The ability to create arbitrary stacking configurations of layered two-dimensional materials has opened the way to the creation of designer band structures. Twisted bilayer graphene and graphene on hexagonal boron nitride (hBN) are two of the simplest examples of such a van der Waals heterostructure where the electronic properties of the composite material can be fundamentally different from either individual material. These van der Waals heterostructures can be formed using a wide variety of layered materials including transition metal dichalcogenides, graphene and topological insulators. This talk will mostly focus on creating novel electronic states by controlling the twist angle and breaking inversion symmetry. The lattice mismatch and twist angle between layers in the heterostructure produces a moiré pattern which affects its electronic properties. For graphene on hBN, the moiré pattern creates a new set of superlattice Dirac points. In small twist angle bilayer graphene or transition metal dichalcogenides, the long-wavelength moiré pattern leads to the creation of flat bands and a wide range of correlated electronic states. In this talk, I will discuss our fabrication of these heterostructures and measurements using scanning probe microscopy.
BIO: Brian LeRoy is a professor and the director of graduate studies in the Physics department at the University of Arizona. He joined the UA faculty in 2006 after completing a post-doctoral research position at the Delft University of Technology working on scanning tunneling spectroscopy of carbon nanotubes. He received his PhD from Harvard University studying electron flow through semiconductor heterostructures. His current research interests are in the electrical and optical properties of low dimensional materials and van der Waals heterostructures. These measurements are performed using a combination of scanning probe microscopy and optical spectroscopy techniques. He has published extensively on the local electronic properties of van der Waals heterostructures including the first observations of moiré patterns in graphene/boron nitride heterostructures and the modification of the band structure. He is also an APS Fellow and the associate editor of the journal APL Materials.