# 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.

## Key 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.

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Source: https://tomesphere.com/paper/2302.14228