Quantum phase transition in capacitively coupled double quantum dots

TL;DR

This paper explores a quantum phase transition in capacitively coupled double quantum dots, revealing a crossover from spin- to charge-Kondo physics, an intermediate SU(4) state, and a Kosterlitz-Thouless transition to a non-Fermi liquid phase.

Contribution

It uncovers a complex sequence of quantum states and a phase transition in coupled quantum dots using numerical and physical analysis.

Findings

Identification of spin- to charge-Kondo crossover

Discovery of an intermediate SU(4) entangled state

Observation of a Kosterlitz-Thouless transition to a non-Fermi liquid phase

Abstract

We investigate two equivalent, capacitively coupled semiconducting quantum dots, each coupled to its own lead, in a regime where there are two electrons on the double dot. With increasing interdot coupling a rich range of behavior is uncovered: first a crossover from spin- to charge-Kondo physics, via an intermediate SU(4) state with entangled spin and charge degrees of freedom; followed by a quantum phase transition of Kosterlitz-Thouless type to a non-Fermi liquid `charge-ordered' phase with finite residual entropy and anomalous transport properties. Physical arguments and numerical renormalization group methods are employed to obtain a detailed understanding of the problem.