The Kondo Effect in Non-Equilibrium Quantum Dots: Perturbative Renormalization Group

TL;DR

This paper investigates the non-equilibrium Kondo effect in quantum dots under high bias voltage and magnetic field, using a generalized perturbative renormalization group approach to understand decoherence and transport properties.

Contribution

It introduces a generalized perturbative renormalization group method for non-equilibrium Kondo systems, accounting for energy-dependent couplings and decoherence effects.

Findings

Inelastic dephasing suppresses the Kondo effect at high bias.

Decoherence rate cuts off the RG flow within the perturbative regime.

Calculations of conductance, magnetization, and spectral functions are feasible for large V and B.

Abstract

While the properties of the Kondo model in equilibrium are very well understood, much less is known for Kondo systems out of equilibrium. We study the properties of a quantum dot in the Kondo regime, 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, we calculate renormalized couplings, keeping their important energy dependence. We show that in a magnetic field the spin occupation of the quantum dot is non-thermal, 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 (with possible exceptions). As a consequence, the differential conductance, the local magnetization, the spin relaxation rates and the local spectral function may be calculated for large V,B >> T_K in a controlled way.