Sharp Raman Anomalies and Broken Adiabaticity at a Pressure Induced Transition from Band to Topological Insulator inSb2Se3

Abstract

The non-trivial electronic topology of a topological insulator is so 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 2 g 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 non-adiabatic renormalization of phonons constitutes readily measurable bulk signatures of an ETT, which will facilitate efforts to develop topological insulators by modifying a band insulator.

Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide

“…In the intermediate state, vibrational phonon softening phenomenon in the Raman spectra has been studied extensively for other layered materials 39 , suggesting that it can be used as a clear signature for the electronic phase transition in the multilayered MoS 2 . The pressure-dependent Raman frequency increase was observed to be higher for the out-of-plane A 1g mode than that of the in-plane E 2g mode.…”

“…3d). It should be noted that in a recent report, a drop in the FWHM was also observed during a phase transition in Sb 2 Se 3 , a topological insulator that exhibits a metallic state at the surface 39 .…”

Raman anomalies as signatures of pressure induced electronic topological and structural transitions in black phosphorus: Experiments and theory

“…7(c)), which is in contrast to the earlier DFT study (within GGA and mBJ functional) where persistence of robust band crossing is reported after band inversion 30 . In an electronic topological transition the bandgap decreases with increasing pressure, closes at P c and then increases (opens up) with further increase in pressure 32 . We have plotted the bandgap of BP at Z-point (the point at which band inversion occurs) in the vicinity of critical pressure, which clearly shows bandgap reduces and then increases as a function of volume (Fig 2(b)) i.e., the bandgap exhibits a minimum value at P c1 and then increases.…”

Converting normal insulators into topological insulators via tuning orbital levels

“…A few approaches have been proposed and developed for the purpose. For example, topological phase transitions in normal insulators can be induced by manipulating the crystal lattice via external strain [10][11][12][13][14][15] and chemical doping/functionalization [16][17][18][19][20][21][22], or by tuning the electronic structure via electric field [23] and quantum confinement [24]. The general physical picture behind these approaches is either to tune the spin-orbit coupling (SOC) strength or to change the bonding strength of the normal insulators, so as to induce the band inversion required.…”