Nano-photocurrent mapping of local electronic structure in twisted bilayer graphene

TL;DR

This study introduces a nano-photocurrent and infrared nanoscopy technique to map local electronic structures in twisted bilayer graphene at nanometer scales, revealing twist-angle domains and electronic inhomogeneities.

Contribution

It presents a novel combined nano-photocurrent and infrared nanoscopy method for high-resolution mapping of electronic properties in twisted bilayer graphene.

Findings

Photocurrent sign changes with local superlattice density of states.

Identification of twist-angle domains via photo-thermoelectric effect.

Infrared nano-imaging shows twist-angle dependent interband transitions.

Abstract

We report a combined nano-photocurrent and infrared nanoscopy study of twisted bilayer graphene (TBG) enabling access to the local electronic phenomena at length scales as short as 20 nm. We show that the photocurrent changes sign at carrier densities tracking the local superlattice density of states of TBG. We use this property to identify domains of varying local twist angle by local photo-thermoelectric effect. Consistent with the photocurrent study, infrared nano-imaging experiments reveal optical conductivity features dominated by twist-angle dependent interband transitions. Our results provide a fast and robust method for mapping the electronic structure of TBG and suggest that similar methods can be broadly applied to probe electronic inhomogeneities of moir\'e superlattices in other van der Waals heterostructures.