Scanning tunneling microscopy and spectroscopy of twisted trilayer graphene

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to investigate twisted trilayer graphene, revealing multiple van Hove singularities and electronic symmetry breaking, highlighting the impact of twist angles on electronic properties.

Contribution

First systematic experimental analysis of twisted trilayer graphene showing multiple VHSs and electron-electron interactions affecting its electronic states.

Findings

Observation of two sets of VHSs from different twist angles

Detection of split VHSs indicating electron-electron interactions

Imaging of spatial symmetry breaking around VHSs

Abstract

Twist, as a simple and unique degree of freedom, could lead to enormous novel quantum phenomena in bilayer graphene. A small rotation angle introduces low-energy van Hove singularities (VHSs) approaching the Fermi level, which result in unusual correlated states in the bilayer graphene. It is reasonable to expect that the twist could also affect the electronic properties of few-layer graphene dramatically. However, such an issue has remained experimentally elusive. Here, by using scanning tunneling microscopy/spectroscopy (STM/STS), we systematically studied a twisted trilayer graphene (TTG) with two different small twist angles between adjacent layers. Two sets of VHSs originating from the two twist angles were observed in the TTG, indicating that the TTG could be simply regarded as a combination of two different twisted bilayer graphene. By using high-resolution STS, we observed split of the VHSs and directly imaged spatial symmetry breaking of electronic states around the VHSs. These results suggest that electron-electron interactions play an important role in affecting the electronic properties of graphene systems with low-energy VHSs.