title: Sharp Raman anomalies and broken adiabaticity at a pressure induced transition from band to topological insulator in Sb2Se3.
abstract: The nontrivial electronic topology of a topological insulator is thus far known to display signatures in a robust metallic state at the surface. Here, we establish vibrational anomalies in Raman spectra of the bulk that signify changes in electronic topology: an E(g)(2) phonon softens unusually and its linewidth exhibits an asymmetric peak at the pressure induced electronic topological transition (ETT) in Sb(2)Se(3) crystal. Our first-principles calculations confirm the electronic transition from band to topological insulating state with reversal of parity of electronic bands passing through a metallic state at the ETT, but do not capture the phonon anomalies which involve breakdown of adiabatic approximation due to strongly coupled dynamics of phonons and electrons. Treating this within a four-band model of topological insulators, we elucidate how nonadiabatic renormalization of phonons constitutes readily measurable bulk signatures of an ETT, which will facilitate efforts to develop topological insulators by modifying a band insulator.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Achintya
authors.initials: A
authors.lastname: Bera
authors.forename: Koushik
authors.initials: K
authors.lastname: Pal
authors.forename: D V S
authors.initials: DV
authors.lastname: Muthu
authors.forename: Somaditya
authors.initials: S
authors.lastname: Sen
authors.forename: Prasenjit
authors.initials: P
authors.lastname: Guptasarma
authors.forename: U V
authors.initials: UV
authors.lastname: Waghmare
authors.forename: A K
authors.initials: AK
authors.lastname: Sood