Tunable spin/charge Kondo effect at a double superconducting island connected to two spinless quantum wires

TL;DR

This paper proposes a tunable double superconducting island system that can switch between spin and charge Kondo effects, with potential for experimental detection via conductance measurements.

Contribution

It introduces a novel engineered system enabling control over spin and charge Kondo phases through a single gate voltage, highlighting a new way to study the elusive charge-2 Kondo effect.

Findings

System can switch between spin and charge Kondo phases

Identification of an intermediate phase where the impurity is irrelevant

Proposed conductance measurements to detect charge-2 Kondo effect

Abstract

We propose that a pertinently engineered double superconducting island connected to two spinless one-dimensional conducting leads can work as a tunable (iso)spin Kondo and charge Kondo system, with the lead index regarded as an effective isospin degree of freedom. We evidence how, by tuning a single gate voltage applied to the island, it is possible to make the system switch from the (iso)spin Kondo to the charge-Kondo phase, passing across an intermediate phase, in which the Kondo impurity is effectively irrelevant for the low-temperature behavior of the system. Eventually, we evidence how to probe the various phases by measuring the ac conductance tensor of our system, by emphasizing the features that should allow to identify the onset of the so far quite elusive "charge-2" charge-Kondo effect.