Topological phonons in oxide perovskites controlled by light

Abstract

Perovskite oxides exhibit a rich variety of structural phases hosting different physical phenomena that generate multiple technological applications. We find that topological phonons—nodal rings, nodal lines, and Weyl points—are ubiquitous in oxide perovskites in terms of structures (tetragonal, orthorhombic, and rhombohedral), compounds (BaTiO3, PbTiO3, and SrTiO3), and external conditions (photoexcitation, strain, and temperature). In particular, in the tetragonal phase of these compounds, all types of topological phonons can simultaneously emerge when stabilized by photoexcitation, whereas the tetragonal phase stabilized by thermal fluctuations only hosts a more limited set of topological phonon states. In addition, we find that the photoexcited carrier concentration can be used to tune the topological phonon states and induce topological transitions even without associated structural phase changes. Overall, we propose oxide perovskites as a versatile platform in which to study topological phonons and their manipulation with light.

Unique surface-state connection between Weyl and nodal ring fermions in ferromagnetic material Cs2MoCl6

“…We also show that how the HSSs connect the projection of the nodal ring and the curvature of HSSs depend sensitively on the energy. Such unique surface-state connection also appear in several previous studies, yet lack of discussion [22][23][24][25][26]. Our results show that the connection pattern of the surface states is surface-dependent for systems with both Weyl and node-ring fermions, and it is universal for systems with/without considering SOC and T symmetry.…”

“…We notice that such unique surface-state connection behavior can be found in other materials with different symmetries, such as in the electronic band structure of FM HgCr 2 Se 4 (with SOC and without T ) [24], the electronic band structure of FM double perovskites (Ba 2 N aOsO 6 , Sr 2 SrOsO 6 , Ba 2 ZnReO 6 , Ba 2 M gReO 6 , and Ba 2 CdReO 6 , with SOC and without T ) [22,23], and the phonon band structure of oxide perovskites (BaT iO 3 , P bT iO 3 , without SOC and with T ) [26]. However, none of those works discuss on the connection of the unique surface states, and they mainly focus on the topology of the bulk bands.…”

Phonons as a platform for non-Abelian braiding and its manifestation in layered silicates

“…We further show that the evolution of Raman peaks can be used to track the band inversions and the accompanying braiding process, providing a clear experimental signature to identify multi-gap topology in real materials. Interest in the topological features of phonon bands has recently grown [29][30][31][32][33][34][35][36][37][38][39][40] , but for single-gap topology, phonons have traditionally received less attention than electrons. The bosonic nature of phonons should make them the prime platform for the study of multi-gap topology.…”

Effect of Nonequilibrium Transient Electronic Structures on Lattice Stability in Metals: Density Functional Theory Calculations

“…Phonon dispersion with quasi-harmonic approximation might not be persuasive, especially for cases far away from equilibrium. Focusing on the crystal instability and phonon hardening [46,51,65,[69][70][71] cases, we plotted the potential energy surface (PES) of Al and Cu in the normal coordinates for the transverse acoustic (TA) and longitudinal acoustic (LA) modes at the high-symmetry point L( 12 , 1 2 , 1 2 ) in the first Brillouin zone to include anharmonicity effect. The scaling factor Q 1 of the lowest TA mode and the scaling factor Q 2 of the LA mode are applied in the calculation, and the PES is a function of scaled coordinates E = E(Q 1 , Q 2 ); we do not show the second-lowest TA mode because it is degenerate with the lowest TA mode.…”