Bulletin of the American Physical Society
86th Annual Meeting of the APS Southeastern Section
Volume 64, Number 19
Thursday–Saturday, November 7–9, 2019; Wrightsville Beach, North Carolina
Session J03: Condensed Matter III |
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Chair: Zhiling Dun, Georgia Tech Room: Holiday Inn Resort Turtlewatch |
Saturday, November 9, 2019 10:30AM - 10:42AM |
J03.00001: Strain Engineering of the Electronic and Phonon properties of Lanthanum Monopnictides Chia-Min Lin, WEI-CHIH CHEN, Cheng-Chien Chen Rare-earth monopnictides have attracted significant attention due to their exotic electronic and topological properties with potential thermoelectric and spintronic applications. Here, we theoretically investigate strain effects on lanthanum monopnictides LaX (X $=$ N, P, As, Sb, and Bi) by first-principles simulations using hybrid density functionals with spin-orbit coupling. In particular, the phonon properties, electronic bandstructures, and topological natures of these materials under compressive and tensile strains are computed. It is shown that strain engineering is an effective approach to manipulate the properties of LaX for improved performance and device applications. [Preview Abstract] |
Saturday, November 9, 2019 10:42AM - 10:54AM |
J03.00002: Search for Hysteresis in Longitudinal and Transverse Voltage in Superconducting Films Phillip Broussard, Anna Spencer The claim by Glazman (Sov. J. Low Temp. Phys. {\bf 12}(7), 1986) of hysteresis in Transverse Voltage (TV) as an indication of TV being due to Vortex-Anitvortex annihlilation has inspired us to search for such hysteresis. Though we have looked at TV previously, in that case we could only look at hysteresis in the TV and the sweep rate of the current was asymmetric. We have now improved our apparatus to have symmetric sweep rates for current up as well as down, and now we can examine both the TV and the longitudinal voltage (LV) as a function of the sweep rate. Films of niobium, niobium zirconium alloy, and niobium nitride have been examined. Hysteresis is observed in all films, both in TV and LV signals. The hysteresis increases as the temperature of the films are lowered below $T_{c}$ and as the frequency ($f$) of the sweep increases. We see evidence of a $\sqrt{f}$ dependence to the hysteresis, which is inconsistent with a thermal hysteresis explanation. [Preview Abstract] |
Saturday, November 9, 2019 10:54AM - 11:06AM |
J03.00003: Ordering in magnetic skyrmion lattices James Stidham, Michel Pleimling Ordering in magnetic skyrmion lattices is an active area of research for skyrmion systems. In this talk, we present recent results obtained using Langevin molecular dynamic simulations, based on a previously derived particle model of skyrmions. Using a Voronoi cell algorithm, we examine the effect of the Magnus force present in skyrmion systems and how it affects ordering when noise is both present and absent in the system. We observe power-law behavior during late time ordering in these skyrmion systems. We also find power-law behavior when looking at the difference in time of consecutive events as the system orders. [Preview Abstract] |
Saturday, November 9, 2019 11:06AM - 11:18AM |
J03.00004: Effects of Supercurrent on the Higgs mode in Superconductors Ankit Kumar, Alexander Kemper When a superconducting order is perturbed, one of the resulting excitations gives rise to the amplitude oscillation mode known as the Higgs mode. The existence of the Higgs mode in a perturbed broken-symmetry state is one of the fundamental phenomena in condensed matter systems. However, the Higgs mode is hard to measure experimentally due to its spin-less and charge-less nature. Recently, it was proposed that the Higgs mode in superconductors can be coupled to light in the linear regime if there is a non-zero supercurrent present in the system. Motivated by that, we study the dynamics of the Higgs mode in the presence of supercurrent. We find that the supercurrent creates an asymmetry of the electron distribution in the momentum space which leads to a momentum-dependent superconducting spectral gap. When we pump the system with an ultra-fast light pulse, the frequency of the Higgs mode gains momentum dependence. We analyze the dynamics of the Higgs mode through the electron spectral function which can be measured using angle-resolved photoemission spectroscopy (ARPES), and propose that the presence of supercurrent may help in the observation of the Higgs mode through time-resolved ARPES. [Preview Abstract] |
Saturday, November 9, 2019 11:18AM - 11:30AM |
J03.00005: Detecting magnetization dynamics with atomic defects in diamonds Aron Guerrero, Pasquale Ferraro, H.J. Jason Liu Progress in current technology can be attributed to scaling down internal components, such as magnetic devices. One type of magnetic device, known as a magnonic device, uses magnetic excitations, or spin waves, to transfer information. As these devices are reduced in physical size, current magnetic field detection methods are unable to accurately measure the small magnetic fields produced by the spin waves. Recent studies in the atomic defects in diamonds have shown that the photoluminescent characteristics of these defects can be used to detect fields as small as 3 nT. The defect, known as a nitrogen-vacancy (NV) center, contains a spin-1 electronic system which emits red photons when excited by a green laser. The spin system is also degenerate at microwave energies through Zeeman splitting. The difference in the microwave energies is proportional to the external field that the NV center senses. In this talk, I will discuss the process in which we use a custom confocal microscope to collect the red photons emitted by the NV center in order to determine the magnetic field created by the spin waves in magnetic nanostructures. [Preview Abstract] |
Saturday, November 9, 2019 11:30AM - 11:42AM |
J03.00006: Non-Equilibrium Study of Superconductivity in Extended Hubbard Model Wei-Chih Chen, Yao Wang, Cheng-Chien Chen Photo-induced phase transitions have been demonstrated in pump-probe experiments on several strongly correlated systems. Here, we study various order parameters including charge ordering, spin ordering, and superconducting pairings in the extended Hubbard model by large-scale exact diagonalization. The equilibrium phase diagrams with different carrier fillings will be shown and compared with previous studies based on mean-field and functional renormalization group methods. Using the equilibrium ground state as the initial state, we then study the non-equilibrium dynamics of the aforementioned order parameters in the presence of an oscillatory Gaussian light pulse. We fully investigate the effects of light polarization, frequency, amplitude, and width on different order parameters. It is shown that light-polarization control can be a promising new approach to enhance or suppress superconductivity of desired pairing symmetry. [Preview Abstract] |
Saturday, November 9, 2019 11:42AM - 12:12PM |
J03.00007: Ultrafast topological resonances in transition metal dichalcogenide monolayers Invited Speaker: S. Azar Oliaei Motlagh We predict that a single cycle of a circularly polarized intense laser pulse populates the conduction band of the monolayer of transition metal dichalcogenides and induces ultrafast and strong valley polarization. This induced valley polarization is a result of ultrafast topological resonances, which occur when the topological (geometrical) phase and dynamic phase cancel out each other. The topological resonance, a nonlinear phenomenon independent of the electron spin, is manifested in materials with hexagonal lattice and broken inversion symmetry. [Preview Abstract] |
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