Electronic properties of thin films of tensile strained HgTe

TL;DR

This paper models the electronic properties of tensile strained HgTe thin films using an 8-band k·p approach, revealing how electrostatic effects influence their topological surface states and transport characteristics.

Contribution

It introduces a self-consistent microscopic model that accounts for gate field screening in strained HgTe thin films, refining the interpretation of experimental data.

Findings

Screening effects significantly impact the electronic structure of HgTe thin films.

A smaller dielectric constant (~6.5) better fits experimental observations.

The model alters previous interpretations of topological surface state behavior.

Abstract

Tensile strained bulk HgTe is a three-dimensional topological insulator. Because of the energetic position of its surface state Dirac points relative to its small bulk gap, the electronic properties of the relatively thin MBE-grown films used to study this material experimentally are quite sensitive to details of its electrostatic band-bending physics. We have used an 8-band $\mathbf{k} \cdot \mathbf{p}$ model to evaluate the gate voltage dependence of its thin-film two-dimensional subbands and related thermodynamic and transport properties in films with thicknesses between 30 and 70nm, accounting self-consistently for gate field screening by the topologically protected surface states and bulk state response. We comment on the effective dielectric constant that is appropriate in calculations of this type, arguing for a smaller value $\varepsilon_r$ $\approx$ 6.5 than is commonly used. Comparing with recent experiments, we find that our fully microscopic model of gate field screening alters the interpretation of some observations that have been used to characterize strained HgTe thin films.