Quantum transport evidence of the boundary states and Lifshitz transition in Bi$_4$Br$_4$

TL;DR

This study investigates the quantum transport properties of Bi$_4$Br$_4$, revealing boundary states, surface state oscillations, and a Lifshitz transition, thus providing experimental evidence of its topological electronic characteristics.

Contribution

The paper provides the first experimental transport evidence of boundary states and Lifshitz transition in Bi$_4$Br$_4$, a high-order topological insulator.

Findings

Observation of 2D quantum oscillations from surface states.

Detection of boundary state contributions in magnetoresistance.

Identification of temperature-induced Lifshitz transition affecting electron concentration.

Abstract

The quasi-one-dimensional van der Waals compound Bi$_4$Br$_4$ was recently found to be a promising high-order topological insulator with exotic electronic states. In this paper, we study the electrical transport properties of Bi$_4$Br$_4$ bulk crystals. Two electron-type samples with different electron concentrations are investigated. Both samples have saturation resistivity behavior in low temperature. In the low-concentration sample, two-dimensional quantum oscillations are clearly observed in the magnetoresistance measurements, which are attributed to the band-bending-induced surface state on the (001) facet. In the high-concentration sample, the angular magnetoresistance exhibits two pairs of symmetrical sharp valleys with an angular difference close to the angle between the crystal planes (001) and (100). The additional valley can be explained by the contribution of the boundary states on the (100) facet. Besides, Hall measurements at low temperatures reveal an anomalous decrease of electron concentration with increasing temperature, which can be explained by the temperature-induced Lifshitz transition. These results shed light on the abundant surface and boundary state transport signals and the temperature-induced Lifshitz transition in Bi$_4$Br$_4$.