Regensburg 2002 – scientific programme
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SYQT: Quantentransport auf molekularen Skalen
SYQT 2: Quantentransport auf molekularen Skalen
SYQT 2.1: Invited Talk
Monday, March 11, 2002, 14:30–15:00, H2
Electronic transport through atomic-size contacts — •E. Scheer, C. Bacca, C. Debuschewitz, J. Grebing, R. Hackl, V. Kunej, H.-F. Pernau, C. Schirm, and U. Schröter — Fachbereich Physik, Universität Konstanz, 78457 Konstanz
With the help of mechanically controllable breakjunctions (MCB) we have produced ultra-stable adjustable atomic-size contacts between two metallic banks. Since the Fermi wavelength in metals is of the order of the inter-atomic distance, a fully quantum mechanical description is required, treating the transport as a wave scattering problem. Within this approach the contacts represent electronic waveguides which accommodate only a small number of so-called "conduction channels". The number N and the individual transmission coefficients 0 < τi ≤ 1 of these channels represent the "genetic code" of a particular contact from which many other transport properties as e.g. thermopower, shot noise or supercurrent can be calculated.
The set { τi } can be revealed when using superconducting metals since their current-voltage characteristics display strong nonlinearities - called subgap structure - associated with multiple Andreev reflection. By this method we have determined the number of conduction channels and the individual transmission coefficients of contacts of elements covering several series of the periodic table. We find that N and { τi } of single-atom contacts depend strongly on the chemical nature of the central atom of the contact and its local environment. We show how the procedure can be extended to normal-conducting and magnetic metals. First results on semimetals and semiconductor clusters will be presented.