Quantum phase transition in a realistic double-quantum-dot system

TL;DR

This paper shows that in double-quantum-dot systems, tuning the energy difference between dots can induce a quantum phase transition, which is experimentally feasible and governed by Coulomb interactions.

Contribution

The study demonstrates a realistic method to induce quantum phase transitions in double-dot systems by tuning level energy differences, supported by numerical and semi-analytic analyses.

Findings

Energy difference tuning drives phase transition.

The transition is governed by Coulomb repulsion differences.

Mapping to an even-odd basis reveals the interaction competition.

Abstract

Observing quantum phase transitions in mesoscopic systems is a daunting task, thwarted by the difficulty of experimentally varying the magnetic interactions, the typical driving force behind these phase transitions. Here we demonstrate that in realistic coupled double-dot systems, the level energy difference between the two dots, which can be easily tuned experimentally, can drive the system through a phase transition, when its value crosses the difference between the intra- and inter-dot Coulomb repulsion. Using the numerical renormalization group and the semi-analytic slave-boson mean-field theory, we study the nature of this phase transition, and demonstrate, by mapping the Hamiltonian into an even-odd basis, that indeed the competition between the dot level energy difference and the difference in repulsion energies governs the sign and magnitude of the effective magnetic interaction. The observational consequences of this transition are discussed.