Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q48: Electrons, Phonons, Electron-Phonon Scattering, and Phononics IVFocus Recordings Available
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Sponsoring Units: DCOMP DMP Chair: Davide Donadio, University of California Davis Room: McCormick Place W-471A |
Wednesday, March 16, 2022 3:00PM - 3:12PM |
Q48.00001: Chiral phonons in time reversal broken systems from first principles John R Bonini, Cyrus E Dreyer, Sinisa Coh The conventional approach to the calculation of phonon modes is via eigenvalues and eigenvectors of the dynamical matrix. However, the dynamical matrix is, by construction, time reversal symmetric even for systems with known time reversal breaking in the electronic sector. Such systems have been observed to display a number of effects involving time reversal broken ion dynamics including chiral phonons, the Einstein de Haas effect, and the phonon Hall effect. In this work we develop and apply a first-principles methodology for computing the leading order corrections beyond the usual dynamical matrix which captures such time reversal broken ion dynamics. This correction comes in the form of forces proportional to ion velocities which act on ions in addition to the forces proportional to ion displacements captured by the dynamical matrix. This linear order coupling between ion velocities and forces can be expressed as a matrix of ionic Berry curvatures. An application of the formalism to CrI3 using density functional theory is presented. The addition of the velocity force results in a 6% splitting of phonons modes which would have been found to be degenerate if computed from the dynamical matrix alone. |
Wednesday, March 16, 2022 3:12PM - 3:24PM |
Q48.00002: Precisely and efficiently computing phonons via irreducible derivatives: characterizing soft modes Sasaank Bandi, Chris Marianetti Computing phonons from first-principles is typically considered a solved |
Wednesday, March 16, 2022 3:24PM - 3:36PM |
Q48.00003: Assessing Temperature Dependence of Band Gap Renormalization in LaCrO3−δ via First-Principles and Experimental Corroboration Jongwoo Park, Jeffrey K Wuenschell, Benjamin Chorpening, Wissam A Saidi, Yuhua Duan For applications in combustion environments, understanding the temperature dependence of functional properties in high-temperature gas sensing materials is vital. The electron-phonon coupling that derives the electronic structure change with temperatures is a key property of interest as this affects other sensing responses. Herein, we assess the temperature dependence of band gap renormalization in pristine and oxygen-vacant LaCrO3-δ perovskite employing Allen-Heine-Cardona theory with first-principles simulations, and corroborate with experimental observation. We find fair agreement in temperature-dependent band gap change in LaCrO3 between theory and an in-house experiment, proving that the theory can adequately predict renormalization on the band gap in the system of interest. Band gaps in high-temperature phase of cubic LaCrO3-δ are found to be monotonically closed by 1.13 eV in pristine and by around 0.62 eV in oxygen-vacant states as a function of temperature up to 1500 K. The predicted and measured band gap variations are characterized using an analytical model, which can provide useful insights on the simulated zero-temperature band gaps. |
Wednesday, March 16, 2022 3:36PM - 3:48PM |
Q48.00004: Sub-Planckian electron diffusion in a model of ultrastrong electron-phonon coupling Calvin Pozderac, Brian Skinner The conjecture of the Planckian bound on transport implies a temperature-dependent lower bound on the electron diffusion constant. Motivated by this conjecture, we study a model of electron diffusion in the limit of ultrastrong electron-phonon coupling. In this limit, the phonons can be described by a semiclassical potential energy landscape that fluctuates slowly in time, while electrons are instantaneously equilibrated to lie in local minima of the potential. We study this model for both gapped (optical) and gapless (acoustic) phonon modes. We find diffusive behavior with a diffusion constant that scales as the inverse temperature, as in the naive Planckian bound, but with a small prefactor that can in principle give deeply sub-Planckian diffusion. |
Wednesday, March 16, 2022 3:48PM - 4:00PM |
Q48.00005: Impact of the transport formalism on the phonon-limited carrier mobilities in semiconductors Romain Claes, Guillaume Brunin, Matteo Giantomassi, Gian-Marco Rignanese, Geoffroy Hautier Carrier mobility is an essential property in many different applications. Solar cells, thermoelectrics, transparent conductors or even light-emitting devices are all areas that would benefit from a better understanding of transport quantities. Therefore, for the design of new devices, it is essential to have an efficient and low-cost method for calculating fully ab initio carrier (electron or hole) mobilities. Despite significant progress in the field since the late 2000s, very few bulk semiconductors have been investigated so far due to the complexity of the current methods. Recently, various works have reported the ab initio calculation of phonon-limited mobility for semiconductors using different methodologies [1-3]. In this work, we present the latest developments in ABINIT regarding the calculation of the phonon-limited mobility within the semi-classical Boltzmann transport formalism and results for new and state-of-the art materials. The importance of the scattering time on the transport properties as well as the approximations used will also be discussed. |
Wednesday, March 16, 2022 4:00PM - 4:12PM |
