Quantum transport properties in single crystals of alpha-Bi4I4

We report the magnetotransport properties of alpha-Bi4I4 single crystals, which have a crystal structure similar to that of the quasi-one-dimensional topological insulator beta-Bi4I4. Prominent Shubnikov-de Hass oscillations and weak antilocalization effect are observed in all measured samples. The angular-dependent magnetoresistance indicates that the behavior of Shubnikov-de Hass oscillations is two-dimensional (2D) in n-type samples, while it is three-dimensional (3D) in p-type samples. First-principles calculations show that the n-type samples have a 2D Fermi surface, while the p-type samples have a 3D Fermi surface. Considering the similar carrier density and mobility, we infer that the transport behaviors in both types of samples come from bulk electron contributions. In addition, a large negative magnetoresistance with a transverse configuration is observed in the n-type sample A1. All the results indicate that alpha-Bi4I4 is an important material platform for investigation of novel and interesting phenomena. Our work may also provide important references for studying the topological surface transport properties in beta-Bi4I4 in the future.