Strong Tunneling in Double-Island Structures

TL;DR

This paper investigates how coherent tunneling influences electron transport in double-island metallic systems, revealing peak broadening, shifts, and asymmetries in conductance, with implications for understanding phase transitions in coupled quantum dots.

Contribution

It applies a renormalization group approach to analyze high conductance tunneling in double-island systems, extending understanding of coherent effects beyond semiconducting double-dots.

Findings

Conductance peaks are reduced and broadened asymmetrically.

Peak positions shift depending on coupling strength.

Results align with theoretical predictions of phase transition behavior.

Abstract

We study the electron transport through a system of two low-capacitance metal islands connected in series between two electrodes. The work is motivated in part by experiments on semiconducting double-dots, which show intriguing effects arising from coherent tunneling of electrons and mixing of the single-electron states across tunneling barriers. In this article, we show how coherent tunneling affects metallic systems and leads to a mixing of the macroscopic charge states across the barriers. We apply a recently formulated RG approach to examine the linear response of the system with high tunnel conductances (up to 8e^2/h). In addition we calculate the (second order) cotunneling contributions to the non-linear conductance. Our main results are that the peaks in the linear and nonlinear conductance as a function of the gate voltage are reduced and broadened in an asymmetric way, as well as shifted in their positions. In the limit where the two islands are coupled weakly to the electrodes, we compare to theoretical results obtained by Golden and Halperin and Matveev et al. In the opposite case when the two islands are coupled more strongly to the leads than to each other, the peaks are found to shift, in qualitative agreement with the recent prediction of Andrei et al. for a similar double-dot system which exhibits a phase transition.