Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R44: Electrons, Phonons, Electron Phonon Scattering, and Phononics IVFocus
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Sponsoring Units: DCOMP DMP Chair: Ludger Wirtz, University of Luxembourg Limpertsberg Room: 704 |
Thursday, March 5, 2020 8:00AM - 8:36AM |
R44.00001: Phonon anharmonicity and structural transitions – neutron scattering and first-principles simulations Invited Speaker: Olivier Delaire Using a combination of inelastic neutron/x-ray scattering and first-principles simulations, we investigate anharmonic effects on phonons across phase transitions. This presentation will focus on transitions potentially associated with soft mode condensation. In particular, we will highlight results on phonons in SnS and SnSe across the high-temperature Pnma-Cmcm transition, in VO2 across the rutile-M1 transition, and NbNiTe2 across its subtle structural orthorhombic-monoclinic transition at 373K. The effects of phonon anharmonicity on thermal transport and thermodynamics will be discussed. |
Thursday, March 5, 2020 8:36AM - 8:48AM |
R44.00002: Ab initio study of electron and hole transport in a naphthalene crystal including polaron effects Benjamin Chang, Jin-Jian Zhou, Nien-En Lee, Marco Bernardi Organic semiconductors have broad applications in electronics, but their transport properties are notoriously difficult to predict due to their complex structure, strong electron-phonon (e-ph) interactions and localized charge carriers (polarons). We recently showed [1] calculations of the hole mobility in naphthalene, assuming band-like transport and using lowest-order ab initio e-ph interactions within the Boltzmann equation approach. Although our calculations provided hole mobilities in agreement with experiment, several open questions remain, such as improving the accuracy of the method and extending it to charge transport in the polaron regime. In this work, we employ our recently developed finite-temperature cumulant-expansion method [2] to compute the electron spectral functions, and from them the mobility, in a naphthalene crystal. Our method can correctly include strong e-ph interactions and polaron effects. We will discuss the carrier spectral functions and mobilities as a function of temperature in naphthalene, comparing the results with experiments and lowest-order theory. The applicability of our method to a range of organic crystals will be discussed. |
Thursday, March 5, 2020 8:48AM - 9:00AM |
R44.00003: Towards ultrafast control of dielectric response through nonlinear lattice excitation Guru Khalsa, Nicole A Benedek, Jeffrey A. Moses The development of intense laser sources in the infrared has created an opportunity for unprecedented ultrafast selective control of crystal structure. Striking changes in material properties have been achieved by the optical nonlinear phononics effect - where large amplitude infrared (IR) phonons drive Raman active phonons through nonlinear lattice coupling. [Rep. Prog. Phys. 79, 064503 (2016)] Excitation of IR phonons with light is conventionally described by coupling of the infrared electric field to a linear dipole induced by the IR phonon. When IR phonons are excited to large amplitude, when multiple optical phonons are displaced simultaneously, or when multiple laser sources are used concurrently, the conventional linear description of the crystal’s dipole may be insufficient. |
Thursday, March 5, 2020 9:00AM - 9:12AM |
R44.00004: Theoretical Study of Pressure-Induced Superconductivity in Palladium Chalcogenides Olivier Gingras, Felix Antoine Goudreault, Michel Cote The pressure-induced superconductivity observed in palladium chalcogenides is not fully understood. Although insulating at ambient conditions, increasing isotropic pressure in PdSe2 and PdS2 leads to metallic phases, followed by structural transitions. These materials eventually become superconductors at higher pressure. In PdSe2, the critical temperature is directly correlated with the bonding strength of Se-Se dumbbells, suggesting phonon mediated superconductivity[1]. However, the opposite is observed in PdS2[2]. In order to understand the pairing mechanism in these emerging superconducting materials, we investigate the different transition temperatures using first-principles density functional theory and test the phonon mediated pairing hypothesis by calculating the superconducting dome. |
Thursday, March 5, 2020 9:12AM - 9:24AM |
R44.00005: Renormalization of magnetic interactions due to thermal disorder from first principles Matthew Heine, Olle Hellman, David Broido In magnetic materials, temperature dependent magnetic properties can be investigated using a Heisenberg Hamiltonian. In such a picture, raising T increases disorder in local magnetic moment orientations, the interaction of which are governed by a constant exchange parameter, J. In a more complete picture, however, such increase in moment disorder may affect the strength of the moment interactions, thereby renormalizing J as a function of T, J(T). Moreover, raising T also increases lattice disorder, which may also renormalize the interaction J(T) via spin-lattice coupling thus affecting physical quantities such as M(T) and phonon frequencies. In this study, we extend the Temperature Dependent Effective Potential (TDEP) framework to calculate such renormalized J(T) from first principles. Density Functional Theory (DFT) is employed using constrained noncollinear magnetic moments. We calculate J(T), M(T) and phonons for the test case of bcc Fe and find good agreement with experiment. We also find the lattice disorder to significantly renormalize J in the vicinity of the Curie Temperature. |
Thursday, March 5, 2020 9:24AM - 9:36AM |
