Condensed Matter Physics Seminar

Graphene bilayers, a set of two closely spaced graphene monolayers, represent an interesting electron system, with potential device applications. We examine here the fabrication and electron transport in several graphene bilayer structures, which are either fabricated using a layer-by-layer transfer approach, or grown on SiC and Cu substrates. Independently contacted graphene double layers consist of two graphene layers in close proximity, separated by a thin dielectric. We discuss the fabrication of such samples, the electron transport in individual layers at zero and in a high magnetic field, and probe the inter-layer interaction via Coulomb drag measurements. We describe a novel technique which allows the measurement of the Fermi energy in one of the two layers, by using the opposite layer as a resistively detected Kelvin probe. A second bilayer system examined here consists of grown graphene bilayers with Bernal stacking. We discuss the fabrication of gated Hall bars on graphene bilayers grown on SiC and Cu substrates, and discuss the magneo-transport in these devices probed down to temperatures of 0.3 K and magnetic fields up to 30 T. The data reveals either quantum Hall states at filling factors  = 4, 8, 12, consistent with graphene bilayers in Bernal stacking, or the superposition of quantum Hall states of two independent monolayers, a finding consistent with a twisted graphene bilayer. We discuss potential device applications of graphene bilayers.