Interplay of charge and spin dynamics after an interaction quench in the Hubbard model

We investigate the unitary dynamics following a sudden increase Delta U > 0 of repulsion in the paramagnetic sector of the half-filled Hubbard model on a Bethe lattice, by means of a variational approach that combines a Gutzwiller wave function with a partial Schrieffer-Wolff transformation, both defined through time-dependent variational parameters. Besides recovering at Delta U-c the known dynamical transition linked to the equilibrium Mott transition, we find a pronounced dynamical anomaly at larger Delta U-* > Delta U-c manifested in a singular behavior of the long-time average of double occupancy. Although the real-time dynamics of the variational parameters at Delta U-* strongly resembles the one at Delta U-c, a careful frequency spectrum analysis suggests a dynamical crossover, instead of a dynamical transition, separating regions of a different behavior of the spin exchange

Electron transport through strongly interacting quantum dot coupled to normal metal and superconductor

We study the electron transport through the quantum dot coupled to the normal metal and BCS-like superconductor (N - QD - S) in the presence of the Kondo effect and Andreev scattering. The system is described by the single impurity Anderson model in the limit of strong on-dot interaction. We use recently proposed equation of motion technique for Keldysh nonequilibrium Green's function together with the modified slave boson approach to study the electron transport. We derive formula for the current which contains various tunneling processes and apply it to study the transport through the system. We find that the Andreev conductance is strongly suppressed and there is no zero-bias (Kondo) anomaly in the differential conductance. We discuss effects of the particle-hole asymmetry in the electrodes as well as the asymmetry in the couplings.Comment: Supercond. Sci. Technol. - accepted for publicatio