R44.00006: Emergence of Superconductivity Around Polar Quantum Critical Point in Doped Ferroelectrics JIAJI MA, Ruihan Yang, Hanghui Chen We combine first-principles calculations and Eliashberg equation to demonstrate that with itinerant electrons inducing a polar-to-centrosymmetric quantum critical point (pQCP) in doped ferroelectrics, softened zone-center polar phonon modes strongly couple to itinerant electrons, which enhances electron-phonon coupling around pQCP. By considering a prototypical ferroelectric material BaTiO3, we find that around its pQCP, electron-phonon coupling is increased to about 0.5, sufficiently large to induce phonon-mediated superconductivity with an optimal transition temperature of about 1 K. However, different from superconducting dome associated with other structural quantum critical points, around pQCP the superconducting transition temperature of doped BaTiO3 is enhanced much more substantially in the polar phase than in the cubic phase. |
Thursday, March 5, 2020 9:36AM - 9:48AM |
R44.00007: Electron-phonon interactions and photoemission kink in cuprates: A GW perturbation theory study Zhenglu Li, Meng Wu, Yang-hao Chan, Steven Louie The nexus of electron-phonon (e-ph) and many-electron interactions plays an important role in shaping the electron spectral function. We present first-principles calculations of the observed photoemission kink in cuprates using our recently developed method for e-ph coupling, the GW perturbation theory (GWPT) [1]. In this approach, the e-ph coupling is calculated using linear-response theory within the ab initio GW method, combined with Wannier interpolation technique. We find that self-energy effects significantly renormalize the e-ph interactions in the cuprates, giving rise to dramatic changes in the strength of the photoemission kink as compared with results from standard density-functional perturbation theory. |
Thursday, March 5, 2020 9:48AM - 10:00AM |
R44.00008: First-principles study of vibrational properties of lithium niobate Mona Asadi Namin, Steven Lewis We present first-principles calculations of the well-known non-linear optical material LiNbO3. Starting from the ground state properties, e.g. band structure of the stochiometric system, we use density functional perturbation theory to find the vibrational modes. Since LiNbO3 is a polar ferroelectric material that involves long range interactions, we use the Ewald summation to add the coulombic interaction to the dynamical matrix formalism. The transverse and longitudinal modes are in good agreement with the other ab-initio calculations, as well as the spectroscopic measurements. |
Thursday, March 5, 2020 10:00AM - 10:12AM |
R44.00009: BaTiO3 as electric field controllable reservoir of phonon angular momentum Kevin Moseni, Sinisa Coh We studied the angular momentum of phonons (PAM) in BaTiO3 from first principles. We find that the PAM is four times larger in directions perpendicular to polarization than parallel. Furthermore, PAM is strongly non-linear as a function of BaTiO3 tetragonality. We assign these observations to specific interatomic force constants in the material. Finally, we suggest experiments using BaTiO3 as an electric field controllable phonon angular momentum reservoir. |
Thursday, March 5, 2020 10:12AM - 10:24AM |
R44.00010: Lattice Dynamics and Electron Transport in α-Ga2O3 Ankit Sharma, Mahitosh Biswas, Elaheh Ahmadi, Uttam Singisetti Ga2O3 is an important wide bandgap material with applications ranging from power to RF electronics. It occurs in 5 polymorphs α, β, γ, δ and ε. β-Ga2O3 is extensively studied as it is thermodynamically a more stable phase & availability of bulk crystals. However, α-Ga2O3 has higher bandgap than β-phase, so better performance is expected for power applications. Although few reports exist on α-Ga2O3, it has not gained much traction as it is thermodynamically semi-stable making its synthesis challenging until recently where single crystalline α-Ga2O3 thin films were successfully grown. This opens a wide array of fields in device synthesis using α-phase (R3-c) which has a structure like corundum and thus can be potentially alloyed with materials like Cr2O3 and Fe2O3, with possibilities for magnetoelectric applications. We will present a detailed study of the lattice dynamics, electronic structure and low field electron transport properties in α-Ga2O3. Calculated Raman spectra is compared with experiments. The electron-phonon matrixelements are calculated under the DFT, DFPT and Wannier function formalism. We will also analyze the effects of temperature and doping on the mobility using the Boltzmann transport eqn. Emphasis will be laid on identifying the dominant scattering mechanism. |
Thursday, March 5, 2020 10:24AM - 10:36AM |
R44.00011: Superconductivity of Liquids Huiying Liu, Ying Yuan, Donghao Liu, Xin-Zheng Li, Junren Shi
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R44.00012: Coupling many-body-perturbation-theory calculations of electron-electron and electron-phonon coupling Han Yang, Marco Govoni, Giulia Galli Recently a method [1] was proposed to couple the calculations of G0W0 quasiparticle energies and electron-phonon scattering in molecules and nanostructures by using the spectral decomposition of dielectric matrices [2]. Here we generalize this approach to solids. Our implementation in the WEST [3] code (www.west-code.org) does not require summation over conduction bands or any self-consistent density-functional-perturbation-theory calculations. We validate our framework by computing phonon frequencies and electron-phonon lifetimes of several semiconductors and insulators, and we discuss the accuracy and efficiency of the method relative to existing techniques. |
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