Scanning tunneling microscopy and spectroscopy of nanoscale twisted bilayer graphene

TL;DR

This study uses scanning tunneling microscopy to investigate the structure and electronic properties of nanoscale twisted bilayer graphene, revealing how quantum confinement and translational symmetry breaking influence its low-energy electronic features.

Contribution

It provides the first detailed experimental analysis of nanoscale TBG's electronic properties, highlighting the effects of quantum confinement and symmetry breaking.

Findings

Low-energy electronic properties are strongly affected by translational symmetry breaking.

Electronic properties above the van Hove singularities are nearly unaffected by quantum confinement.

Nanoscale TBG exhibits distinct electronic behavior compared to larger or bulk samples.

Abstract

Nanoscale twisted bilayer graphene (TBG) is quite instable and will change its structure to Bernal (or AB-stacking) bilayer with a much lower energy. Therefore, the lack of nanoscale TBG makes its electronic properties not accessible in experiment up to now. In this work, a special confined TBG is obtained in the overlaid area of two continuous misoriented graphene sheets. The width of the confined region of the TBG changes gradually from about 22 nm to 0 nm. By using scanning tunnelling microscopy, we studied carefully the structure and the electronic properties of the nanoscale TBG. Our results indicate that the low-energy electronic properties, including twist-induced van Hove singularities (VHSs) and spatial modulation of local density-of-state, are strongly affected by the translational symmetry breaking of the nanoscale TBG. Whereas, the electronic properties above the energy of the VHSs are almost not influenced by the quantum confinement even when the width of the TBG is reduced to only a single moire spot.