Massive and topological surface states in tensile strained HgTe

TL;DR

This study demonstrates well-developed topological surface states in tensile strained HgTe through magneto-transport measurements, revealing coexistence of n-type topological states and p-type Volkov-Pankratov states, with implications for topological insulator transport.

Contribution

The paper provides experimental evidence of topological surface states in strained HgTe and identifies the role of Volkov-Pankratov states in p-type transport, expanding understanding of topological insulator surface phenomena.

Findings

Hall quantization confirms surface state conduction

p-type transport arises from Volkov-Pankratov states

Coexistence of n- and p-type states at specific gate voltages

Abstract

Magneto-transport measurements on gated high mobility heterostructures containing a 60 nm layer of tensile strained HgTe, a three-dimensional topological insulator, show well-developed Hall quantization from surface states both in the n- as well as in the p-type regime. While the n-type behavior is due to transport in the topological surface state of the material, we find from 8-orbital k.p calculations that the p-type transport results from massive Volkov-Pankratov states. Their formation prevents the Dirac point and thus the p-conducting topological surface state from being accessible in transport experiments. This interpretation is supported by low-field magneto-transport experiments demonstrating the coexistence of n-conducting topological surface states and p-conducting Volkov-Pankratov states at the relevant gate voltages.