Unconventional transformation of spin Dirac phase across a topological quantum phase transition

TL;DR

This study uses photoemission spectroscopy to observe the evolution of surface states in a topological insulator during a quantum phase transition, revealing an exotic spin-momentum locked state in the trivial phase that mimics topological properties.

Contribution

It uncovers an unconventional, spin-momentum locked surface state in the trivial phase, providing new insights into the emergence of topological surface states during phase transitions.

Findings

Discovery of a gapped, spin-momentum locked surface state in the trivial phase

Surface states develop topological-like spin textures before the phase transition

Provides a new paradigm for understanding surface state formation in topological materials

Abstract

The topology of a topological material can be encoded in its surface states. These surface states can only be removed by a bulk topological quantum phase transition into a trivial phase. Here we use photoemission spectroscopy to image the formation of protected surface states in a topological insulator as we chemically tune the system through a topological transition. Surprisingly, we discover an exotic spin-momentum locked, gapped surface state in the trivial phase that shares many important properties with the actual topological surface state in anticipation of the change of topology. Using a spin-resolved measurement, we show that apart from a surface band-gap these states develop spin textures similar to the topological surface states well-before the transition. Our results offer a general paradigm for understanding how surface states in topological phases arise and are suggestive for future realizing Weyl arcs, condensed matter supersymmetry and other fascinating phenomena in the vicinity of topological quantum criticality.