Structural and electronic signatures of strain-tunable marginally twisted bilayer graphene

TL;DR

This study uses scanning tunneling microscopy and tight-binding calculations to explore how strain influences the structural and electronic properties of marginally twisted bilayer graphene, revealing strain-controlled domain wall states.

Contribution

It provides the first detailed experimental and theoretical analysis of strain-induced domain wall transformations in marginally twisted bilayer graphene.

Findings

AA regions show localized electronic states with spectral peaks.

AB regions exhibit uniform spectral peaks indicating electronic homogeneity.

Two types of strain-induced domain walls identified and characterized.

Abstract

Marginally twisted bilayer graphene having small twist angles is predicted to exhibit unique structural and electronic properties, though experimental characterization remains limited. Using scanning tunneling microscopy, we investigate such systems with twist angles of 0.06^{\circ}-0.35^{\circ}. AA-stacked regions reveal a pronounced tunneling spectral peak signifying highly localized electronic states. Conversely, AB domains display uniform multiple spectral peaks, indicative of strong lattice reconstruction and enhanced electronic homogeneity. We identify two distinct strain-induced domain walls: one exhibits a sharp -120 meV spectral peak (shear type), while the other shows distinct spectral characteristics (mixed shear-tensile type). Tight-binding calculations verify strain-driven transformations of both domain wall types and confirm direct observation of strain-mediated domain wall transitions. These results elucidate the electronic structure of marginally twisted bilayer graphene and establish strain as a control parameter for domain wall states.