Correlation effects on a topological insulator at finite temperatures

TL;DR

This paper investigates how local Coulomb interactions influence the electronic properties of topological band insulators at finite temperatures, revealing a first-order quantum phase transition and strong temperature-dependent effects on spin Hall conductivity.

Contribution

It provides a detailed analysis of correlation effects on TBIs using dynamical mean field theory, highlighting the nature of the phase transition and the behavior of the spectral gap.

Findings

Correlation reduces the spectral gap via renormalization.

The TBI to trivial Mott insulator transition is first order with hysteresis.

Spectral gap remains open at the transition.

Abstract

We analyze the effects of the local Coulomb interaction on a topological band insulator (TBI) by applying the dynamical mean field theory to a generalized Bernevig-Hughes-Zhang model having electron correlations. It is elucidated how the correlation effects modify electronic properties in the TBI phase at finite temperatures. In particular, the band inversion character of the TBI inevitably leads to the large reduction of the spectral gap via the renormalization effect, which results in the strong temperature-dependence of the spin Hall conductivity. We clarify that a quantum phase transition from the TBI to a trivial Mott insulator, if it is nonmagnetic, is of first order with a hysteresis. This is confirmed via the interaction dependence of the double occupancy and the spectral function. A magnetic instability is also addressed. All these results imply that the spectral gap does not close at the transition.