Quantum transport properties of beta-Bi4I4 near and well beyond the extreme quantum limit

TL;DR

This study investigates the magneto-transport properties of beta-Bi4I4, revealing quantum oscillations, a metal-insulator transition in the extreme quantum limit, and evidence of strong electron-electron interactions and magnetic freeze-out effects.

Contribution

It provides detailed experimental analysis of beta-Bi4I4's quantum transport behavior near and beyond the extreme quantum limit, highlighting its potential as a 3D topological system for exotic quantum phases.

Findings

Observation of Shubnikov-De Haas oscillations indicating a convex Fermi surface

Identification of a metal-insulator transition with a large critical exponent in high magnetic fields

Evidence of magnetic freeze-out effect with exponential increase in resistivity

Abstract

We have investigated the magneto-transport properties of beta-Bi4I4 bulk crystal, which was recently theoretically proposed and experimentally demonstrated to be a topological insulator. At low temperature T and magnetic field B, a series of Shubnikov-De Haas(SdH) oscillations are observed on the magnetoresistivity (MR). The detailed analysis reveals a light cyclotron mass of 0.1 me, and the field angle dependence of MR reveals that the SdH oscillations originate from a convex Fermi surface. In the extreme quantum limit (EQL) region, there is a metal-insulator transition occurring soon after the EQL. We perform the scaling analysis, and all the isotherms fall onto a universal scaling with a fitted critical exponent of 6.5. The enormous value of critical exponent implies this insulating quantum phase originated from strong electron-electron interactions in high fields. However, in the far end of EQL, both the longitudinal and Hall resistivity increase exponentially with B, and the temperature dependence of the MR reveals an energy gap induced by the high magnetic field, signifying a magnetic freeze-out effect. Our findings indicate that bulk beta-Bi4I4 is an excellent candidate for a 3D topological system for exploring EQL physics and relevant exotic quantum phases.