Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session U44: Electrons, Phonons, Electron Phonon Scattering, and Phononics VIFocus
|
Hide Abstracts |
Sponsoring Units: DCOMP DMP Chair: Hans Braun, University of Bayreuth Room: 704 |
Thursday, March 5, 2020 2:30PM - 3:06PM |
U44.00001: Phonons in van der Waals materials and heterostructures: New probes & novel applications Invited Speaker: Aditya Sood Van der Waals (vdW) layered 2D materials and heterostructures are exciting candidates for applications in electronics and photonics. Heat dissipation presents a significant bottleneck that limits device performance. What determines the intrinsic limits of thermal transport in vdW materials? How do phonons transmit at interfaces between individual 2D layers? Can we create active thermal devices by manipulating phonon scattering rates in real time? I will present experiments designed to answer these questions, using new probes such as spatially-resolved ultrafast microscopy, femtosecond electron diffraction, and picosecond X-ray diffraction. First, I will discuss measurements of the out-of-plane thermal conductivity in thin layered crystals. Contrary to what is generally expected, we uncover evidence of propagating phonons with long mean-free-paths spanning 100s of layers. Next, to break the coherence of these vibrational modes, we use electrochemical ion insertion and achieve large reversible modulation (~10x) of thermal conductance in a nm scale device. Such thermal transistors could have interesting applications for the dynamic routing of heat. Finally, I will discuss experiments designed to elucidate interfacial energy transport at 2D heterojunctions. By addressing basic questions about the role of vibrational mismatch, we create synthetic solids with ultralow thermal conductivity. Using a new femtosecond electron diffraction technique, we probe strong coupling between photoexcited electrons and lattice vibrations in a type-II heterostructure, and directly visualize energy transport across a single vdW junction. |
Thursday, March 5, 2020 3:06PM - 3:18PM |
U44.00002: Ab Initio Electron-Defect Interactions Using Wannier Functions I-Te Lu, Jinsoo Park, Jin-Jian Zhou, Marco Bernardi The interactions between electrons and crystallographic defects control electron scattering and transport at low temperature. Electron-defect (e-d) interactions and the associated matrix elements can be computed from first principles using density functional theory through a method we recently developed. However, relevant quantities such as the e-d relaxation times (RTs) and carrier mobility require integrals over very fine Brillouin zone grids. Since computing a large number of e-d matrix elements is expensive, convergence and accuracy at a reasonable computational cost are challenging to achieve. In this talk, we present a Wannier interpolation scheme for e-d matrix elements and apply it to example calculations of vacancy defects in semiconductors and metals. We discuss the accuracy and versatility of the interpolation scheme, which can correctly reproduce the matrix elements computed directly, and apply it to compute and systematically converge e-d RTs and defect-limited charge transport properties at low temperature. We outline how our Wannier interpolation scheme for e-d interactions can serve as a powerful ab initio tool for studying a wide range of low-temperature transport phenomena and e-d interactions in materials. |
Thursday, March 5, 2020 3:18PM - 3:30PM |
U44.00003: Capturing non-perturbative electron-phonon effects in real materials using DMFT Adam Denchfield, Hyowon Park, Peter B Littlewood Dynamical Mean Field Theory (DMFT) can capture dynamical correlation effects on real materials by combining with Density Functional Theory (DFT) and solving the DMFT equation self-consistently within the multi-orbital Hubbard model extracted from DFT. Using a similar philosophy, we show that a multi-orbital Hubbard-Holstein model can be constructed from DFT electron-phonon calculations. We then derive an effective Hubbard model with a frequency-dependent electron-electron interaction U(ω) by integrating out the phonon degrees of freedom. This model can be solved using DMFT to capture the non-perturbative electron-phonon and electron-electron interaction effects. As a proof of the concept, we calculate phase diagrams of the two-orbital Hubbard-Holstein model as functions of the Coulomb interaction, the electron-phonon coupling, and temperature. We use Niobium to illustrate the process on a real material by obtaining model parameters from DFT, obtaining new insights on the effect of electron-phonon interactions in Niobium. |
Thursday, March 5, 2020 3:30PM - 3:42PM |
U44.00004: Computation of Phonon-Mediated Resistivity in Sr2RuO4 Felix Antoine Goudreault, Michel Cote, Feliciano Giustino, Samuel Ponce Because of its strong structural similarities to some high-Tc cuprates, Sr2RuO4 (SRO), a supposedly correlated superconductor, is attracting a lot of attention recently. Even though the discovery of superconductivity in SRO happened more than 20 years ago, the nature of the superconducting gap symmetry is still debated today. SRO also bears other unconventional properties like the strong anisotropy of the temperature dependence of its resistivity. Indeed, at low temperature, resistivity behaves like a highly anisotropic 3D Fermi-liquid, but low metallic transport has been reported for the in-plane resistivity at high temperature while the out-of-plane resistivity possesses a transition from metallic to incoherent transport mechanism around 130K which remains unexplained. In order to shed light on these phenomena, we carried out ab initio calculations to compute the electron-phonon coupling in SRO in the framework of density functional theory as implemented in the Quantum ESPRESSO software. Then, using the EPW code of the Quantum ESPRESSO suite, we report the temperature dependent phonon-mediated resistivity of SRO as computed from the Iterative Boltzmann Transport Equation scheme. |
Thursday, March 5, 2020 3:42PM - 3:54PM |
