Unconventional topological phase transition from semimetal to insulator in SnBi2Te4: Role of anomalous thermal expansion

TL;DR

This study reveals that SnBi2Te4 undergoes temperature-driven topological phase transitions from semimetal to insulator, driven by anomalous thermal expansion affecting its electronic structure, supported by combined theoretical and experimental evidence.

Contribution

It is the first comprehensive investigation showing temperature-induced topological phase transitions in SnBi2Te4, highlighting the role of anomalous thermal expansion in tuning topological phases.

Findings

SnBi2Te4 transitions from semimetal to insulator with increasing temperature.

Anomalous thermal expansion significantly influences the bulk band structure.

Surface states remain robust across the temperature range.

Abstract

We propose SnBi2Te4 to be a novel candidate material exhibiting temperature (T) mediated transitions between rich topological phases. From a combined theoretical and experimental studies, we find that SnBi2Te4 goes from a low-T topological semimetallic phase to a high-T (room temperature) topological insulating phase via an intermediate topological metallic phase. Single crystals of SnBi2Te4 are characterized by various experimental probes including Synchrotron based X-ray diffraction, magnetoresistance, Hall effect, Seebeck coefficient, magnetization and angle-resolved photoemission spectroscopy (ARPES). X-ray diffraction data confirms an anomalous thermal expansion of the unit cell volume below 100 K, which significantly affects the bulk band structure and hence the transport properties, as confirmed by our density functional theory calculations. Simulated surface states at 15 K agree fairly well with our ARPES data and are found to be robust with varying T. This indirectly supports the experimentally observed paramagnetic singularity in the entire T-range. The proposed coexistence of rich topological phases is a rare occurrence, yet paves a fertile ground to tune various topological phases in a material driven by structural distortion.