Abstract :
Summary form only given, as follows. The recent focus of research in graphitic materials, such as fullerenes and carbon nanotubes has renewed interest in electronic transport in graphene, a single atomic layer of graphite. While graphite is a semimetal with strong electron and hole compensation, graphene is expected to be a zero-gap semiconductor with a vanishing density of states at the charge neutral point. Electrical transport in thin graphite crystals composed of only a few graphene layers is of particular interest in elucidating the evolution of electronic structure from bulk single crystals to two-dimensional planar systems. In this talk, we present results from the electric field effect dependent magnetoresistance and Hall resistance measurements in mesoscopic graphite crystallites consisting of as few as tens of atomic layers and also the measurements in graphene, a single sheet limit of graphite. The mesoscopic graphite devices used in this experiment are fabricated using a unique micro-mechanical method. Strong modulation of magneto-resistance and Hall resistance as a function of gate voltage is observed as sample thickness approaches the screening length. The electric-field effect changes the sign of the dominant majority carrier, hence reverses the sign of the Hall coefficient. Electric field dependent Landau level formation is detected from Shubnikov de Haas oscillations in the magneto-resistance. The effective mass of electron and hole carriers has been measured from the temperature dependent behavior of these oscillations.
