Gate-Tunable Transport in Quasi-One-Dimensional α-Bi<sub>4</sub>I<sub>4</sub> Field Effect Transistors
Yulu Liu, Ruoyu Chen, Zheneng Zhang, Marc Bockrath, Chun Ning Lau, Yan-Feng Zhou, Chiho Yoon, Li Sheng, Xiaoyuan Liu, Nikhil Dhale, Bing Lv, Fan Zhang, Kenji Watanabe, Takashi Taniguchi, Jianwei Huang, Ming Yi, Ji Seop Oh, R. J. Birgeneau
Abstract
Bi4I4 belongs to a novel family of quasi-one-dimensional (1D) topological insulators (TIs). While its β phase was demonstrated to be a prototypical weak TI, the α phase, long thought to be a trivial insulator, was recently predicted to be a rare higher order TI. Here, we report the first gate tunable transport together with evidence for unconventional band topology in exfoliated α-Bi4I4 field effect transistors. We observe a Dirac-like longitudinal resistance peak and a sign change in the Hall resistance; their temperature dependences suggest competing transport mechanisms: a hole-doped insulating bulk and one or more gate-tunable ambipolar boundary channels. Our combined transport, photoemission, and theoretical results indicate that the gate-tunable channels likely arise from novel gapped side surface states, two-dimensional (2D) TI in the bottommost layer, and/or helical hinge states of the upper layers. Markedly, a gate-tunable supercurrent is observed in an α-Bi4I4 Josephson junction, underscoring the potential of these boundary channels to mediate topological superconductivity.