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TT: Fachverband Tiefe Temperaturen

TT 4: CE: Quantum Impurities, Kondo Physics

TT 4.3: Vortrag

Montag, 22. März 2010, 10:45–11:00, H21

A weak coupling CTQMC study of the single impurity and periodic Anderson models with s-wave superconducting baths — •David J. Luitz and Fakher F. Assaad — Institut für theoretische Physik und Astrophysik, Universität Würzburg, Deutschland

We apply the unbiased weak-coupling continuous time quantum Monte Carlo (CTQMC) method to review the physics of a single magnetic impurity coupled to s-wave superconducting leads described by the BCS reduced Hamiltonian. As a function of the superconducting gap Δ, we study the first order transition between the singlet and doublet (local moment) states by examining the crossing of the Andreev bound states in the single particle spectral function. Within DMFT, this impurity problem provides a link to the periodic Anderson model with superconducting conduction electrons (BCS-PAM). The first order transition observed in the impurity model is reproduced in the BCS-PAM and is signalized by the crossing of the low energy excitations in the local density of states. The momentum resolved single particle spectral function in the singlet state reveals the coherent, Bloch-like, superposition of Andreev bound states. In the doublet or local moment phase the single particle spectral function is characterized by incoherent quasiparticle excitations.