Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session LL06: V: Electrons, Phonons, Electron-Phonon Scattering and Phononics II |
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Sponsoring Units: DCOMP Chair: Pravinkumar Ghodake, Indian Institute of Technology Bombay Room: Virtual Room 6 |
Tuesday, March 21, 2023 5:00AM - 5:12AM |
LL06.00001: Chiral phonons in lattices with C4 symmetry Qianqian Wang Chiral phonons were initially proposed and further verified experimentally in two-dimensional (2D) hexagonal crystal lattices. Many intriguing features brought about by chiral phonons are attributed to the pseudoangular momenta which are associated with the threefold rotational symmetry of hexagonal lattices. Here, we go beyond the hexagonal crystals and investigate the chiral phonons in systems with fourfold rotational symmetry. We clarify the symmetry requirements for the emergence of chiral phonons in both 2D square lattices and three-dimensional tetragonal lattices. For two dimensions, the realization of C4 chiral phonons requires the breaking of time-reversal symmetry; while for three dimensions, they can exist on the C4-invariant path in a chiral tetragonal lattice. These phonons have the advantage that they can be more readily coupled with optical transitions, which facilitates their experimental detection. We demonstrate our idea via model analysis and first-principles calculations of concrete materials, including the MnAs monolayer and the α-cristobalite. Our work reveals chiral phonons beyond the hexagonal lattices and paves the way for further exploration of chiral phonon physics in square/tetragonal materials and metamaterials. |
Tuesday, March 21, 2023 5:12AM - 5:24AM |
LL06.00002: Anharmonic phonons from minimal symmetrized basis Ibrahim Buba Garba, Lorenzo Paulatto, Michele Casula Anharmonic phonon methods of computing phonon quasiparticles and interatomic force constants (FCs) at a finite temperature, such as the effective potential methods [1], [2], rely on expensive direct supercell method of computing phonons and subsequent fit to finite-temperature ab-initio forces. We present a method that relies on a highly efficient reciprocal-space representation that fully exploits symmetries to minimize the number of degrees of freedom. The method overcomes the limitations of the harmonic and quasiharmonic approximations by allowing efficient prediction of the temperature dependence of phonons, and hence accurately the thermal properties of materials while retaining the familiar quasi-particle representation. For test cases, such as ferroelectric oxide SrTiO3, our method provides converged phonons that are in good agreement with the experiment. |
Tuesday, March 21, 2023 5:24AM - 5:36AM |
LL06.00003: Resonant amplification of hydrodynamic temperature waves in graphite Michele Simoncelli Recent experiments have observed temperature waves in graphite, discussing how these appear when “normal” phonon scattering (which conserves phonons’ energy and crystal momentum) dominates over “umklapp” scattering (which conserves only energy). Under these conditions, the mesoscopic state of the system is described not only by temperature T (originating from the microscopic conservation of energy) but also from a drift velocity u (related to quasi conservation of momentum and bearing analogies to the velocity field in a fluid). The magnitude of these “hydrodynamic” phenomena is strongly affected by the relative strength of normal and umklapp scattering, and by the crystal’s purity, size, and shape; in practice such a magnitude is often weak and therefore measurement are challenging. Here we investigate from first principles the conditions determining the emergence and magnitude of temperature waves in graphite, also analyzing analogies and differences emerging from describing their evolution using Cattaneo’s equation [Comptes Rendus 247, 431(1958)] or the viscous heat equations [Phys. Rev. X 10, 011019 (2020)]. Finally, we show that temperature waves can be driven to resonance, thus the consequent amplification could facilitate their experimental detection. |
Tuesday, March 21, 2023 5:36AM - 5:48AM |
LL06.00004: When does the Tamura model of phonon-isotope scattering break down? Nakib H Protik, Claudia Draxl A standard approach to the phonon-isotope scattering problem is the Tamura model [1]. This non-self-consistent 1st Born approximation of the scattering T-matrix expansion is exact for the low energy phonons, and higher order perturbative corrections for the higher energy, dispersive acoustic phonons have been argued to be small [1]. To our knowledge, the validity of this approach for the optic phonons has not yet been demonstrated. In this talk, we compare the Tamura model to the ab initio computed non-perturbative phonon-isotope scattering T-matrix for a set of well-studied materials. We show under what conditions the Tamura model breaks down. |
Tuesday, March 21, 2023 5:48AM - 6:00AM |
