Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W44: Electrons, Phonons, Electron Phonon Scattering, and Phononics VII 
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Sponsoring Units: DCOMP DMP Chair: Mu Wang, Nanjing University Room: 704 
Friday, March 6, 2020 8:00AM  8:12AM 
W44.00001: Nonperturbative Estimates of Electrical Current in 2D Dirac Systems  A MoS2 Example David N. Carvalho The term “Dirac materials” refers to a large set of seeminglydisparate materials which share many universal properties and may be described by the Dirac equation. The effect of external timedependent fields on their carrier dynamics is of great importance. However, due to the noncommutativity of the Dirac Hamiltonian in time domain, nonperturbative estimates of the propagator of a Dirac spinor are challenging to obtain. 
Friday, March 6, 2020 8:12AM  8:24AM 
W44.00002: Driven Imposters: Controlling Expectations in Solid State Systems Gerard McCaul, Christopher Orthodoxou, Kurt Jacobs, George Booth, Denys Bondar We present a model to control the observables of a general manybody electron system driven by an incident laser field. The main result is a nonlinear, field free equation of motion for tracking observables, together with a constraint on the functional form of expectations which may be reproduced via tracking. As a first test, the strategy is used in the FermiHubbard model to make the current expectation conform to an arbitrary function under a range of model parameters. Additionally, using two reference spectra for materials in the conducting and insulating regimes respectively, we demonstrate that using the developed tracking strategy allows one to make the dipole acceleration spectrum of each material mimic the reference spectra of the other, creating a 'driven imposter'. 
Friday, March 6, 2020 8:24AM  8:36AM 
W44.00003: Noise mediated mixing in a tunnel junction Samuel Houle, Edouard Pinsolle, Joffrey Rivard, Christian Lupien, Bertrand M Reulet The microwave mixer is a key element in the detection of all sort of 
Friday, March 6, 2020 8:36AM  8:48AM 
W44.00004: Modeling Spontaneous Charge Transfer at Metal / Organic Hybrid Heterostructures Ongun Ozcelik, Yingmin Li, Wei Xiong, Francesco Paesani Hybrid heterostructures are crucial in photovoltaics where the overall efficiency of the materials are closely related to the level of charge transfer at their interfaces. Here, using a combined computational and experimental approach, we show that heterodyne vibrational sum frequency generation (HDVSFG) measurements provide an effective way of monitoring the interfacial charge transfer in these heterostructures [1]. Using abinitio quantum chemical calculations, we show that inducing regiorandomness into the organic polymer modifies the interfacial electronic states, level of hybridization and the electronic wave function of these materials. We present the HDVSFG responses of the metal/P3HT heterojunctions containing both regioregular and regiorandom P3HT structures and show that the intensity of nonresonant signal is directly correlated with the computed electronic structure and the level of spontaneous charge transfer at these interfaces. 
Friday, March 6, 2020 8:48AM  9:00AM 
W44.00005: Enhancement of superconductivity in organicinorganic hybrid topological materials Haoxiong Zhang, Awabaikeli Rousuli, Shengchun Shen, Kenan Zhang, Chong Wang, Laipeng Luo, Jizhang Wang, Yang Wu, Yong Xu, Duan Wenhui, Hong Yao, Pu Yu, Shuyun Zhou Inducing or enhancing superconductivity in topological materials has attracted extensive research interests partly due to its fundamental importance toward topological superconductivity. Reducing the thickness of transition metal dichalcogenides has provided an important pathway to engineer superconductivity in topological matters, emergent superconductivity with T_{c} ~ 0.82 K in monolayer WTe_{2} which also hosts intriguing hightemperature quantum spin Hall effect. However, such monolayer samples are often difficult to obtain and extremely sensitive in air. Here we report a generic, experimentally convenient approach to manipulate the interlayer coupling in bulk MoTe_{2} and WTe_{2} single crystals through organic cation intercalation. The asformed organicinorganic hybrid crystals exhibit dramatically enhanced superconductivity with T_{c} of 7.0 K for intercalated MoTe_{2} (as compared with 0.25 K for bulk crystal) and 2.3 K for intercalated WTe_{2} (record high compared to monolayer WTe_{2} and with greatly improved sample stability). This organiccationintercalation method can be readily applied to many other layered crystals, forming a promising research platform to manipulate their corresponding electronic states, including possible topological superconductivity with significantly enhanced T_{c}. 
