title: Quantum-confinement and Structural Anisotropy result in Electrically-Tunable Dirac Cone in Few-layer Black Phosphorous.
abstract: Two-dimensional (2D) materials are well-known to exhibit interesting phenomena due to quantum confinement. Here, we show that quantum confinement, together with structural anisotropy, result in an electric-field-tunable Dirac cone in 2D black phosphorus. Using density functional theory calculations, we find that an electric field, E ext, applied normal to a 2D black phosphorus thin film, can reduce the direct band gap of few-layer black phosphorus, resulting in an insulator-to-metal transition at a critical field, Ec. Increasing E ext beyond Ec can induce a Dirac cone in the system, provided the black phosphorus film is sufficiently thin. The electric field strength can tune the position of the Dirac cone and the Dirac-Fermi velocities, the latter being similar in magnitude to that in graphene. We show that the Dirac cone arises from an anisotropic interaction term between the frontier orbitals that are spatially separated due to the applied field, on different halves of the 2D slab. When this interaction term becomes vanishingly small for thicker films, the Dirac cone can no longer be induced. Spin-orbit coupling can gap out the Dirac cone at certain electric fields; however, a further increase in field strength reduces the spin-orbit-induced gap, eventually resulting in a topological-insulator-to-Dirac-semimetal transition.
authors.affiliation: Department of Physics, Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117551.
authors.forename: Kapildeb
authors.initials: K
authors.lastname: Dolui
authors.affiliation: 1] Department of Physics, Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117551 [2] Institute of High Performance Computing, 1 Fusionopolis Way, # 16-16 Connexis, Singapore 138632.
authors.forename: Su Ying
authors.initials: SY
authors.lastname: Quek