Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 27: Symposium “Graphene”

TT 27.4: Hauptvortrag

Donnerstag, 29. März 2007, 15:20–15:50, H20

Transport properties of mesoscopic graphene — •Björn Trauzettel — Department of Physics and Astronomy, University of Basel, CH-4056 Basel, Switzerland

Two recent experiments have discovered that the conductivity of graphene (a single atomic layer of carbon) tends to a minimum value of the order of the quantum unit e²/h when the concentration of charge carriers tends to zero. This quantum-limited conductivity is an intrinsic property of two-dimensional Dirac fermions (massless excitations governed by a relativistic wave equation), which persists in an ideal crystal without any impurities. In the absence of impurity scattering, and at zero temperature, one might expect the electrical current to be noiseless. In contrast, we show that the minimum in the conductivity is associated with a maximum in the Fano factor (the ratio of noise power and mean current). The Fano factor at zero carrier concentration takes on the universal value 1/3 for a wide and short graphene strip. This is three times smaller than the Poissonian noise in a tunnel junction and identical to the value in a disordered metal. We discuss the relation of this result to the phenomenon of zitterbewegung which is present for free Dirac fermions but absent for free Schrödinger fermions.

Work done in collaboration with C.W.J. Beenakker, Ya.M. Blanter, A.F. Morpurgo, A. Rycerz, M. Titov, and J. Tworzydlo.