Electric Field Tunable Band Gap in Commensurate Twisted Bilayer Graphene

TL;DR

This paper demonstrates that sublattice odd commensurate twisted bilayer graphene exhibits a tunable band gap via electric fields in the terahertz range, with lower energy scales and accessible strong-field regimes compared to Bernal bilayer graphene.

Contribution

It reveals that C-TBG's band gap can be electrically tuned in the terahertz range and introduces a method to measure interlayer coherence energy through optical conductivity.

Findings

C-TBG exhibits a tunable band gap in the terahertz range.

Lower energy scales in C-TBG make strong-field regimes more accessible.

Interlayer coherence energy can be experimentally determined from optical conductivity.

Abstract

Bernal bilayer graphene exhibits a band gap that is tunable through the infrared with an electric field. We show that sublattice odd commensurate twisted bilayer graphene (C-TBG) exhibits a band gap that is tunable through the terahertz with an electric field. We show that from the perspective of terahertz optics the sublattice odd and even forms of C-TBG are "inflated" versions of Bernal and AA stacked bilayer graphene respectively with energy scales reduced by a factor of 110 for the 21.79 degree commensurate unit cell. This lower energy scale is accompanied by a correspondingly smaller gate voltage, which means that the strong-field regime is more easily accessible than in the Bernal case. Finally, we show that the interlayer coherence energy is a directly accessible experimental quantity through the position of a power-law divergence in the optical conductivity.