Electronic spectrum of twisted graphene layers under heterostrain

TL;DR

This paper explores how heterostrain, where layers are strained independently, significantly alters the electronic spectrum of twisted graphene layers, enabling new strain engineering possibilities in 2D materials.

Contribution

It introduces heterostrain as a novel strain engineering method and demonstrates its effects on the electronic properties of twisted graphene layers through experiments and calculations.

Findings

Heterostrain suppresses Dirac cones in TGLs.

Heterostrain induces flat bands in twisted graphene layers.

Heterostrain has a more severe impact on the energy spectrum than homostrain.

Abstract

We demonstrate that stacking layered materials allows a novel type of strain engineering where each layer is strained independently, which we call heterostrain. We combine detailed structural and spectroscopic measurements with tight-binding calculations to show that small uniaxial heterostrain suppresses Dirac cones and leads to the emergence of flat bands in twisted graphene layers (TGLs). Moreover, we demonstrate that heterostrain reconstructs much more severely the energy spectrum of TGLs than homostrain for which both layers are strained identically ; a result which should apply to virtually all van der Waals structure opening exciting possibilities for straintronics with 2D materials.