Nonlinear Response of a Kondo system: Direct and Alternating Tunneling Currents

TL;DR

This paper investigates the nonlinear tunneling currents in a Kondo system under both constant and alternating electric fields, revealing how ac fields suppress zero-bias anomalies and enhance certain harmonic responses.

Contribution

It introduces a time-dependent Schrieffer-Wolff transformation and derives a simple analytical expression for tunneling current in a Kondo system under non-equilibrium conditions.

Findings

Zero-bias anomaly is suppressed by an ac field.

Both dc and first harmonic currents are enhanced by the Kondo effect.

Higher harmonics are relatively small and the results hold below the Kondo temperature.

Abstract

Non - equilibrium tunneling current of an Anderson impurity system subject to both constant and alternating electric fields is studied. A time - dependent Schrieffer - Wolff transformation maps the time - dependent Anderson Hamiltonian onto a Kondo one. Perturbation expansion in powers of the Kondo coupling strength is carried out up to third order, yielding a remarkably simple analytical expression for the tunneling current. It is found that the zero - bias anomaly is suppressed by an ac - field. Both dc and the first harmonic are equally enhanced by the Kondo effect, while the higher harmonics are relatively small. These results are shown to be valid also below the Kondo temperature.