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Electric-field tunable Dirac semimetal state in phosphorene thin films

We study the electric-field tunable electronic properties of phosphorene thin films, using the framework of density functional theory. We show that phosphorene thin films offer a versatile material platform to study two dimensional Dirac fermions on application of a transverse electric field. Increasing the strength of the transverse electric field beyond a certain critical value in phosphorene leads to the formation of two symmetry protected gapless Dirac fermions states with anisotropic energy dispersion. The spin-orbit coupling splits each of these Dirac state into two spin- polarized Dirac cones which are also protected by non-symmorphic crystal symmetries. Our study shows that the position as well as the carrier velocity of the spin polarized Dirac cone states can be controlled by the strength of the external electric field.