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, ElectronPhonon Scattering, and Phononics IVFocus Recordings Available

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Sponsoring Units: DCOMP DMP Chair: Davide Donadio, University of California Davis Room: McCormick Place W471A 
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 firstprinciples 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 firstprinciples is typically considered a solved 
Wednesday, March 16, 2022 3:24PM  3:36PM 
Q48.00003: Assessing Temperature Dependence of Band Gap Renormalization in LaCrO_{3−δ} via FirstPrinciples 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 hightemperature gas sensing materials is vital. The electronphonon 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 oxygenvacant LaCrO_{3δ} perovskite employing AllenHeineCardona theory with firstprinciples simulations, and corroborate with experimental observation. We find fair agreement in temperaturedependent band gap change in LaCrO_{3} between theory and an inhouse experiment, proving that the theory can adequately predict renormalization on the band gap in the system of interest. Band gaps in hightemperature phase of cubic LaCrO_{3δ} are found to be monotonically closed by 1.13 eV in pristine and by around 0.62 eV in oxygenvacant 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 zerotemperature band gaps. 
Wednesday, March 16, 2022 3:36PM  3:48PM 
Q48.00004: SubPlanckian electron diffusion in a model of ultrastrong electronphonon coupling Calvin Pozderac, Brian Skinner The conjecture of the Planckian bound on transport implies a temperaturedependent lower bound on the electron diffusion constant. Motivated by this conjecture, we study a model of electron diffusion in the limit of ultrastrong electronphonon 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 subPlanckian diffusion. 
Wednesday, March 16, 2022 3:48PM  4:00PM 
Q48.00005: Impact of the transport formalism on the phononlimited carrier mobilities in semiconductors Romain Claes, Guillaume Brunin, Matteo Giantomassi, GianMarco Rignanese, Geoffroy Hautier Carrier mobility is an essential property in many different applications. Solar cells, thermoelectrics, transparent conductors or even lightemitting 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 lowcost 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 phononlimited mobility for semiconductors using different methodologies [13]. In this work, we present the latest developments in ABINIT regarding the calculation of the phononlimited mobility within the semiclassical Boltzmann transport formalism and results for new and stateofthe 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 firstprinciples 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 firstprinciples. We first discuss how semiclassical firstprinciples models are unable to capture the electronic transport properties of Bi_{2}Se_{3}, a narrowgap 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 firstprinciples model based on the Wigner distribution. Surprisingly, we find that Zener tunneling is not limited to lowenergy carriers, but occurs also between band subvalleys of energy larger than the band gap. Next, we introduce Phoebe, a new opensource software for computing thermoelectric properties by solving the electron and phonon Boltzmann equations. Phoebe computes electronphonon and phononphonon scattering properties from firstprinciples simulations, allowing a fully abinitio 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 lightmatter strong coupling Jaime AbadArredondo, Francisco José García Vidal, Antonio I FernándezDominguez Due to recent advances in the control of the quantum properties of collimated freeelectron 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 wavepacket and a hybrid photonicexcitonic 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 JaynesCummings polariton ladder of the cavityemitter system through both the freeelectron and photon spectra and demonstrate the power of modulated electrons as nearfield probes of lightmatter interactions in the strongcoupling regime. 
Wednesday, March 16, 2022 5:00PM  5:12PM 
Q48.00009: Automated computation of phononlimited carrier mobilities in semiconductors Guillaume Brunin, Romain Claes, Matteo Giantomassi, GianMarco Rignanese, Geoffroy Hautier Firstprinciples computations of phononlimited 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 twodimensional materials from firstprinciples Dhruv C Desai, Bahdan Zviazhynski, JinJian 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 firstprinciples method to study magnetotransport phenomena in materials by solving the Boltzmann transport equation (BTE) with abinitio electronphonon collisions in the presence of an external magnetic field [1]. We apply this approach to various semiconductors and twodimensional (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 LOTO 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 longwavelength limit, longitudinal polaroptical 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 LOTO 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 momenta^{1}. Using analytical models and densityfunctional perturbation theory in a newlyimplemented onedimensional 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 atomicchain, 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 readytouse 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 lowtemperature 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 SelfConsistent 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 MLFFaided stochastic method may open new paths for the study of quantum paraelectrics and phonon instabilities in large systems. 
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