Q48.00006: Electronic transport properties from first-principles beyond the Boltzmann equation Andrea Cepellotti, Jennifer Coulter, Anders Johansson, Natalya S Fedorova, Boris Kozinsky In this talk we will present some of our efforts for characterizing materials transport properties from first-principles. We first discuss how semiclassical first-principles models are unable to capture the electronic transport properties of Bi2Se3, a narrow-gap semiconductor. We show that transport in this material at low doping concentrations is dominated by Zener tunneling, a phenomenon in which carriers tunnel between the valence and the conduction band, rather than diffuse under the action of the electric field. This transport mechanism is here described using a novel first-principles model based on the Wigner distribution. Surprisingly, we find that Zener tunneling is not limited to low-energy carriers, but occurs also between band subvalleys of energy larger than the band gap. Next, we introduce Phoebe, a new open-source software for computing thermoelectric properties by solving the electron and phonon Boltzmann equations. Phoebe computes electron-phonon and phonon-phonon scattering properties from first-principles simulations, allowing a fully ab-initio prediction of thermoelectric properties. Additionally, we implemented an efficient mixed MPI and OpenMP parallelization and GPU acceleration, allowing us to take advantage of modern computing infrastructure. |
Wednesday, March 16, 2022 4:12PM - 4:48PM |
Q48.00007: Towards a fully electromagnetic control of the heat flux Invited Speaker: Riccardo Rurali The development of phononics, the discipline that investigates phonon transport and aims at engineering devices with the same functionalities as electronic or photonic ones, has been hindered by the inherently challenging nature of phonon manipulation. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q48.00008: Harnessing modulated electrons to probe light-matter strong coupling Jaime Abad-Arredondo, Francisco José García Vidal, Antonio I Fernández-Dominguez Due to recent advances in the control of the quantum properties of collimated free-electron beams, these appear to be one of the most promising probes for quantum matter at the nanoscale. In this work, we provide a model Hamiltonian describing the quantum interaction between a modulated electron wave-packet and a hybrid photonic-excitonic system comprising a quantum emitter and an optical nanocavity. This Hamiltonian is constructed using macroscopic QED ideas and fully parameterized in terms of the electromagnetic Dyadic Green's function. We explore the Jaynes-Cummings polariton ladder of the cavity-emitter system through both the free-electron and photon spectra and demonstrate the power of modulated electrons as near-field probes of light-matter interactions in the strong-coupling regime. |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q48.00009: Automated computation of phonon-limited carrier mobilities in semiconductors Guillaume Brunin, Romain Claes, Matteo Giantomassi, 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. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q48.00010: Magnetotransport in semiconductors and two-dimensional materials from first-principles Dhruv C Desai, Bahdan Zviazhynski, Jin-Jian Zhou, Marco Bernardi Magnetic fields influence electrical transport in materials, with changes quantified by magnetotransport coefficients such as the magnetoresistance (MR), Hall mobility and Hall factor. In this talk, we present a first-principles method to study magnetotransport phenomena in materials by solving the Boltzmann transport equation (BTE) with ab-initio electron-phonon collisions in the presence of an external magnetic field [1]. We apply this approach to various semiconductors and two-dimensional (2D) materials, computing in each case the MR, Hall mobility and Hall factors. Our results are in very good agreement with experiments and shed light on the microscopic mechanisms governing magnetotransport. |
Wednesday, March 16, 2022 5:24PM - 5:36PM |
Q48.00011: Breakdown of LO-TO polar splitting in 1D materials and its application to nanowires and nanotubes Norma Rivano, Nicola Marzari, Thibault Sohier Accurate models and simulations of the vibrational properties of 1D materials are crucial for the analysis and prediction of transport and spectroscopic properties. In the long-wavelength limit, longitudinal polar-optical phonons (those probed by IR and Raman spectroscopies) are known to undergo a frequency shift which depends strongly on dimensionality. In 3D, this leads to a roughly constant separation between the optical modes across the Brillouin zone, termed LO-TO splitting. At variance with this, in 2D the dielectric shift has been shown to depend upon the phonon wavevector and to linearly vanish at small momenta1. Using analytical models and density-functional perturbation theory in a newly-implemented one-dimensional framework, we show that it also vanishes in 1D, but with a logarithmic asymptotic behavior. We demonstrate the relevance of our work by studying a portfolio of realistic systems: BN atomic-chain, BN armchair nanotubes and GaAs nanowires of varying size. We then discuss the polar and mechanical nature of the phonon energy shift and its dependency on dimensionality. This work not only provides useful insight into the vibrational physics of a wide class of 1D materials, but also a ready-to-use tool for the experimental community to encourage further studies. |
Wednesday, March 16, 2022 5:36PM - 5:48PM |
Q48.00012: Machine Learning aided Phonon Anarmonicity: the Soft Mode in the Quantum Paraelectric KTaO3 Luigi Ranalli, Carla Verdi, Lorenzo Monacelli, Georg Kresse, Matteo Calandra, Cesare Franchini Quantum paraelectric materials are characterized by atypical fluctuations of the polarization due to the anharmonic lattice dynamics at low temperatures [1]. In the incipient ferroelectric KTaO3 perovskite, the low-temperature transition towards a fully ferroelectric phase is driven by the coupling of translation and soft modes. This transition is not accurately described within the conventional harmonic approximation. Here, we adopt the Stochastic Self-Consistent Harmonic Approximation (SSCHA) [3] accelerated by Machine Learning Force Field (MLFF) [4] to determine the full anharmonic energy contribution and the renormalized phonon frequencies in KTaO3. The inclusion of the anharmonic terms leads to a fairly good agreement with the experimental phonon spectrum and shed light on the temperature evolution of the soft mode frequency and the quantum ferroelectic transition. The efficiency and precision of our MLFF-aided stochastic method may open new paths for the study of quantum paraelectrics and phonon instabilities in large systems. |
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