Nonequilibrium transport through quantum dots:
correlation effects.
Abstract:
While the properties of the Kondo model in
equilibrium are well understood, much less is known for Kondo systems out of
equilibrium. In this talk the
properties of a quantum dot in the Kondo regime will be discussed, specifically
when a large bias voltage V and/or a large magnetic field B is applied. Using the perturbative renormalization group
generalized to stationary nonequilibrium situations, the renormalized couplings
may be calculated, keeping their important energy dependence. We show that in a magnetic field the spin
occupation of the quantum dot is nonthermal, being controlled by V and B in a
complex way to be calculated by solving a quantum Boltzmann equation. We find that the well known suppression of
the Kondo effect at finite V >> T_K (Kondo temperature) is caused by
inelastic dephasing processes induced by the current through the dot. We calculate the corresponding decoherence
rate, which serves to cut off the RG flow usually well inside the perturbative
regime. As a consequence, the
differential conductance, the local magnetization, the spin relaxation rate and
the local spectral function may be calculated for V,B >> T_K in a
controlled way. Experimental data are
shown to be explained well by our theory.