Nonequilibrium transport through a quantum dot coupled to normal and superconducting leads

We study the interacting quantum dot coupled to the normal and superconducting leads by means of a continuous-time quantum Monte Carlo method in the Keldysh-Nambu formalism. Deducing the steady current through the quantum dot under a finite voltage, we examine how the gap magnitude in the superconducting lead and the interaction strength at the quantum dot affect transport properties. It is clarified that the Andreev reflection and Kondo effect lead to nonmonotonic behavior in the nonequilibrium transport at zero temperature.Comment: 6 pages, 3 figures, conference paper of SCES 201

Systematic Analysis of Frustration Effects in Anisotropic Checkerboard Lattice Hubbard Model

We study the ground state properties of the geometrically frustrated Hubbard model on the anisotropic checkerboard lattice with nearest-neighbor hopping $t$ and next nearest-neighbor hopping $t'$. By using the path-integral renormalization group method, we study the phase diagram in the parameter space of the Hubbard interaction $U$ and the frustration-control parameter $t'/t$. Close examinations of the effective hopping, the double occupancy, the momentum distribution and the spin/charge correlation functions allow us to determine the phase diagram at zero temperature, where the plaquette-singlet insulator emerges besides the antiferromagnetic insulator and the paramagnetic metal. Spin-liquid insulating states without any kind of symmetry breaking cannot be found in our frustrated model.Comment: 7pages, 5figure

Commutation relations of vertex operators related with the spin representation of Uq(Dn(1))U_q(D_n^{(1)})

We calculate commutation relations of vertex operators for the spin representation of $U_q(D_n^{(1)})$ by using recursive formulae of R-matrices. In quantum symmetry approach, we obtain the energy and momentum spectrum of the quantum spin chain model related with the spin representation from these commutation relations.Comment: 39 pages amslate