Direct observation and temperature control of the surface Dirac gap in the topological crystalline insulator (Pb,Sn)Se

TL;DR

This study demonstrates temperature-induced gap opening in Dirac surface states of (Pb,Sn)Se topological crystalline insulators, enabling control over massless and massive topological states via temperature and composition adjustments.

Contribution

First experimental observation of temperature-driven Dirac gap opening in (Pb,Sn)Se TCI, establishing tunability of surface state mass through temperature and composition.

Findings

Temperature induces a gap in Dirac surface states.

Identified a boundary between massless and massive states.

Mapped the topological phase diagram with temperature and composition.

Abstract

Since the advent of topological insulators hosting symmetry-protected Dirac surface states, efforts have been made to gap these states in a controllable way. A new route to accomplish this was opened up by the discovery of topological crystalline insulators (TCIs) where the topological states are protected by real space crystal symmetries and thus prone to gap formation by structural changes of the lattice. Here, we show for the first time a temperature-driven gap opening in Dirac surface states within the TCI phase in (Pb,Sn)Se. By using angle-resolved photoelectron spectroscopy, the gap formation and mass acquisition is studied as a function of composition and temperature. The resulting observations lead to the addition of a temperature- and composition-dependent boundary between massless and massive Dirac states in the topological phase diagram for (Pb,Sn)Se (001). Overall, our results experimentally establish the possibility to tune between a massless and massive topological state on the surface of a topological system.