Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 64: Superconductivity: Heterostructures, Andreev Scattering, Vortex Physics

TT 64.6: Talk

Thursday, March 14, 2013, 16:15–16:30, H21

Josephson current through a quantum dot coupled to a molecular magnet — •Pascal Stadler, Cecilia Holmqvist, and Wolfgang Belzig — Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany

Non-dissipative Josephson currents are carried by sharp Andreev states within the superconducting energy gap. We theoretically study the electronic transport of a magnetically tunable nanoscale junction consisting of a quantum dot connected to two superconducting leads and coupled to the spin of a molecular magnet. The exchange interaction between the molecular magnet and the quantum dot modifies the Andreev states due to a spin-dependent renormalization of the quantum dot’s energy level and the induction of spin-flips. A magnetic field applied to the central region of the quantum dot and the molecular magnet further tunes the Josephson current and starts a precession of the molecular magnet’s spin. We use a non-equilibrium Green’s function approach to evaluate the transport properties of the junction. Our calculations reveal that the magnetic field and the exchange interaction between the molecular magnet and the electrons occupying the energy level of the quantum dot can trigger transitions from a 0 to a π state of the Josephson junction. The redistribution of the occupied state induced by the magnetic field strongly modifies the current phase relation. The critical current exhibits a sharp increase as a function of the magnetic field.