Transport in metallic multi-island Coulomb blockade systems: A systematic perturbative expansion in the junction transparency

TL;DR

This paper presents a systematic perturbative method to analyze electronic transport in multi-island Coulomb blockade systems, accounting for various tunneling processes and energy renormalizations, with applications to coupled island configurations.

Contribution

Develops a comprehensive diagrammatic real-time algorithm for second-order transport calculations in multi-island systems, including cotunneling and energy renormalization effects.

Findings

Multi-island cotunneling processes are significant in Coulomb blockade regimes.

Photon-assisted tunneling explains current in coupled island systems.

Comparison with P(E)-theory validates the approach in weak coupling limit.

Abstract

We study electronic transport through metallic multi-island Coulomb-blockade systems. Based on a diagrammatic real-time approach, we develop a computer algorithm that generates and calculates all transport contributions up to second order in the tunnel-coupling strengths for arbitrary multi-island systems. This comprises sequential and cotunneling, as well as terms corresponding to a renormalization of charging energies and tunneling conductances. Multi-island cotunneling processes with energy transfer between different island are taken into account. To illustrate our approach we analyze the current through an island in Coulomb blockade, that is electrostatically coupled to a second island through which a large current is flowing. In this regime both cotunneling processes involving one island only as well as multi-island processes are important. The latter can be understood as photon-assisted sequential tunneling in the blockaded island, where the photons are provided by potential fluctuations due to sequential tunneling in the second island. We compare results of our approach to a P(E)-theory for photon-assisted tunneling in the weak coupling limit.