Temperature-induced topological phase transition in HgTe quantum wells

TL;DR

This study demonstrates a temperature-driven topological phase transition in HgTe quantum wells, showing how the band structure changes with temperature and identifying the critical point where the phase transition occurs.

Contribution

First direct observation of a temperature-induced topological phase transition in HgTe quantum wells through Landau level measurements.

Findings

Identification of the critical temperature $T_c$ where the topological phase transition occurs.

Observation of the crossing of zero-mode Landau levels at the critical magnetic field.

Evidence of a trivial gap opening above the critical temperature.

Abstract

We report a direct observation of temperature-induced topological phase transition between trivial and topological insulator in HgTe quantum well. By using a gated Hall bar device, we measure and represent Landau levels in fan charts at different temperatures and we follow the temperature evolution of a peculiar pair of "zero-mode" Landau levels, which split from the edge of electron-like and hole-like subbands. Their crossing at critical magnetic field $B_c$ is a characteristic of inverted band structure in the quantum well. By measuring the temperature dependence of $B_c$, we directly extract the critical temperature $T_c$, at which the bulk band-gap vanishes and the topological phase transition occurs. Above this critical temperature, the opening of a trivial gap is clearly observed.