Friday, March 6, 2020 9:00AM  9:12AM 
W44.00006: Pressure Control of Crystal Symmetry, Fermi Surface Reconstruction and Superconductivity in Weyl semimetal MoTe_{2} Taner Yildirim, ILin Liu, Colin Heikes, Chris Eckberg, Tristin Metz, Sheng Ran, William Ratcliff, Johnpierre Paglione, Nicholas Butch Layered transition metal chalcogenides are promising hosts of electronic Weyl nodes and topological superconductivity. MoTe_{2} is a striking example that harbors both noncentrosymmetric T_{d} and centrosymmetric T' phases. In this talk we present neutron scattering and transport mreasuremens along with Density functional theory (DFT) calculations to suggest a path towards the realization and control of these topological states of the typeII Weyl semimetal and superconductor MoTe_{2} through the application of pressure [1]. DFT calculations reveal that the strength of the electronphonon coupling is similar for both crystal structures. Finally, we show that there is a critical pressure characterized by unique coherent quantum oscillations, indicating that the change in topology between two phases give rise to a new topological interface state[2]. We present periodic and finite slab calculations of this new interface state which is in excellent agreement with the observed quantum oscillation frequencies. 
Friday, March 6, 2020 9:12AM  9:24AM 
W44.00007: Discovering topological surface states of Dirac points in an acoustic crystal hengbin cheng, Yixin Sha, Rongjuan Liu, Chen Fang, Ling Lu Dirac materials, unlike the Weyl materials, have not been found in experiments to support intrinsic topological surface states, as the surface arcs in existing systems are unstable against symmetrypreserving perturbations. Utilizing the proposed glide and timereversal symmetries, we theoretically design and experimentally verify an acoustic crystal of two frequencyisolated threedimensional Dirac points with Z_{2} monopole charges and four gapless helicoid surface sheets. Under symmetry breakings, the 3D ideal Dirac point breaks into Z_{2} Weyl dipoles, Z_{2} nodal rings or a full bandgap. 
Friday, March 6, 2020 9:24AM  9:36AM 
W44.00008: Timeresolved xray diffraction study of acoustic phonons in TaAs MinCheol Lee, Nicholas Sirica, Samuel W. Teitelbaum, Mariano Trigo, Gilberto Antonio de la Pean Munoz, Viktor Krapivin, Yijing Huang, David A Reis, Alexei Maznev, Jiaojian Shi, Keith Adam Nelson, Roxanne Tutchton, JianXin Zhu, Xianggang Qiu, Dzmitry Yarotski, Rohit P Prasankumar We utilized femtosecond xray pulses to investigate acoustic phonon oscillations in TaAs. We observed that timeresolved xray diffraction reveals coherent phonon oscillations of binary acoustic modes in truncation rod scattering. The phonon oscillations correspond to the transverse and longitudinal acoustic modes propagating along the surface normal vector. We suggest that the offaxis orientation of the surface normal makes it possible to observe the transverse phonon oscillation, in contrast to conventional laserinduced acoustic phonon oscillations due to a single longitudinal mode. We also found an asymmetric Fanolike feature in the longitudinal phonon oscillations, suggestive of strong electronphonon coupling in TaAs. 
Friday, March 6, 2020 9:36AM  9:48AM 
W44.00009: Spectral signatures of excitonpolarons in twodimensional hybrid leadhalide perovskites Felix Thouin, Carlos Silva

Friday, March 6, 2020 9:48AM  10:00AM 
W44.00010: Density functional perturbation theory with subspace iteration Saeed Bohloul, Vincent Michaud, Hong Guo Density functional perturbation theory (DFPT) is a useful framework for calculating material responses that can be casted as total energy derivatives with respect to perturbation fields. These responses give access to important properties including the dynamical matrix, dielectric functions, optical properties, electronphonon coupling, etc. A major advantage of DFPT is circumventing the computational burden of direct methods by replacing DFT supercell calculations, one for each possible perturbation, by a system of coupled linear equations for primitive cells which are solved selfconsistently. Nevertheless, for unit cells containing a large number of atoms, solving this linear system becomes a major bottleneck. In this work, we report a new approach to overcome this bottleneck of DFPT, the perturbed Chebyshevfiltered subspace iteration (PCFSI) method, implemented in real space. It allows us to calculate responses of materials in much larger systems than was possible before. Dielectric functions and phonon spectra will be used as examples to demonstrate the impressive power of the PCFSI method. 
