetic effects. In our research, we studied the segregation effect which strongly affects the sample homogeneity and also built models to describe magneto-Seebeck and magneto-resistivity of BiSb, which could be a hopeful way to pursue higher TE performance. [Preview Abstract] |
Thursday, November 10, 2016 4:21PM - 4:33PM |
D3.00004: Positively Charged Muonium Diffusion in In$_{\mathrm{2}}$O$_{\mathrm{3}}$ Brittany Baker, Roger Lichti, Patrick Mengyan, Gurkan Celebi Indium oxide (In$_{\mathrm{2}}$O$_{\mathrm{3}})$ is a transparent conducting oxide (TCO) commonly found in mixtures used as windows and transparent electrodes in optical semiconductor devices (i.e. LEDs and solar cells). Hydrogen diffusion in the TCO layer and across the interface between the TCO and the semiconductor device plays an important role in the degradation of the transparency of TCO windows or electrodes. Theoretical calculations show positive H as the only stable, interstitial H charge state above the neutral H ionization temperature. Muon Spin Relaxation measurements were performed to investigate positive muonium (Mu$^{\mathrm{+}})$ diffusion which are an experimentally accessible analog to H$^{\mathrm{+}}$. Three distinct Mu$^{\mathrm{+}}$ states are identified between 2 K and 1000 K; a static low temperature state, a dynamic state above room temperature, and a trapping state from 400 K to 800 K. The trap component creates complex dynamics and has been modeled assuming the Mu$^{\mathrm{+}}$ transfers between the dynamic state and the trapping state. Fits of the model to the data provide information about capture and release rates and energy barriers into and out of the trap state. Here we present and discuss results from these fits, possible site locations for each state and likely diffusion paths. [Preview Abstract] |
Thursday, November 10, 2016 4:33PM - 4:45PM |
D3.00005: Strain induced enhancement of magnetoresistance in Weyl semimetal MoTe$_{\mathrm{2}}$. Junjie Yang, Despina Louca Recently MoTe$_{\mathrm{2}}$ that belongs to the type II Weyl semimetals, has attracted considerable attentions because of its intriguing topological physics as well as its potential applications in information technology. For instance, an extremely large magnetoresistance (MR) that is crucial for either sensitive magnetic sensors or the basic elements in magnetic random access memories, has been observed in \quad MoTe$_{\mathrm{2}}$. More interestingly, it was also found that external pressure can dramatically enhance its superconducting transition temperature. Strain is another novel method to tune the physical properties of materials. Tuning the physical properties of Weyl semimetal by strain has not been reported to date. Here, we present the evidence from an electric transport experiment on a single crystal MoTe$_{\mathrm{2}}$, that the strain can significantly enhance the MR by around 28{\%}. From the measurements, we observed that the enhancement of MR induced by strain increases with decreasing temperature and also increases with increasing magnetic field. It reaches a maximum value of 28{\%} at 2 K at 9 T. The observed strain induced enhancement of MR in MoTe$_{\mathrm{2}}$ provides insights into the interplay between strain and the topological physics. [Preview Abstract] |
Thursday, November 10, 2016 4:45PM - 4:57PM |
D3.00006: Development of a Gas Plasma-Based THz Time-Domain Spectrometer for the 25 T Split Florida Helix Magnet System A.D. Burch, J.A. Curtis, A.G. Linn, B. Barman, M. Stiles, J.L. Reno, S.A. McGill, D. Karaiskaj, D.J. Hilton THz time-domain spectroscopy has been widely used to study two dimensional electron and hole gas systems.$^{\mathrm{1,2}}$ In order to extend the magnetic field range of these measurements we have developed a gas plasma-based THz time--domain spectrometer (TTDS) for use in the 25 T Florida Split Helix magnet system at the National High Magnetic Field Laboratory (NHMFL) at Florida State University. We have successfully quadrupled the bandwidth compared to traditional THz spectrometers (approx. 0.1-2.5 THz) based on non-linear crystals. We have recently performed the first high magnetic field TTDS measurements on a high mobility two dimensional electron gas sample. $^{\mathrm{1}}$Curtis, J. A.\textit{ et al.}, Physical Review B 2016, 93 (15), 155437. $^{\mathrm{2}}$Kamaraju, N.\textit{ et al.}, Applied Physics Letters 2015, 106 (3), 031902. [Preview Abstract] |
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