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.
Highlights
In the family of topological materials, semimetals have an important place in the study of topological order because they exhibit topologically protected surface states [1], an anomalous bulk transport phenomenon known as the “quantum anomaly” [2, 3], diversified classifications like nodal rings and lines [4,5,6], and Weyl and Dirac points [7,8,9,10,11], and they serve as a platform for obtaining various other topological states, such as topological insulators [12] and Chern insulators [13]
We show that the phonon spectrum of multiple noncentrosymmetric perovskites can host three types of topological states—topological nodal rings, nodal lines, and Weyl points— suggesting that topological phonons are pervasive in different structural phases of oxide perovskites
Using the tetragonal BaTiO3 phase as a prototype, we show that all these types of topological phonon emerge simultaneously when this phase is stabilized by photoexcitation
Summary
In the family of topological materials, semimetals have an important place in the study of topological order because they exhibit topologically protected surface states [1], an anomalous bulk transport phenomenon known as the “quantum anomaly” [2, 3], diversified classifications like nodal rings and lines [4,5,6], and Weyl and Dirac points [7,8,9,10,11], and they serve as a platform for obtaining various other topological states, such as topological (crystalline) insulators [12] and Chern insulators [13]. Topological order can be controlled with the photoexcited carrier density, driving topological transitions without any associated structural phase change, including the creation and annihilation of Weyl phonons and switching between nodal-ring and nodal-line phonons.
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