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

The existence of strong trigonal warping around the K point for the low-energy electronic states in multilayer (N >= 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 quasidirectly studying fine features of the band structure of gated two-dimensional materials such as topological transitions, interlayer hybridization, and moire minibands.