Observation of Van Hove singularities in twisted graphene layers

TL;DR

This paper reports the experimental observation of tunable Van Hove singularities in twisted graphene layers, achieved by rotating the layers to bring these singularities close to the Fermi energy, enabling potential electronic phase engineering.

Contribution

It demonstrates that twisting graphene layers can generate and control Van Hove singularities near the Fermi energy, a novel method for electronic phase manipulation.

Findings

Van Hove singularities observed as peaks in density of states

Rotation angle controls the energy position of singularities

Potential for engineering electronic phases in graphene

Abstract

Electronic instabilities at the crossing of the Fermi energy with a Van Hove singularity in the density of states often lead to new phases of matter such as superconductivity, magnetism or density waves. However, in most materials this condition is difficult to control. In the case of single-layer graphene, the singularity is too far from the Fermi energy and hence difficult to reach with standard doping and gating techniques. Here we report the observation of low-energy Van Hove singularities in twisted graphene layers seen as two pronounced peaks in the density of states measured by scanning tunneling spectroscopy. We demonstrate that a rotation between stacked graphene layers can generate Van Hove singularities, which can be brought arbitrarily close to the Fermi energy by varying the angle of rotation. This opens intriguing prospects for Van Hove singularity engineering of electronic phases.