Berlin 2008 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 22: Transport: Poster Session

TT 22.30: Poster

Mittwoch, 27. Februar 2008, 14:00–18:00, Poster B

Point contact spectroscopy of quench-condensed Ag films — •Torben Peichl, Marcel Spurny, Michael Burst, and Georg Weiß — Physikalisches Institut, Universität Karlsruhe, 76128 Karlsruhe, Germany

We report on the progress in fabricating nanostructured point contacts as a result of our structural characterization studies. The point contacts are defined by electron beam lithography on top of silicon nitride membranes. Then the bottom side is covered with a layer of Au before a SF₆ plasma etching from the top side is used to obtain nano-sized holes in the membrane. Finally, a highly disordered Ag layer is prepared by quench-condensing Ag films at low temperatures <10 K on the top side. This results in metallic point contacts with diameters <50 nm and resistances between 1 and 10 Ω.

Electronic transport properties of these point contacts were studied at temperatures from 1.5 to 8 K by measuring the differential resistance using lock-in methods. Within sample series we find reproducible results, in particular a distinct minimum of the differential resistance which we identify as a zero-bias minimum shifted by a DC offset of yet unknown origin. This minimum becomes narrower at increasing temperatures and vanishes at 8 K. Similarly, the minimum diminishes continuously with magnetic field until it vanishes completely at about 2 T. Low energy excitations as well as coulomb blockade effects might be responsible for the observed behavior. Additionally, slight osciallations of the differential resistance curves are reminiscent of weak localisation effects.