Topologically Protected Helical States in Minimally Twisted Bilayer Graphene

Abstract

In minimally twisted bilayer graphene, a moiré 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 moiré 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.