Dynamical Coulomb blockade of tunnel junctions driven by alternating voltages

TL;DR

This paper extends dynamical Coulomb blockade theory to include tunnel junctions driven by time-dependent voltages, revealing how electromagnetic environment modes are excited and affect current harmonics.

Contribution

It introduces a unitary transformation approach to simplify calculations for ac-driven tunneling, connecting standard theory with new effects caused by alternating voltages.

Findings

Electromagnetic environment modes are excited by ac voltages.

Higher current harmonics are suppressed by the environment.

The theory applies broadly to all ac-driven tunneling devices.

Abstract

The theory of dynamical Coulomb blockade is extended to tunneling elements driven by a time-dependent voltage. It is shown that for standard set-ups where an external voltage is applied to a tunnel junction via an impedance, time-dependent driving entails an excitation of the modes of the electromagnetic environment by the applied voltage. Previous approaches for ac driven circuits need to be extended to account for the driven bath modes. A unitary transformation involving also the variables of the electromagnetic environment is introduced which allows to split-off the time-dependence from the Hamiltonian in the absence of tunneling. This greatly simplifies perturbation-theoretical calculations based on treating the tunneling Hamiltonian as a perturbation. In particular, the average current flowing in the leads of the tunnel junction is studied. Explicit results are given for the case of an applied voltage with a constant dc part and a sinusoidal ac part. The connection with standard dynamical Coulomb blockade theory for constant applied voltage is established. It is shown that an alternating voltage source reveals significant additional effects caused by the electromagnetic environment. The hallmark of dynamical Coulomb blockade in ac driven devices is a suppression of higher harmonics of the current by the electromagnetic environment. The theory presented basically applies to all tunneling devices driven by alternating voltages.