Gate Switchable Transport and Optical Anisotropy in 90° Twisted Bilayer Black Phosphorus
(a) Structure of 90° twisted bilayer black phosphorus with top layer (red) and bottom layer (blue). (b) Hole effective mass along different directions under different electric fields. (c) Schematic of optical transitions from top two valence bands to conduction band under E field. (d) Oscillator strength of the two optical transitions as a function of direction of light polarization.
Discovery of a phenomenon of gate-voltage controlled, switchable anisotropy in the transport and optical properties of bilayer black phosphorus with an interlayer twist angle of 90°.
Significance and Impact
Findings advance fundamental understanding of stacked 2D crystals and point toward potential use of tunable anisotropy in them as a new degree of freedom for electronic and optoelectronic applications.
- Ab initio calculations show that, in 90° twisted bilayer black phosphorus, 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 electronic structure also leads to a switchable optical linear dichroism, where the polarization of the lowest-energy optical transitions is tunable by gating.