Bulletin of the American Physical Society
2018 Joint Fall Meeting of the Texas Sections of APS, AAPT and Zone 13 of the SPS
Volume 63, Number 18
Friday–Saturday, October 19–20, 2018; University of Houston, Houston, Texas
Session P05: Condensed Matter Physics II |
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Chair: Alex Zakhidov, Texas State University Room: Science and Engineering Classroom (SEC) 204 |
Saturday, October 20, 2018 2:10PM - 2:22PM |
P05.00001: Methods for Dynamical Simulations in Advanced Materials Michael R Tagaras, Roland E Allen This talk will cover several methods for dynamical simulations of advanced materials, including ultrafast phase transitions. In our first method, Ginzburg-Landau-like order parameters are coupled to each other and to the vector potential of an incoming laser pulse, so that the resulting phase transition is described by time-dependent Ginzburg-Landau theory. This approach is capable of describing one mechanism which is observed experimentally in light-induced superconductivity. A method will be introduced for treating ultrafast phase transitions, such as those involving superconductivity, magnetism, charge density waves, and spin density waves. Results will be presented for a toy model, with the electronic temperature immediately after the laser pulse calculated as a function of the fluence. Finally, we improve on this approach with the addition of an electronic self-energy, which allows for calculations currently not possible with conventional density-functional-based methods. |
Saturday, October 20, 2018 2:22PM - 2:34PM |
P05.00002: Study of High-Pressure Effects on Weyl Semimetal Mo0.25W0.75Te2 Rabin Dahal, Liangzi Deng, Narayan Poudel, Melissa Gooch, Zheng Wu, Ching-Wu Chu Transition metal dichalcogenides MoxW1-xTe2 have attracted great research interest since they exhibit the Weyl fermion semimetal state with x = 0.25, offering the possibility to realize a tunable Weyl semimetal [1]. Weyl semimetals show different interesting properties, including negative longitudinal magnetoresistance, quantum anomalous Hall effect, and unconventional superconductivity. Single crystals of Mo0.25W0.75Te2 with length up to 1.1 cm were grown via chemical vapor transport method and characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, and transport measurements. High pressure effects have been investigated by using a homemade BeCu clamp cell. A possible structural transition was observed under pressure at and above 1.2 GPa, but the signature of superconductivity in Mo0.25W0.75Te2 at temperature down to 1.3 K and under pressure up to 1.7 GPa was not detected. High pressure studies above 1.7 GPa using a diamond anvil cell are in progress. [1] Belopolski, I. et al., Nat. Commun. 7, 13643 (2016). |
Saturday, October 20, 2018 2:34PM - 2:46PM |
P05.00003: A Newtonian Electron Model James Charles Espinosa When J.J. Thompson discovered the electron, numerous physicists like Lorentz, Abraham, and Poincare tried to create a model for it. Their charge distributions succeeded answering many questions: the origin of inertia, the gyromagnetic ratio, and the intrinsic magnetic moment. Their ideas were forestalled by the seemingly insurmountable problem of instability. A non-electromagnetic force was postulated by Poincare to keep the like charges from tearing themselves apart, eliminating the possibility of a purely electromagnetic theory of matter. We believe that any field theory will suffer from this problem. After reviewing Oppenheimer’s proof of the instability of any charge and current distribution obeying the Maxwell Lorentz equations, we will show how an action at a distance theory such as Ritz’s force law can give us a stable charge and current distribution without Poincare’s stress. Our preliminary results preserve the initial successes of the early pioneers and suggest further directions of research. |
Saturday, October 20, 2018 2:46PM - 2:58PM |
P05.00004: Search for Higher Tc Superconductors via Interface Mechanism and High Pressure Liangzi Deng, Hanming Yuan, Shuyuan Huyan, Luke Kelly, Rabin Dahal, Samira Daneshmandi, Moein Adnani, Zheng Wu, Melissa Gooch, Yanfeng Lyu, Hungcheng Wu, Paul Chu Since the discovery of superconductivity in 1911, researchers have continued the search for superconductors with higher transition temperatures (Tc). Many strides have been made with the increase of the Tc, as can been seen from the evolution of record Tc over time. We believe a holistic multidisciplinary enlightened empirical approach can be most fruitful. Two paths have been adopted to raise Tc: to realize novel mechanism inspired by the theoretical models and to discover new compounds guided by experience and insight empirically. Over the last few years, we discovered nonbulk superconductivity in rare-earth doped CaFe2As2 (Ca122) with an onset Tc of 49 K, which is higher than the Tc of any known compounds formed of the constituent elements at ambient or under high pressures. We successfully induced superconductivity with a Tc of 25 K in the mixed phase region of two non-superconducting phases in undoped Ca122. We also observed a universal increase of Tc under high pressure in BSCCO. Our systematical studies in R-doped Ca122 and undoped Ca122 both suggest that the observations may be attributed to an interface-induced Tc and our investigation on BSCCO reveals that ultra-high pressure may help to break away from the predictions by the rigid band model and reach even higher Tcs. |
Saturday, October 20, 2018 2:58PM - 3:10PM |
P05.00005: Superconductivity in epitaxial La2-xPtxSi films Jian Liao, Yunbo Ou, Jagadeesh Moodera, Xiaoyan Shi In noncentrosymmetric superconductors, by doping with heavy-elements, the absence of inversion symmetry and presence of parity-violating antisymmetric spin-orbit coupling may lead to admixture of spin-singlet and spin-triplet components. We investigated the transport properties of various La2-xPtxSi thin films grown by molecular beam epitaxy (MBE). The Pt doping suppresses transition temperatures, and tunes the charge carrier types and densities dramatically. Interestingly, the magnetoresistance shows a two-step transition at finite temperatures below Tc. Furthermore, the differential resistance measurement reveals complex superconducting gap structures in magnetic fields up to 1 T. These features indicate the competing orders in the materials. |
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