Nanofabrication and transport studies of Quasi-one-dimensional Topological Insulators Bismuth halides

Bismuth halides Bi4X4 (X = Br, I) constitute a family of quasi-one-dimensional (1D) topological insulators (TIs) that promise advantages such as multiple cleavage planes, strain-induced phase transitions and hosting of helical hinge modes. Depending on different combinations of halogen atoms, members of the bismuth halides family can exhibit distinct topological properties, ranging from a weak topological insulator to a higher order topological insulator. To-date, studies of the transport properties of Bi4X4 materials are still scarce. Here, using Bi4X4 single crystals, we are able to exfoliate and fabricate hexagonal boron nitride encapsulated thin layer Bi4X4 field effect transistors, and investigate their transport behavior as a function of temperature and charge density. We find evidence of gate tunable surface states in Bi4I4 and one-dimensional transport channels in Bi4Br4.