Determination of the trigonal warping orientation in Bernal-stacked bilayer graphene via scanning tunneling microscopy

TL;DR

This study uses quasiparticle scattering experiments and simulations to determine the orientation of trigonal warping in bilayer graphene, clarifying a long-standing disagreement and demonstrating a method to explore detailed band structure features.

Contribution

It provides an unambiguous experimental method to determine the trigonal warping orientation in bilayer graphene using scattering interference maps and tight-binding simulations.

Findings

Unambiguous determination of trigonal warping orientation in bilayer graphene.

Validation of quasiparticle scattering as a tool for band structure analysis.

Potential to study fine electronic features in 2D materials.

Abstract

The existence of strong trigonal warping around the K point for the low energy electronic states in multilayer (N$\geq$2) graphene films and graphite is well established. It is responsible for phenomena such as Lifshitz transitions and anisotropic ballistic transport. The absolute orientation of the trigonal warping with respect to the center of the Brillouin zone is however not agreed upon. Here, we use quasiparticle scattering experiments on a gated bilayer graphene/hexagonal boron nitride heterostructure to settle this disagreement. We compare Fourier transforms of scattering interference maps acquired at various energies away from the charge neutrality point with tight-binding-based joint density of states simulations. This comparison enables unambiguous determination of the trigonal warping orientation for bilayer graphene low energy states. Our experimental technique is promising for quasi-directly studying fine features of the band structure of gated two-dimensional materials such as topological transitions, interlayer hybridization, and moir\'e minibands.