Nonequilibrium Quantum Impurity Systems

The Kondo effect plays an important role in the field of mesoscopics. At low energies spin-flip scatterings become more probable and that has a large effect on the conduction and the other macroscopic properties of the system. Quantum dots are devices that allow us to tune various parameters to achieve different kinds of Kondo systems such as the single channel and two-channel Kondo systems that have qualitatively different ground states. Experimentally it is also possible to drive these systems out of equilibrium.;In Chapter (2) we study the infinite-U Anderson model which has been driven out of the equilibrium by applying different chemical potentials to the leads so that there is current flow. We use a large-N approach to compute the voltage dependent conductance and the voltage dependent magnetic susceptibility where N is the number of the spin components.;In Chapter (3) we study a system where a local spin is connected to two independent reservoirs and a rapid change of gate voltages brings the system from the one-channel to the two-channel Kondo regime. The time evolution of the magnetization and the spin susceptibility are computed for the case when magnetic field couples to the local spin only and for the case where the magnetic field couples to the total spin (conduction electrons plus local spin).