Browsing by Author "Valles, JM"

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Negative magnetoresistance, negative electroresistance, and metallic behavior on the insulating side of the two-dimensional superconductor-insulator transition in granular Pb films
(2006-04-01)
Barber, RP
;
Hsu, SY
;
Valles, JM
;
Dynes, RC
;
Glover, RE
Granular Pb thin films on the insulating side of the two-dimensional superconductor-insulator transition are observed to exhibit a large negative magnetoresistance and electroresistance (change in resistance with electric field) at low temperatures. At high measurement voltages and low temperatures, the film resistances become temperature independent creating a "metallic" state. These phenomena are explained as manifestations of transport due to intergranular quasiparticle tunneling. This explanation might also provide insights into the similar behavior observed in other superconductors.
Tunneling measurements of fluctuation effects near the superconductor to insulator transition
(1998-10-01)
Hsu, SY
;
Chervenak, JA
;
Valles, JM
;
電子物理學系
;
Department of Electrophysics
We present measurements of the temperature dependence of the tunneling density of states near the Fermi energy, G(o)(T), and resistive transitions, R(T), of ultrathin PbBi films. Both R(T) and G(o)(T) broaden substantially near the superconductor to insulator transition (SIT). The broadening in R(TI is not affected by the proximity of a ground plane suggesting that long range Coulomb interactions are not important to the SIT. The results suggest that the transport properties of Alms near the SIT are influenced by fluctuations in both the phase and the amplitude of the order parameter. We discuss the data in terms of recent theories of the superconducting transition in low superfluid density systems. (C) 1998 Elsevier Science Ltd. All rights reserved.