Quantum transport properties in single crystals of α−Bi4I4

We report the magnetotransport properties of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Bi}}₄{\mathrm{I}}₄$ single crystals, which have a crystal structure similar to that of the quasi-one-dimensional topological insulator $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Bi}}₄{\mathrm{I}}₄$. 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 $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Bi}}₄{\mathrm{I}}₄$ 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 $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Bi}}₄{\mathrm{I}}₄$ in the future.