Topologically Protected Helical States in Minimally Twisted Bilayer Graphene

TL;DR

This paper demonstrates the experimental realization of topologically protected helical states in minimally twisted bilayer graphene, revealing their potential for robust electronic applications through scanning tunneling spectroscopy.

Contribution

It provides the first direct observation of TPH states in minimally twisted bilayer graphene using scanning tunneling spectroscopy.

Findings

TPH states observed on domain walls in twisted bilayer graphene

TPH states only appear when AB and BA regions are gapped

Method enables flexible construction of TPH state networks

Abstract

In minimally twisted bilayer graphene, a moir{\'e} pattern consisting of AB and BA stacking regions separated by domain walls forms. These domain walls are predicted to support counterpropogating topologically protected helical (TPH) edge states when the AB and BA regions are gapped. We fabricate designer moir{\'e} crystals with wavelengths longer than 50 nm and demonstrate the emergence of TPH states on the domain wall network by scanning tunneling spectroscopy measurements. We observe a double-line profile of the TPH states on the domain walls, only occurring when the AB and BA regions are gapped. Our results demonstrate a practical and flexible method for TPH state network construction.