1303.1291 (Achintya Bera et al.)

Sharp Raman Anomalies and Broken Adiabaticity at a Pressure Induced
Transition from Band to Topological Insulator in Sb2Se3    [PDF]

Achintya Bera, Koushik Pal, D. V. S. Muthu, Somaditya Sen, Prasenjit Guptasarma, U. V. Waghmare, A. K. Sood

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 E2 g phonon softens unusually and its linewidth exhibits an asymmetric peak at the pressure induced electronic topological transition (ETT) in Sb2Se3 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.

View original: http://arxiv.org/abs/1303.1291