Friday, March 6, 2020 10:00AM  10:12AM 
W44.00011: Theories, designs, and applications of thermal metamaterials Liujun Xu, Shuai Yang, Jiping Huang With the growing concerns about energy issues, many researchers have paid their attention to thermal management. This trend was mainly driven by the emerging field of thermal metamaterials in the last decade.This report mainly introduces the new progress of thermal metamaterials in three aspects: new functions, multiparticle systems, and intelligentization. The new functions include the thermal "golden touch" and the thermal Janus structures. The former is a method to extend the core property to the shell with an extremely small core fraction. The latter is essentially a coreshell structure whose core has two distinct thermal conductivities, and the mechanical rotation of the core can realize different functions. Multiparticle systems extend the coreshell design, and the multiparticle interaction helps us achieve thermal invisibility. Intelligentization means that the effective thermal conductivity of a shell is always the same as that of the environment. 
Friday, March 6, 2020 10:12AM  10:24AM 
W44.00012: Optical Properties of Complex Oxides RbFe(MoO_{4})_{2}, RbFe(SO_{4})_{2}, and RbFe(SeO_{4})_{2} Rachel Owen, Elizabeth Drueke, Charlotte Albunio, Alemayehu S Admasu, Junjie Yang, SangWook Cheong, Steven Thomas Cundiff, Liuyan Zhao The structural and magnetic properties of the archetype typeII multiferroic RbFe(MoO_{4})_{2} have been well studied due to interest in the low temperature antiferromagnetic order and its coupling to the induced ferroelectric order. However, little is known about the optical properties of this complex oxide. There have been low energy spectroscopic characterizations, but no reported linear characterization up into the band edge. Here we explore a group of similar such complex oxides: RbFe(MoO_{4})_{2}, RbFe(SO_{4})_{2}, and RbFe(SeO_{4})_{2}. Substitution of the Asite in RbFe(AO_{4})_{2} can result in comparable, spectrally tunable absorption features that appear below the optical transition band edges. Their absorption spectra show strikingly similar thickness and temperature dependence, despite their different growth conditions and electronic/magnetic properties. We further discuss the potential origin and impact of these tunable optical transition states in the RbFe(AO_{4})_{2} complex oxide family. 
Friday, March 6, 2020 10:24AM  10:36AM 
W44.00013: Nonlinear optics with ionizing radiation and ultrafast lasers: progress toward measuring the complete electric field of XFEL pulses William Peters, Travis Jones, Richard L Sandberg, Pamela Bowlan Newly developed Xray free electron lasers (XFELs) promise to transform nearly all areas of modern science. However, there is a significant need for more sophisticated tools to measure the Xray pulses themselves. Complete measurements of the pulse’s electric field are needed to improve the light source technology and to enable new spectroscopy and scattering experiments. Here we describe measurement approaches in which an optical laser interacts with an interference pattern from the unknown XFEL pulse, referred to as a transient grating or as four wave mixing. This geometry largely isolates the instantaneous wavemixing response necessary for the FROG algorithm and removes the longlived response seen in other Xraypump opticalprobe measurements. The measurement also transfers the phase information of the Xray electric field onto a readilydetectable optical laser field, allowing us to fully characterize the unknown pulses with visible spectrometers and cameras. Crucially, our strategy promises to be broadly applicable across the entire energy range accessible by existing and planned XFEL facilities. Labscale UV demonstration experiments will be presented as well as results from an upcoming beam time at the FERMI soft Xray FEL. 
Friday, March 6, 2020 10:36AM  10:48AM 
W44.00014: Critical Behaviors of Anderson Transitions in Three Dimensional Orthogonal Classes with Particlehole Symmetries Xunlong Luo, Baolong Xu, Tomi Ohtsuki, Ryuichi Shindou From transfermatrix calculation of localization lengths and their finitesize scaling analyses, we evaluate critical exponent of the Anderson transition in three dimensional (3D) orthogonal class with particlehole symmetry, class CI, as ν = 1.16 [ .14, .18 ]. We further study disorderdriven quantum phase transitions in the 3D nodal line Dirac semimetal model, which belongs to class BDI, and estimate critical exponent as ν = 0.80 [ .78, .82 ]. From a comparison of the critical exponents, we conclude that a disorderdriven reentrant insulatormetal transition from the topological insulator phase in the class BDI to the diffusive metal phase belongs to the same universality class as the Anderson transition in the 3D class BDI. We also discover a topological quantum critical point (TQCP) between onedimensional (1D) class BDI topological insulator and Anderson insulator and showed that the reentrant transition in the 3D model is connected to the TQCP in its 1D limit. We argue that an infinitesimally small disorder drives the nodal line Dirac semimetal in the clean limit to the diffusive metal. 
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