Quantum transport evidence of boundary states and Lifshitz transition in Bi4Br4

The quasi-one-dimensional van der Waals compound Bi4Br4 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 Bi4Br4 bulk crystals. Two electron-type samples with different electron concentrations are investigated. Both samples exhibit a saturation behavior of resistivity 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) surface. 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 boundary state transport signals and the temperature-induced Lifshitz transition in Bi4Br4.