U44.00005: Ab initio study of spin and momentum relaxation in Elliott-Yafet spin decoherence Jinsoo Park, Jin-Jian Zhou, Marco Bernardi In the Elliott-Yafet (EY) theory, spin decoherence near room temperature is mainly mediated by electron-phonon (e-ph) interactions. The conventional wisdom is that the EY spin and momentum relaxation times are directly proportional. This proportionality has been widely used to analyze spin relaxation mechanisms in many different materials, although it is justified only for simple model systems. Here, we use our recently developed first-principles method [1] to compute independently and analyze the e-ph spin-flip and momentum-scattering interactions. We reveal stark differences between the two, and show that the EY spin and momentum relaxation mechanisms are governed by distinct microscopic processes, both in simple materials such as silicon and diamond and in complex topological semimetals. We demonstrate that the widely used proportionality between EY spin and momentum relaxation times is inaccurate, and so is the Elliott approximation relating the two. Our results highlight the need for atomistic spin relaxation calculations that take into account the electronic wave function, spin texture, phonon modes and their mode-dependent spin-phonon interactions. |
Thursday, March 5, 2020 3:54PM - 4:06PM |
U44.00006: Ab Initio Approach for Exciton Dynamics Hsiao-Yi Chen, Marco Bernardi We investigate exciton dynamics from first principles by combining our recently developed formalism to compute exciton-phonon (ex-ph) interactions with the Boltzmann transport equation (BTE) to simulate the exciton non-equilibrium dynamics. The computations are challenging – the ex-ph interactions require solving the finite-momentum Bethe Salpeter equation and density functional perturbation theory on fine Brillouin zone grids, and time-stepping the exciton BTE requires a parallel algorithm to explicitly time-step the exciton occupations. We apply our approach to transition metal dichalcogenides, focusing on the time scale for exciton valley decoherence and on exciton transport and relaxation. Our work provides a rigorous framework for computing exciton dynamics in materials from first principles, advancing the understanding of ultrafast excited state dynamics in materials. |
Thursday, March 5, 2020 4:06PM - 4:18PM |
U44.00007: Phonon-limited carrier mobility in semiconductors: importance of the dynamical quadrupoles Guillaume Brunin, Henrique Miranda, Matteo Giantomassi, Miquel Royo, Massimiliano Stengel, Xavier Gonze, Gian-Marco Rignanese, Geoffroy Hautier First-principles computations of phonon-limited carrier mobilities in semiconductors have recently gained popularity. Such calculations are indeed crucial for the discovery and development of new functional materials. |
Thursday, March 5, 2020 4:18PM - 4:30PM |
U44.00008: First-principles charge transport including electron-two-phonon scattering processes Nien-En Lee, Jin-Jian Zhou, Hsiao-Yi Chen, Marco Bernardi Predicting charge transport in materials from first principles is an open challenge. Although much progress has been made recently, nearly all work to date has relied on electron-phonon (e-ph) interactions obtained from lowest-order perturbation theory. However, in materials with polar bonds, the e-ph interactions are long-ranged, so assuming that higher-order e-ph processes are negligible is not justified. We recently investigated electron-two-phonon (e-2ph) scattering processes, and showed that these higher-order contributions are substantial even in a weakly polar material like GaAs [N.-E. Lee et. al., arxiv 1903.08261]. |
Thursday, March 5, 2020 4:30PM - 4:42PM |
U44.00009: Ab Initio Study of Impurity and Defect Scattering of Electrons in Nb and Nb3Sn* Nathan Sitaraman, Tomas Alberto Arias This talk will present ab initio density functional theory results on the effect of defects and impurities in Nb and Nb3Sn on electron mean free path at cryogenic temperatures. The mean free path is a key quantity of interest for scientists studying the properties of superconducting radiofrequency (SRF) cavities used in particle accelerators. Using a Wannier-function based approach, we calculate electron velocities and scattering lifetimes for dense samples of states near the complex Fermi surfaces of these materials. We compare the resulting mean free path estimates to experimental measurements, and present insights into the relative importance of different impurities and defects. We discuss other potential applications of the Wannier-function method to the study of impurites and defects, such as the calculation of inelastic scattering amplitudes. |
Thursday, March 5, 2020 4:42PM - 4:54PM |
U44.00010: Anharmonicity and Ultra-Low Thermal Conductivity in Lead-Free Halide Double Perovskites Johan Klarbring, Olle Hellman, Igor Abrikosov, Sergei Simak The lead-free halide double perovskite class of materials offers a promising venue for resolving issues related to the presence of toxic Pb and long-term stability of the very intensively studied class of single lead halide single perovskites. |
Thursday, March 5, 2020 4:54PM - 5:06PM |
U44.00011: Interfacial thermal transport between large lattice mismatch materials enhanced by atomic defects Zexi Lu, Petr Sushko, Amra Peles, Anne Chaka Control of interfacial thermal transport across complex interfaces is predicated on our ability to identify and (de-)couple contributions associated with low-dimensional interfacial features and structural and compositional inhomogeneities. In this study, we aim to reveal the relationship between interfacial thermal transport and defects, and establish its connection with underlying phonon-interfacial defect scattering mechanisms. We combine classical non-equilibrium molecular dynamics (MD) simulations with normal mode analysis (NMA) to investigate thermal transport across Cu/Si interface as a function of defect concentration in the interfacial region. We find that vacancies have a dramatic effect: interfacial thermal conductance increases by as much as 76% for the surface vacancy concentration of only 3%. NMA decomposition of the spectral phonon heat flux suggests that interfacial defects strongly affect inelastic phonon transmission. Our results establish relationships among the distribution of near interface defects, the extent of intermixing, thermal conductance and phonon scattering. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700