Anomalous spin-momentum locked two-dimensional states in the vicinity of a topological phase transition

TL;DR

This study uses spin-resolved photoemission spectroscopy to discover anomalous spin-momentum locked two-dimensional states near the topological phase transition in BiTl(S1-xSex)2, revealing precursor states on the trivial side.

Contribution

It reports the observation of spin-momentum locked 2D states near the topological transition, a phenomenon not previously documented in this material system.

Findings

Spin-momentum locked 2D states are observed on the trivial side of the transition.

These states exhibit helical spin textures similar to topological insulator surfaces.

The states are prominent only near the critical composition, indicating a link to the phase transition.

Abstract

We perform spin-resolved and spin-integrated angle-resolved photoemission spectroscopy measurements on a series of compositions in the BiTl(S1-xSex)2 system, focusing on x-values in the vicinity of the critical point for the topological phase transition (the band inversion composition). We observe quasi two dimensional (2D) states on the outer boundary of the bulk electronic bands in the trivial side (non-inverted regime) of the transition. Systematic spin-sensitive measurements reveal that the observed 2D states are spin-momentum locked, whose spin texture resembles the helical spin texture on the surface of a topological insulator. These anomalous states are observed to be only prominent near the critical point, thus are possibly related to strong precursor states of topological phase transition near the relaxed surface.