Argonne National Laboratory

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Hopping Transport in Arrays of Metallic and Superconducting Grains

Materials Science Seminar
Brian Skinner, University of Minnesota
October 9, 2012 11:00AM to 12:00PM
Building 223, Room S105
Granular metals and granular superconductors are interesting composite systems, in which the unique properties of quantum dots are combined with collective, correlation-driven effects between grains to produce novel material properties. This interplay is particularly evident in the conductivity, which in the heavily insulating limit proceeds by hopping of electrons between isolated grains. In this talk I discuss a model of hopping conductivity in insulating arrays of metal or superconductor grains.

Using a simple computer simulation, we identify novel features of the single-particle density of states in these systems and calculate the conductivity as a function of temperature. For arrays of superconducting grains, we discuss the dependence of the conductivity on the strength of the superconducting gap, and identify an unusual \sqrt{2} effective charge that characterizes the hopping transport at a particular value of the gap. These results are discussed in light of recent experimental observations of a large magnetoresistance peak in certain granular superconductors.