Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 2: Transport: Nanoelectronics I - Quantum Dots and Wires, Point Contacts 1

TT 2.7: Vortrag

Montag, 23. März 2009, 12:00–12:15, HSZ 301

Application of the weak-coupling CTQMC method to a Quantum Dot coupled to superconducting leads — •David J. Luitz and Fakher F. Assaad — Institut für Theoretische Physik und Astrophysik, Universität Würzburg, D-97074 Würzburg, Germany

We apply the weak-coupling continuous time quantum Monte Carlo (CTQMC) method to the Anderson-model extended by a BCS term to describe a quantum dot coupled to s-wave superconducting leads. As the superconducting gap Δ grows, our data shows a phase transition from the 0- to π-junction regime of the Josephson current. By examining various spectral functions, we confirm the traditional interpretation that the Kondo-effect at small Δ corresponds to the 0-junction-regime, while the formation of a magnetic moment on the quantum dot leads to the π-phase-shift at large Δ. At constant Δ, the double occupancy as a function of U shows a jump, thereby signaling a first order transition between the singlet and local moment doublet regimes.

Within DMFT, this impurity problem provides a link to the periodic Anderson model (PAM) with superconducting conduction electrons. The signature of this first order transition in the impurity model in the PAM will be discussed.