pi-Junction behavior and Andreev bound states in Kondo quantum dots with superconducting leads

We investigate the temperature- and coupling-dependent transport through Kondo dot contacts with symmetric superconducting s-wave leads. For finite temperature T we use a superconducting extension of a selfconsistent auxiliary boson scheme, termed SNCA, while at T=0 a perturbative renormalization group treatment is applied. The finite-temperature phase diagram for the 0--pi transition of the Josephson current in the junction is established and related to the phase-dependent position of the subgap Kondo resonance with respect to the Fermi energy. The conductance of the contact is evaluated in the zero-bias limit. It approaches zero in the low-temperature regime, however, at finite T its characteristics are changed through the coupling- and temperature-dependent 0--pi transition.Comment: 12 pages, 12 figure

Nonequilibrium Transport through a Kondo Dot: Decoherence Effects

We investigate the effects of voltage induced spin-relaxation in a quantum dot in the Kondo regime. Using nonequilibrium perturbation theory, we determine the joint effect of self-energy and vertex corrections to the conduction electron T-matrix in the limit of transport voltage much larger than temperature. The logarithmic divergences, developing near the different chemical potentials of the leads, are found to be cut off by spin-relaxation rates, implying that the nonequilibrium Kondo-problem remains at weak coupling as long as voltage is much larger than the Kondo temperature.Comment: 16 pages, 4 figure

Diagrammatic theory of the Anderson impurity model with finite Coulomb interaction

We have developed a self-consistent conserving pseudo particle approximation for the Anderson impurity model with finite Coulomb interaction, derivable from a Luttinger Ward functional. It contains an infinite series of skeleton diagrams built out of fully renormalized Green's functions. The choice of diagrams is motivated by the Schrieffer Wolff transformation which shows that singly and doubly occupied states should appear in all bare diagrams symmetrically. Our numerical results for $T_K$ are in excellent agreement with the exact values known from the Bethe ansatz solution. The low energy physics of non-Fermi liquid Anderson impurity systems is correctly described while the present approximation fails to describe Fermi liquid systems, since some important coherent spin flip and charge transfer processes are not yet included. It is believed that CTMA (Conserving T-matrix approximation) diagrams will recover also Fermi liquid behavior for Anderson models with finite Coulomb interaction as they do for infinite Coulomb interaction.Comment: 4 pages, 2 figures, presented at the NATO Advanced Research Workshop on "Size Dependent MAgnetic Scattering", Pecs, Hungary, May 28 - June 1, 200

Vertex correction and Ward identity in the U(1) gauge theory with Fermi surface

We show that introduction of vertex corrections in the fully self-consistent ladder approximation does not modify dynamics of spinons and gauge fluctuations in the U(1) gauge theory with Fermi surface

Non Equilibrium Noise as a Probe of the Kondo Effect in Mesoscopic Wires

We study the non-equilibrium noise in mesoscopic diffusive wires hosting magnetic impurities. We find that the shot-noise to current ratio develops a peak at intermediate source-drain biases of the order of the Kondo temperature. The enhanced impurity contribution at intermediate biases is also manifested in the effective distribution. The predicted peak represents increased inelastic scattering rate at the non-equilibrium Kondo crossover.Comment: 4+ pages, 4 figures, published versio