Regensburg 2013 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 4: Transport: Quantum Dots, Wires, Point Contacts 1 (jointly with HL and TT)

O 4.8: Vortrag

Montag, 11. März 2013, 11:30–11:45, H20

Nonlinear transport through interacting quantum dots with superconducting leads in the weak coupling regime — •Sascha Ratz and Milena Grifoni — Institut für Theoretische Physik, Universität Regensburg, 93040 Regensburg, Germany

We present a nonequilibrium real-time diagrammatic transport theory for the systematic investigation of the quasiparticle and Josephson currents through a hybrid superconductor-quantum dot system in the weak coupling regime. In details, our device consists of an interacting quantum dot coupled to two biased spin-singlet superconducting leads. To describe the transport dynamics, we derive a completely general equation of motion for the reduced density matrix including all the contributions of a perturbation expansion in the tunneling Hamiltonian. Within these investigations, already in fourth order we can identify the contributions of the nonlocal time evolution kernel to the quasiparticle and DC Josephson transport. To clarify the difference between quasiparticle cotunneling and phase-coherent two-particle Andreev tunneling in fourth order, we first choose a single-level Anderson impurity model for the interacting quantum dot. In particular, one can give a clear explanation for subgap features due to proximity effects, which are also important when we finally compare our theoretical results for a carbon nanotube quantum dot with experimental observations.