quasiparticle interference imaging*

The existence of strong trigonal warping around the K point for the low energy electronic states in multilayer 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 resolve this disagreement. We compare Fourier transforms of scattering interference maps acquired at various energies away from the charge neutrality point with joint density of states simulations. This comparison permits unambiguous determination of the trigonal warping orientation for bilayer graphene at low energy. Our experimental technique is promising for studying quasi-directly fine features of the band structure of two-dimensional materials such as band topologies and Lifshitz transitions.