Anisotropic atomic-structure related anomalous Hall resistance in few-layer black phosphorus

Abstract

Mono- (or few) layer black phosphorus (BP) is highly expected to be a next-generation two-dimensional (2D) atom-thin semiconductor. Compared with other 2D atom-thin layers, BP has a significantly anisotropic atomic structure, which can provide unique electronic, optical, and magnetic properties. Herein, we report the observation of B^2/3 magnetic-field (B) dependence of the Hall resistance with extremely small quantized levels in the low-B regime of the few-layer BP, which are associated with the anisotropic electronic structure confirmed by largely anisotropic hole mobilities. One of the qualitative interpretations for the B^2/3 dependence is the possible presence of a uniaxial Dirac spectrum (arising from a closed band gap caused by uniaxial stretch along the buckling armchair direction, which is occasionally introduced by a process for cutting and wire-bonding samples, confirmed by Raman spectroscopy) and its hybridization with a Schrödinger spectrum existing along a zigzag direction. The observed phenomena imply significant potential due to strong anisotropy of atom-thin (few-layer) BP, which is highly expected to open doors to novel physics and its application for innovative 2D atom-thin devices.