Ballistic transport experiment detects Fermi surface anisotropy of graphene

TL;DR

This study demonstrates a ballistic transport method to detect Fermi surface anisotropy in graphene, revealing differences between monolayer and bilayer forms through magnetoresistance measurements.

Contribution

The paper introduces a novel ballistic transport technique to observe Fermi surface anisotropy in 2D materials, previously challenging to detect in transport experiments.

Findings

Fermi surface of bilayer graphene is trigonally warped.

Fermi surface of monolayer graphene is approximately circular.

Magnetoresistance depends on crystallographic orientation in bilayer graphene.

Abstract

Monolayer graphene and bilayer graphene have strikingly different properties. One such difference is the shape of the Fermi surface. Although anisotropic band structures can be detected in optical measurements, they have so far been difficult to detect in transport experiments on twodimensional materials. Here we describe a ballistic transport experiment using high-quality graphene that revealed Fermi surface anisotropy in the magnetoresistance. The shape of the Fermi surface is closely related with the cyclotron orbit in real space. Electron trajectories in samples with triangular lattices of holes depend on the anisotropy of the Fermi surface. We found that this results in the magnetoresistance which are dependent on crystallographic orientation of the antidot lattice, which indicates the anisotropic Fermi surface of bilayer graphene which is a trigonally-warped circle in shape. While in monolayer, shape of magnetoresistance was approximately independent of the orientation of antidot lattice, which indicates that the Fermi surface is a circle in shape. The ballistic transport experiment is a new method of detecting anisotropic electronic band structures in two-dimensional electron systems.