title: Gate Switchable Transport and Optical Anisotropy in 90° Twisted Bilayer Black Phosphorus.
abstract: Anisotropy describes the directional dependence of a material's properties such as transport and optical response. In conventional bulk materials, anisotropy is intrinsically related to the crystal structure and thus not tunable by the gating techniques used in modern electronics. Here we show that, in bilayer black phosphorus with an interlayer twist angle of 90°, the anisotropy of its electronic structure and optical transitions is tunable by gating. Using first-principles calculations, we predict that a laboratory-accessible gate voltage can induce a hole effective mass that is 30 times larger along one Cartesian axis than along the other axis, and the two axes can be exchanged by flipping the sign of the gate voltage. This gate-controllable band structure also leads to a switchable optical linear dichroism, where the polarization of the lowest-energy optical transitions (absorption or luminescence) is tunable by gating. Thus, anisotropy is a tunable degree of freedom in twisted bilayer black phosphorus.
authors.affiliation: Department of Physics, University of California at Berkeley , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Ting
authors.initials: T
authors.lastname: Cao
authors.affiliation: Department of Physics, University of California at Berkeley , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Zhenglu
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Physics, University of California at Berkeley , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Diana Y
authors.initials: DY
authors.lastname: Qiu
authors.affiliation: Department of Physics, University of California at Berkeley , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Louie
keywords: 2D materials; black phosphorus; electron transport; gate switchable anisotropy; optical dichroism