Twisted bilayer zigzag-graphene nanoribbon junctions with tunable edge states

TL;DR

This study demonstrates that the edge states in twisted bilayer zigzag graphene nanoribbons can be precisely tuned by adjusting the twist angle and stacking offset, revealing new possibilities for 1D twistronics.

Contribution

It introduces the concept of tunable edge states in twisted bilayer nanoribbons through combined twist angle and stacking offset control, supported by DFT and STM analyses.

Findings

Edge states are highly tunable by stacking offset.

Emergence of near-zero-energy states in junctions.

Formation of flat bands with adjustable energy and spin degeneracy.

Abstract

Stacking two-dimensional layered materials such as graphene and transitional metal dichalcogenides with nonzero interlayer twist angles has recently become attractive because of the emergence of novel physical properties. Stacking of one-dimensional nanomaterials offers the lateral stacking offset as an additional parameter for modulating the resulting material properties. Here, we report that the edge states of twisted bilayer zigzag graphene nanoribbons (TBZGNRs) can be tuned with both the twist angle and the stacking offset. Strong edge state variations in the stacking region are first revealed by density functional theory (DFT) calculations. We construct and characterize twisted bilayer zigzag graphene nanoribbon (TBZGNR) systems on a Au(111) surface using scanning tunneling microscopy. A detailed analysis of three prototypical orthogonal TBZGNR junctions exhibiting different stacking offsets by means of scanning tunneling spectroscopy reveals emergent near-zero-energy states. From a comparison with DFT calculations, we conclude that the emergent edge states originate from the formation of flat bands whose energy and spin degeneracy are highly tunable with the stacking offset. Our work highlights fundamental differences between 2D and 1D twistronics and spurs further investigation of twisted one-dimensional systems.