Pressure dependence of the band-gap energy in BiTeI

TL;DR

This study investigates how pressure affects the electronic band-gap of BiTeI, revealing a transition to a topological insulator state at a critical pressure where the gap closes, with implications for its structural and electronic properties.

Contribution

It provides a comparative analysis of semilocal and dispersion-corrected density-functional calculations on BiTeI under pressure, identifying the critical conditions for band-gap closure and topological transition.

Findings

Band-gap decreases with pressure, reaching zero at a critical point.

The critical pressure for gap closure aligns with a specific van der Waals gap width.

Both computational approaches predict similar trends despite differences in compressibility estimates.

Abstract

The evolution of the electronic structure of BiTeI, a layered semiconductor with a van der Waals gap, under compression is studied by employing semilocal and dispersion-corrected density-functional calculations. Comparative analysis of the results of these calculations shows that the band-gap energy of BiTeI decreases till it attains a minimum value of zero at a critical pressure, after which it increases again. The critical pressure corresponding to the closure of the band gap is calculated, at which BiTeI becomes a topological insulator. Comparison of the critical pressure to the pressure at which BiTeI undergoes a structural phase transition indicates that the closure of the band gap would not be hindered by a structural transformation. Moreover, the band-gap pressure coefficients of BiTeI are computed, and an expression of the critical pressure is devised in terms of these coefficients. Our findings indicate that the semilocal and dispersion-corrected approaches are in conflict about the compressibility of BiTeI, which result in overestimation and underestimation, respectively. Nevertheless, the effect of pressure on the atomic structure of BiTeI is found to be manifested primarily as the reduction of the width of the van der Waals gap according to both approaches, which also yield consistent predictions concerning the interlayer metallic bonding in BiTeI under compression. It is consequently shown that the calculated band-gap energies follow qualitatively and quantitatively the same trend within the two approximations employed here, and the transition to the zero-gap state occurs at the same critical width of the van der Waals gap.