Gate tunable optical absorption and band structure of twisted bilayer graphene

TL;DR

This study demonstrates how electrical gating can significantly modify the band structure and optical absorption properties of twisted bilayer graphene, enabling tunable optoelectronic applications.

Contribution

It reveals universal, gating-induced non-rigid band structure modifications in twisted bilayer graphene and proposes their potential for device engineering.

Findings

Observation of splitting in inter-band absorption steps

Shift of van Hove singularity transition peaks

Emergence of strong intra-band transitions

Abstract

We report the infrared transmission measurement on electrically gated twisted bilayer graphene. The optical absorption spectrum clearly manifests the dramatic changes such as the splitting of inter-linear-band absorption step, the shift of inter-van Hove singularity transition peak, and the emergence of very strong intra-valence (intra-conduction) band transition. These anomalous optical behaviors demonstrate consistently the non-rigid band structure modification created by the ion-gel gating through the layer-dependent Coulomb screening. We propose that this screening-driven band modification is an universal phenomenon that persists to other bilayer crystals in general, establishing the electrical gating as a versatile technique to engineer the band structures and to create new types of optical absorptions that can be exploited in electro-optical device application.