Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S08: Transport, Optical, and Thermodynamic Phenomena 
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Sponsoring Units: DCMP Chair: Heng Guo, UESTC China Room: LACC 153C 
Thursday, March 8, 2018 11:15AM  11:27AM 
S08.00001: LandauZener tunneling problem for particles in periodic lattice Ryuji Takahashi , Naoyuki Sugimoto The LandauZener (LZ) problem plays an important role for the tunneling in nanoscale systems. Conventionally, the LZ formula is widely used for the calculation of the tunneling probability, and this formula is obtained by a linear approximation in the vicinity of the band edges for periodic lattice systems. Therefore, when we take into account the nonlinear effect by the periodic lattice, it is not sufficient for the calculation of the tunneling probability by the LZ formula. In this presentation, we report the LZ tunneling problem for particles bound in the periodic lattice [1]. To this end, we construct the path integral based on the Bloch and Wannier functions in the presence with an external force, and the transition probability is calculated for the SuSchriefferHeeger model with a constant gap. Then, we find that the tunneling probability becomes drastically larger than that by the LZ formula. This enhancement is prominent for small values of the external field or small hopping integral, and comes from the difference between the Dirac and the periodic dispersions. [1] Ryuji Takahashi and Naoyuki Sugimoto, Phys. Rev. B 95, 224302(2017). 
Thursday, March 8, 2018 11:27AM  11:39AM 
S08.00002: The Berry curvature dipole and dc photocurent in Weyl semimetal material Yang Zhang , Yan Sun , Claudia Felser , Jeroen Van den Brink , Binghai Yan Noncentrosymmetric metals are anticipated to exhibit a dc photocurrent in the nonlinear optical response caused by the Berry curvature dipole in momentum space. Weyl semimetals (WSMs) are expected to be excellent candidates for observing these nonlinear effects because they carry a large Berry curvature concentrated in small regions, i.e., near the Weyl points. We have implemented the semiclassical Berry curvature dipole formalism into an ab initio scheme and investigated the secondorder nonlinear response for two representative groups of materials: the TaAsfamily typeI WSMs and MoTe2family typeII WSMs. Both types of WSMs exhibited a Berry curvature dipole, in which typeII Weyl points are usually superior to the typeI because of the strong tilt. Corresponding nonlinear susceptibilities in several materials promise a nonlinear Hall effect in the dc field limit, which is within the experimentally detectable range. 
Thursday, March 8, 2018 11:39AM  11:51AM 
S08.00003: Shift current driven by ultrashort light pulses in insulating and metallic inversion asymmetric systems: Timedependent nonequilibrium Green's function approach Utkarsh Bajpai , Bogdan Popescu , Branislav Nikolic , Hiroaki Ishizuka , Naoto Nagaosa Using the formalism of time dependent nonequilibrium Green's functions (TDNEGF) we investigate the transport properties of RiceMele model when irradiated with ultrashort light pulse in the absence of any bias voltage. The model consists of a chain in which there are two kinds of atoms leading to different onsite energies along with hopping potential that changes from one atom to other. We then attach leads made out of a simple 1D chain and illuminate the RiceMele chain with an ultrashort (i.e. femtosecond duration) light pulse whose central frequency is equal to the energy gap of RiceMele model. While the timedependent current oscillates following the pulse, there is an average current and a total charge is injected into the leads. Such a shift current exists even when RiceMele chain is short enough that evanescent wave functions from the leads fill its gap and make the whole device metallic because the whole process can be viewed as nonadiabatic charge pumping where the key requirement is broken leftright spatial symmetry. Finally, we quantify the velocity of propagation of shift current generated in the center of clear or disordered RiceMele chain and compare with recent experiments [Ref : M. Nakamura et al., Nature Commun. 8, 281(2017)]. 
Thursday, March 8, 2018 11:51AM  12:03PM 
S08.00004: Lattice dynamics and anharmonicity: comparing first principles calculations and measurements Lucas Lindsay , Saikat Mukhopadhyay , Liangbo Liang , Carlos Polanco , Joshua Caldwell , Alexander Giles , Michael McGuire , Alexander Puretzky , Brian Sales The interplay of experiment and theory is critical to building basic insights and fundamental principles into physical phenomena, and yet comparison of measurement and calculations is not always straightforward in practice. Here we discuss the relationship of measurement probes (Raman, neutrons and xrays) and first principles calculations of lattice vibrations and anharmonicity as they apply to a variety of semiconducting materials. In particular, we will discuss our recent efforts in benchmarking phonon frequencies, density of states and lifetimes in MoS_{2}, CuCl, Tl_{3}VSe_{4}, MoCl_{3}, hBN and other materials. 
