Gate Switchable Transport and Optical Anisotropy in 90{\deg} Twisted Bilayer Black Phosphorus

TL;DR

This study predicts that gating can dynamically control the electronic and optical anisotropy in 90-degree twisted bilayer black phosphorus, enabling tunable properties for electronic and photonic applications.

Contribution

It introduces the concept of gate-tunable anisotropy in twisted bilayer black phosphorus, a feature not present in conventional bulk materials.

Findings

Gate voltage induces a 30-fold change in hole effective mass along different axes.

The anisotropy axes can be exchanged by reversing the gate voltage.

Optical linear dichroism becomes switchable via gating.

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{\deg}, 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.