Persistence of structural distortion and bulk band Rashba splitting in SnTe above its ferroelectric critical temperature

TL;DR

This study reveals that the bulk Rashba splitting in SnTe persists above its ferroelectric transition temperature, indicating local dipole fluctuations and challenging previous claims of topological surface states at the surface.

Contribution

It demonstrates the persistence of bulk Rashba splitting above the ferroelectric critical temperature in SnTe, suggesting an order-disorder transition and refuting the existence of topological surface states at the surface.

Findings

Bulk Rashba splitting persists up to room temperature.

Evidence supports an order-disorder phase transition with local dipole fluctuations.

No topological surface state occurs at the (111) surface of SnTe.

Abstract

The ferroelectric semiconductor $\alpha$-SnTe has been regarded as a topological crystalline insulator and the dispersion of its surface states has been intensively measured with angle-resolved photoemission spectroscopy (ARPES) over the last decade. However, much less attention has been given to the impact of the ferroelectric transition on its electronic structure, and in particular on its bulk states. Here, we investigate the low-energy electronic structure of $\alpha$-SnTe with ARPES and follow the evolution of the bulk-state Rashba splitting as a function of temperature, across its ferroelectric critical temperature of about $T_c\sim 110$ K. Unexpectedly, we observe a persistent band splitting up to room temperature, which is consistent with an order-disorder contribution to the phase transition that requires the presence of fluctuating local dipoles above $T_c$. We conclude that no topological surface state can occur at the (111) surface of SnTe, at odds with recent literature.