1/N expansion of the nonequilibrium infinite-U Anderson Model

TL;DR

This paper investigates the nonequilibrium infinite-U Anderson model using a large-N approach, revealing how current flow affects physical observables and their asymmetries in the Kondo and mixed valence regimes.

Contribution

It provides the first ${ m O}(1/N)$ analytical expressions for spin susceptibility and conductance under nonequilibrium conditions, highlighting the impact of current-induced decoherence.

Findings

Slave-boson correlation functions decay rapidly out of equilibrium

Physical observables show asymmetry with respect to voltage reversal

Current flow induces decoherence affecting the impurity dynamics

Abstract

Results are presented for the nonequilibrium infinite-U Anderson model using a large-N approach, where $N$ is the degeneracy of the impurity level, and where nonequilibrium is established by coupling the level to two leads at two different chemical potentials so that there is current flow. A slave-boson representation combined with Keldysh functional integral methods is employed. Expressions for the static spin susceptibility $\chi_S$ and the conductance $G$ are presented to ${\cal O}(\frac{1}{N})$ and for an applied voltage difference $V$ less than the Kondo temperature. The correlation function for the slave-boson is found to be significantly modified from its equilibrium form in that it acquires a rapid decay in time with a rate that equals the current induced decoherence rate. Physical observables are found to have a rather complex dependence on the coupling strength to the two leads which can lead to asymmetric behavior $\chi_S(V) \neq \chi_S(-V)$, $G(V)\neq G(-V)$ both in the mixed valence and in the Kondo regime.