Surface of black phosphorus: a playground for tunable electronic states and interactions

Black phosphorus (BP)has attracted considerable interest as a two-dimensional semiconductor because of its high carrier mobility and unique anisotropy. The surface of BP has recently been demonstrated to host a variety of emergent phenomena, including an anisotropic Dirac semimetal state, a dipole liquid phase, and even strongly correlated effects. In this Perspective, we first summarize the electronic band structure of BP, with an emphasis on the surface resonance bands that experience tunable electronic reconstruction. We address the critical role of surface resonance bands in the screening of an external electric field. Around surface impurities, charging phenomena reveal reduced screening and spatially inhomogeneous electron localization, which invites an interplay between localization, electronic reconstruction, and correlation. We propose the surface of BP as a versatile playground for tunable electronic states and interactions, where many open questions and interesting directions remain to be explored.