Observation and control of the weak topological insulator state in ZrTe5

TL;DR

This study visualizes the topological surface states of ZrTe5, a weak topological insulator candidate, revealing a quasi-1D band with spin-momentum locking and demonstrating strain-controlled topological phase transitions.

Contribution

First direct observation of topological surface states in ZrTe5 using spin and angle-resolved photoemission spectroscopy, showing strain-tunable topological phases.

Findings

Visualization of quasi-1D topological surface states with spin-momentum locking

Strain controls the transition between WTI and Dirac semimetal states

Identification of a highly directional spin-current in ZrTe5

Abstract

A quantum spin Hall insulator hosts topological states at the one-dimensional edge, along which backscattering by nonmagnetic impurities is strictly prohibited and dissipationless current flows. Its 3D analogue, a weak topological insulator (WTI), possesses similar quasi-1D topological states confined at side surfaces of crystals. The enhanced confinement could provide a route for dissipationless current and better advantages for applications relative to the widely studied strong topological insulators. However, the topological side surface is usually not cleavable and is thus hard to observe by angle-resolved photoemission spectroscopy (ARPES), which has hindered the revealing of the electronic properties of WTIs. Here, we visualize the topological surface states of the WTI candidate ZrTe5 for the first time by spin and angle-resolved photoemission spectroscopy: a quasi-1D band with spin-momentum locking was revealed on the side surface. We further demonstrate that the bulk band gap in ZrTe5 is controlled by strain to the crystal, realizing a more stabilized WTI state or an ideal Dirac semimetal state depending on the direction of the external strain. The highly directional spin-current and the tunable band gap we found in ZrTe5 will provide an excellent platform for applications.