Akira Oguri

Spectral properties of locally correlated electrons in a Bardeen–Cooper–Schrieffer superconductor

We present a detailed study of the spectral properties of a locally correlated site embedded in a Bardeen–Cooper–Schrieffer (BCS) superconducting medium. To this end the Anderson impurity model with a superconducting bath is analysed by means of numerical renormalization group calculations. We calculate one-and two-particle dynamic response functions to elucidate the spectral excitations and the nature of the ground state for different parameter regimes with and without particle–hole symmetry. The position and weight of the Andreev bound states is given for all relevant parameters. We present phase diagrams for the different ground state parameter regimes. This work is also relevant for dynamical mean field theory extensions with superconducting symmetry breaking.

Numerical Renormalization Group Approach to a Quantum Dot Coupled to Normal and Superconducting Leads

We study transport through a quantum dot coupled to normal and superconducting leads using the numerical renormalization group method. We show that the low-energy properties of the system are described by the local Fermi liquid theory despite of the superconducting correlations penetrated into the dot due to a proximity effect. We calculate the linear conductance due to the Andreev reflection in the presence of the Coulomb interaction. It is demonstrated that the maximum structure appearing in the conductance clearly characterizes a crossover between two distinct spin-singlet ground states, i.e. the superconducting singlet state and the Kondo singlet state. It is further elucidated that the gate-voltage dependence of the conductance shows different behavior in the superconducting singlet region from that in the Kondo singlet region.

Fermi-liquid theory for the Anderson model out of equilibrium

The low-energy properties of the Anderson impurity are studied under a finite bias voltage V using the perturbation theory in U of Yamada and Yosida in the nonequilibrium Keldysh diagrammatic formalism. The self-energy is calculated exactly up to terms of order

Josephson current through a single Anderson impurity coupled to BCS leads

{\ensuremath{\omega}}^{2},

TRANSPORT THROUGH A FINITE HUBBARD CHAIN CONNECTED TO RESERVOIRS

{T}^{2},

Renormalized parameters for impurity models

and

Quasiparticle description for transport through a small interacting system

{V}^{2}

Quantum Phase Transition in a Minimal Model for the Kondo Effect in a Josephson Junction

using Ward identities. The coefficients are defined with respect to the equilibrium ground state, and contain all contributions of the perturbation series in U. From these results, the nonlinear response of the current through the impurity has been deduced up to order

Transmission Probability for Interacting Electrons Connected to Reservoirs

{V}^{3}.