Thursday, March 8, 2018 12:03PM  12:15PM 
S08.00005: Diffusive realtime dynamics of a particle with Berry curvatures Kou Misaki , Seiji Miyashita , Naoto Nagaosa Motivated by the recent developments of timeresolved experiments, we study theoretically the influence of Berry phase on the realtime dynamics focusing on the diffusive dynamics, i.e., the timedependence of the distribution function. We found that the dynamics at the early stage is deeply influenced by the Berry curvatures in realspace (B), momentumspace (Ω), and also the crossed space between these two (C). For example, it is found that Ω induces the rotation of the wave packet and causes the timedependence of the mean square displacement of the particle to be linear in time t at the initial stage; it is qualitatively different from the t^{3} dependence in the absence of the Berry curvatures. It is also found that Ω and C modifies the characteristic time scale of the thermal equilibration of momentum distribution. Moreover, the dynamics under various combinations of B, Ω and C shows singular behaviors such as the critical slowing down or speeding up of the momentum equilibration and the reversals of the direction of rotations. These results offer yet another method to disentangle Berry curvatures in terms of timeresolved experiments. Possible experimental observations for excitons and trions in transition metal dichalcogenides are also discussed. 
Thursday, March 8, 2018 12:15PM  12:27PM 
S08.00006: Optical investigation on oxygen defect states in SrTiO_{3} compounds Yunsang Lee , Junwhi Lim , Sang A Lee , Woo Seok Choi We investigated oxygen defect states in SrTiO_{3} (STO) thin films by using the photoluminescence spectroscopy and spectroscopic ellipsometry. The oxygendeficient STO thin films were thermally treated in various oxygen environments systematically. The visible emission and absorption increased simultaneously with the increase of the oxygen vacancy concentration in the STO thin films. On the basis of the absolute values of the optical constants, we discussed the origins of the visible absorption features in STO, in relation to the defect formation and related electronic reconstruction. We also investigated the STO single crystals in the similar experimental procedure, and compared the results with the case of the thin films. 
Thursday, March 8, 2018 12:27PM  12:39PM 
S08.00007: CH_{3}NH_{3}PbX_{3} perovskites: Excellent microwave absorption Heng Guo , Jian Yang , Haiyuan Chen , Xiaobin Niu Given the remarkable progress in physical and structural performances of organicinorganic lead halide perovskites as a superstar in the photovoltaic field, the study of some intrinsic properties are still missing. Herein, we report the microwave absorption performance in CH_{3}NH_{3}PbX_{3} (X = I, Br and Cl) perovskite single crystals in terms of complex permittivity and permeability. We find that the CH_{3}NH_{3}PbI_{3}, CH_{3}NH_{3}PbBr_{3} and CH_{3}NH_{3}PbCl_{3} perovskites possess excellent microwave absorbability, and the optimum reflect losses reach 55.2, 54.7 and 46.4 dB at 16.8, 15.5 and 13.5 GHz with a matching thickness of 1.62, 1.76 and 1.95 mm, respectively. We explore the absorption mechanism. The microwave absorption properties are ascribed to the combination of dielectric and magnetic loss, but mainly for dielectric loss. In addition, the stability of microwave absorbability is also investigated, significantly dependent on the decomposition of corresponding perovskites. These results highlight the importance to the discovery of microwave absorbability in organicinorganic lead halide perovskites. More importantly, our study provides perovskite absorbers as a new variable to consider in the quest for future microwave devices. 
Thursday, March 8, 2018 12:39PM  12:51PM 
S08.00008: Field Modulation Imaging of Polarization Domain Dynamics in SingleCrystalline Organic Ferroelectric Thin Films at Various Temperatures Yohei Uemura , Shunto Arai , Jun’ya Tsutsumi , Satoshi Matsuoka , Sachio Horiuchi , Tatsuo Hasegawa Ferroelectrics have switchable spontaneous electric polarization, the feature of which is useful in nonvolatile memories or ferroelectric fieldeffect transistors. Among a variety of ferroelectric materials, protontransfertype organic ferroelectrics [1] are promising as key materials in flexible printed electronics due to the processability at ambient conditions. However, the studies of these materials are limited, because the ferroelectric domain dynamics as well as film fabrication methods have been unknown. 
Thursday, March 8, 2018 12:51PM  1:03PM 
S08.00009: Unusual Frequency of Quantum Oscillations in Strongly ParticleHole Asymmetric Insulators Hridis Pal Quantum oscillations, conventionally thought to be a metallic property, have recently been shown to arise in certain kinds of insulators, with properties very different from those in metals. All departures from the canonical behavior found so far appear in the amplitude and the phase but not in the frequency. Here I show that such robustness in the behavior of the frequency is only valid for a particlehole symmetric insulator; in a strongly particlehole asymmetric insulator, de Haasvan Alphen oscillations (oscillations in magnetization and susceptibility) and Shubnikovde Haas oscillations (oscillations in the density of states) exhibit different frequencies, with the frequency of the latter changing with temperature. I demonstrate these effects with numerical calculations on a lattice model, and provide a theory to account for the unusual behavior. The relevance of the theory in the context of recent experiments on SmB_{6} is discussed. 
