Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 34: Correlated Electrons - Quantum Impurities, Kondo Physics

TT 34.2: Vortrag

Mittwoch, 9. März 2005, 10:00–10:15, TU H104

Non-equilibrium Transport and Approximate Conductance Quantization in Multi-level Quantum Dot Systems — •S. Kirchner¹, J. Kroha², and P. Wölfle³ — ¹Rice University — ²Universität Bonn — ³Universität Karlsruhe

Nanoconstrictions or quantum dots with several local levels or channels contributing to the conductance are prototypical systems for numerous quantum point contact devices, markedly for transport through single atoms, molecules or carbon nanotubes, many of them showing the tendency to conductance quantization. We discuss that for several local levels the lead-dot coupling matrix Γ _nm is, by principle, not left-right symmetric. As a consequence, within a generalized Landauer-Büttiker approach the conductance is determined by both, the local density of states and the local distribution functions, even in the linear response regime, thus drawing the connection to the Kubo formula. We consider the case of strong Coulomb correlations U≫ |Γ _nm| within the quantum point contact. While for a single transmission channel the Friedel sum rule strictly enforces quantization of the zero-temperature linear conductance, we show that for several levels there are systematical deviations due to the appearance of multiple Kondo-like resonances near the Fermi level. For the case of two transmission channels, relevant for carbon nanotubes, we give an analytical conductance formula and present results of numerical calculations for the general case both in and out of equilibrium.