LL06.00005: Revisiting the question of second sound in germanium Samuel Huberman, Jamal Abou Haibeh, Chuang Zhang, Qichen Song Recent experimental work, when combined with a macroscopic hyperbolic heat equation, claimed the observation of a type of second sound in germanium. However, a complete microscopic picture that captures the mechanism responsible for occurrence of second sound remains elusive. By directly solving the linearized phonon Boltzmann transport equation (LBTE), we take a step in addressing this missing piece. First, by performing an eigendecomposition of the full scattering matrix, we show that the conditions for driftless second sound are not satisfied. Second, by the application of Guyer’s criteria and inspection of the phonon-phonon scattering rates, we show that the conditions for drifting second sound are not satisfied. Furthermore, direct solutions to the LBTE for a frequency modulated heat source do not reveal the presence of an ‘other type’ of second sound. Finally, numerical solutions to the BTE under the relaxation time approximation (RTA) in the 1D frequency-domain thermoreflectance (1D-FDTR) experimental geometry demonstrate that phase lag alone is not a suitable experimental observable for inferring second sound. We conclude by discussing our own ongoing experimental work on germanium using pump-probe spectroscopy. |
Tuesday, March 21, 2023 6:00AM - 6:12AM |
LL06.00006: Excited singlet and triplet states of the negatively charged NV-center in diamond calculated using a variation density functional approach Hannes Jonsson, Aleksei Ivanov The first two excited singlet states and the first excited triplet state as well as the triplet ground state of the negatively charged NV-center in diamond have been calculated using a novel approach based on convergence to the corresponding saddle points on the electronic energy surface. The method makes use of direct optimization of the orbitals in a cell subject to periodic boundary conditions [1]. The PBE density functional is used with PAW representation of the inner electrons. After spin purification has been applied, the calculated energy differences between the states are found to be in remarkably close agreement with recent RPA calculations as well as a cluster calculation using a multiconfigurational approach [3]. The approach used here makes calculations of excited states in materials similar in computational effort as ground state DFT calculations. |
Tuesday, March 21, 2023 6:12AM - 6:24AM |
LL06.00007: First principles application of the Guyer criteria and heat pulse simulation for phonon hydrodynamics in fluorides and alkali hydrides Samuel Huberman, Jamal Abou Haibeh, Chuang Zhang Previous experimental studies have reported the wave-like transport of heat in a small number of crystalline solids. Such phenomena, referred to as 'second sound', is considered evidence for phonon hydrodynamics. In this work, we employ an ab-initio framework to study phonon hydrodynamics in fluorides and alkali hydrides crystals: sodium fluoride (NaF), lithium fluoride (LiF), lithium hydride (LiH), and sodium hydride (NaH). We first use Guyer's criteria as a guide to determine the regime window of phonon hydrodynamics in the temperature-length scale phase space. We then use an efficient numerical phonon BTE solver under the Callaway approximation to simulate practical experimental geometries. Based on these calculations, we observe the ballistic, hydrodynamic and diffusive phonon transport regimes for each of these four materials. Our calculations predict the existence of the second sound in NaF at a temperature of 15 K and a 8.3 mm characteristic length, consistent with a previous experimental observation [Phys. Rev. Lett. 25, 26 (1970) - Second Sound in NaF]. |
Tuesday, March 21, 2023 6:24AM - 6:36AM |
LL06.00008: Vibrational Modes in High-Configurational-Entropy Rocksalt Oxides Connor M Wilson, David Crandles, Ganesh Ramachandran Single-phase, cation-disordered rocksalt structure oxides such as Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O can be synthesized by annealing equimolar mixtures of five binary oxides to 1000°C and then quenching to room temperature. The resulting compounds have high configurational entropy, which may play a crucial role in stabilizing the rocksalt structure. In systems with translational symmetry, vibrational modes can be understood using a ‘phonon gas’ model. In disordered systems, this may have to be replaced by a threefold division into propagons, diffusons and locons. Initial ab initio structural relaxation of a 64-atom Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O supercell using Quantum ESPRESSO found a triclinic unit cell which disagrees with measured xray diffraction data. Additionally, ab initio calculations on 216-atom supercells resulted in unphysical, negative modes in the phonon density-of-states. These difficulties with density functional theory motivate a ‘toy model’ based on classical lattice dynamics (CLD). In this work, the CLD model is studied in Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O using the General Utility Lattice Program and compared with infrared and Raman spectra measurements. We propose that high-entropy oxides are a rich playground to study and probe phonon localization by calculating inverse participation ratios. |
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