Thursday, March 8, 2018 1:03PM  1:15PM 
S08.00010: Quantization of the heat polarization in twisted spacetime Ryota Nakai , Shinsei Ryu , Kentaro Nomura We study the heat polarization in the quantum Hall system in 2+1dimensional twisted spacetime. In analogy with the quantum Hall effect, the quantized thermal Hall effect can be explained by defining the heat polarization and the heat magnetization, the theory of which is based on the spacetime geometry. In this study, we consider a diffeomorphism of spacetime by twisting the boundary condition in both spatial and temporal directions. We will show that the diffeomorphism in the quantum Hall system induces heat transfer between boundaries, which gives rise to the heat polarization. 
Thursday, March 8, 2018 1:15PM  1:27PM 
S08.00011: Optical phonons in layer crystal of As_{2}S_{3}: effect of weak interlayer interaction. Sergey Mamedov , Natalia Drichko As_{2}S_{3} is known as layer crystal with structure which is very similar to the metal chalcogenides as MoS_{2} and some other. In such crystalline structure, the molecular unit is indefinitely extended in two dimensions. Centerzone optical phonons in 2D layer crystal As_{2}S_{3} have been investigated in Raman scattering in temperature range of 4K300K for both polarizations in the layer plane. Analysis of the symmetry of the crystal and 2D symmetry of the individual layer reveals that two symmetries predict different selection rules for optical phonons. Because crystal unit cell contains two layers, there are two times more (60) normal mode for the crystal compare to the layer (30). In the vanishing interaction between the layers, 60 modes collapse to 30 degenerated doublets. Weak interlayer interaction lifts these degeneracies with results of closely spaced doublets. Our experimental data show strong polarization dependence of Raman bands in ac plane at 134.4, 152.3, 185.5, 290.0, 309.4 and triplet 351.8, 354.1, 356.9 cm^{1}. The important evidence for the dominance of layer symmetry, along with very weak interaction between the layers, provides understanding of structural motives of As_{2}S_{3} and may predict optical/electronic properties of similar 2D materials. 
Thursday, March 8, 2018 1:27PM  1:39PM 
S08.00012: Ab initio Thermochemistry of the Si_{2}N_{2}(NH) analog of Si_{2}N_{2}O Andrew Chizmeshya , Narges Masoumi , George Wolf

Thursday, March 8, 2018 1:39PM  1:51PM 
S08.00013: Two Kinds of Local Temperature in Boltzmann Theory of Inhomogeneous Vibrational Heat Transport Philip Allen , Vasili Perebeinos Heat in insulators, carried by phonons, is described by the Peierls Boltzmann equation (PBE). In nanoscale situations, the heat current is partly diffusive (from phonons with mean free paths (mfp) less than sample size L), and partly ballistic (mfp > L). We find that, when the temperature gradient varies spatially, the local temperature T(r) appearing in the PBE differs from the temperature associated with the total nonequilibrium energy. This latter temperature is probably measured by most external probes. Our relaxation time approximation (RTA) solutions of the PBE quantify the difference, which is typically 5—20%. The difference depends on how much dispersion there is in phonon scattering rates 1/τ_{Q}, and disappears if 1/τ_{Q}=constant. The temperature difference does not seem to be an artifact of the RTA. 
Thursday, March 8, 2018 1:51PM  2:03PM 
S08.00014: Spinmomentum locked interaction between guided photons and surface electrons in topological insulator Bi_{2}Se_{3} Li He , Siyuan Luo , Mo Li The propagation of electrons and photons can respectively have the spinmomentum locking effect (SML) which correlates the spin with the linear momentum. A direct connection between the electron and photon spin occurs in topological insulators (TIs) with lifted spin degeneracy, which results in circular photogalvanic effect. Here, we study the photogalvanic effects in exfoliated Bi_{2}Se_{3 }by measuring the dependence of photoresponse on crystal orientation. In contrast to the linear photogalvanic effect that shows 3fold rotation symmetry on crystal orientation, an isotropic photoresponse is observed for the circular photogalvanic effect, indicates the corresponding optical transitions indeed involve surface bands. Furthermore, we demonstrate an optoelectronic device that integrates a TI with a photonic waveguide. Interaction between the photons in the waveguide, which carries optical spin, and the surface electrons in a Bi_{2}Se_{3} generates a directional photocurrent. Because of SML, the device works in a nonreciprocal way such that changing the light propagation direction reverses the optical spin and thus the direction of the photocurrent in TI. 
Thursday, March 8, 2018 2:03PM  2:15PM 
S08.00015: Ultralow thermal conductivity of single crystalline BaTiS3 Bo Sun , Nina Shulumba , Shanyuan Niu , Jayakanth Ravichandran , Austin Minnich BaTiS3 (BTS) is a new perovskitelike material that has promising optical, electronic and thermal properties, with potential applications in electronics and thermoelectrics. We report measurements of thermal conductivity of BTS single crystal from 80 K – 300 K using timedomain thermoreflectance. The room temperature thermal conductivity of BTS is found to be 0.5 W m1 K1, which is less than 10% of that of commonly known BaTiO3. To understand the origin of such low thermal conductivity we perform ab initio calculations using the temperature dependent effective potential (TDEP) method [1, 2] to study phonon transport at finite temperature. The strong temperature dependence of phonon modes and low group velocities lead to ultralow values of lattice thermal conductivity, supporting the experimental observation. 
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