Transport signatures of Van Hove singularities in mesoscopic twisted bilayer graphene

TL;DR

This paper investigates how Van Hove singularities influence transport properties in mesoscopic twisted bilayer graphene, revealing their role in conductance features and potential for high-frequency device applications.

Contribution

It establishes a direct link between conductance features and Van Hove singularities, highlighting their impact on transport phenomena in small-angle twisted bilayer graphene.

Findings

Conductance features correlate with Van Hove singularities.

Pressure-tunable minimal conductance observed.

Large conductance oscillations as a function of system size.

Abstract

Magic-angle twisted bilayer graphene exhibits quasi-flat low-energy bands with Van Hove singularities close to the Fermi level. These singularities play an important role in the exotic phenomena observed in this material, such as superconductivity and magnetism, by amplifying electronic correlation effects. In this work, we study the correspondence of four-terminal conductance and the Fermi surface topology as a function of the twist angle, pressure, and energy in mesoscopic, ballistic samples of small-angle twisted bilayer graphene. We establish a correspondence between features in the wide-junction conductance and the presence of van Hove singularities in the density of states. Moreover, we identify additional transport features, such as a large, pressure-tunable minimal conductance, conductance peaks coinciding with non-singular band crossings, and unusually large conductance oscillations as a function of the system size. Our results suggest that twisted bilayer graphene close the magic angle is a unique system featuring simultaneously large conductance due to the quasi-flat bands, strong quantum nonlinearity due to the Van Hove singularities and high sensitivity to external parameters, which could be utilized in high-frequency device applications and sensitive detectors.