Strongly Enhanced Mass Anisotropy in Monolayer Phosphorene and Field Tunability

Phosphorene has attracted extensive research interest due to its anisotropic properties with rich tunabilities such as strongly layer-dependent and field-tunable band gaps. Revealing how the electronic structure evolves down to monolayer is critical for understanding its anisotropic properties and field tunability. Here, we report the hitherto unexplored electronic structure of monolayer phosphorene, as well as field tunability in few-layer phosphorene. A strongly enhanced mass anisotropy is observed in monolayer phosphorene, which clearly distinguishes it from bilayer and thicker flakes. Moreover, by introducing an external electric field upon doping, modifications of the mass anisotropy and energy spacing between subbands in few-layer phosphorene are further revealed. Our work reveals the unique electronic structure of monolayer phosphorene, highlighting the critical roles of interlayer coupling as well as external electric field in tailoring the band parameters in phosphorene.