A field-induced reentrant insulator state of a gap-closed topological insulator (Bi_{1-x}Sb_x) in quantum-limit states

TL;DR

This study reveals a reentrant insulator phase in a topological insulator under high magnetic fields, suggesting the emergence of an excitonic insulator driven by many-body interactions in quantum-limit states.

Contribution

It demonstrates the realization of a reentrant insulator state in a topological insulator through magnetic field tuning, indicating possible excitonic insulator formation in extreme quantum conditions.

Findings

Observation of a reentrant insulator state at high magnetic fields

Evidence suggesting many-body effects drive the phase transition

Potential identification of an excitonic insulator phase

Abstract

In the extreme quantum limit states under high magnetic fields, enhanced electronic correlation effects can stabilize anomalous quantum states. Using band-tuning with a magnetic field, we realized a spin-polarized quantum limit state in the field-induced semimetallic phase of a topological insulator Bi_{1-x}Sb_x. Further increase in the field injects more electrons and holes to this state and results in an unexpected reentrant insulator state in this topological semimetallic state. A single-particle picture cannot explain this reentrant insulator state, reminiscent of phase transitions due to many-body effects. Estimates of the binding energy and spacing of electron-hole pairs and the thermal de Broglie wavelength indicate that Bi_{1-x}Sb_x may host the excitonic insulator phase in this extreme environment.