Regensburg 2010 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 29: TR: Nanoelectronics I: Quantum Dots, Wires, Point Contacts 1
TT 29.5: Talk
Thursday, March 25, 2010, 10:30–10:45, H19
Non-equilibrium transport through a two-level quantum dot: a renormalization-group analysis — •Sarah Müller1, Sabine Andergassen1, Verena Koerting2, and Dirk Schuricht1 — 1Institut für Theoretische Physik A und JARA - Fundamentals of Future Information Nanotechnology, RWTH Aachen University — 2Niels Bohr Institute, Universitetsparken 5, 2100 København Ø, Denmark
Transport through quantum dots is in general characterized by asymmetric couplings to the leads. In particular, in molecules and nanowires the coupling of each individual orbital level can be different. Motivated by recent experiments, we therefore study the effects of asymmetric hopping parameters on the non-equilibrium current and occupation probabilities of a two-level quantum dot. Starting from a two-level Anderson model, we perform a generalized Schrieffer-Wolff transformation to derive an effective Kondo model. A first perturbative analysis of the cotunneling current allows to determine a regime of negative differential conductance arising for couplings being both asymmetric with respect to the leads as well as to the quantum dot levels. Due to the non-equilibrium occupation of the levels inelastic cotunneling transitions are allowed not only from the ground state but from the excited state. The dependence of this cascade resonance on the magnetic field is discussed in detail. Since we expect the cotunneling lines to be measured experimentally for strong values of the couplings, we study the logarithmic enhancement of the ascribed signatures by means of a poor-man's renormalization-group treatment out of equilibrium.