Signatures of quantum phase transitions in parallel quantum dots: Crossover from local-moment to underscreened spin-1 Kondo physics

TL;DR

This paper investigates quantum phase transitions in parallel quantum dots, revealing how varying interactions lead to different Kondo regimes and how these transitions can be detected via conductance measurements.

Contribution

It provides a detailed analysis of the crossover from local-moment to underscreened spin-1 Kondo physics in coupled quantum dots, highlighting signatures of quantum phase transitions.

Findings

Identification of Kosterlitz-Thouless quantum phase transitions.

Evolution of the free moment from spin-1/2 to a many-body doublet.

Distinct conductance signatures for different spin correlations.

Abstract

We study a strongly interacting "quantum dot 1" and a weakly interacting "dot 2" connected in parallel to metallic leads. Gate voltages can drive the system between Kondo-quenched and non-Kondo free-moment phases separated by Kosterlitz-Thouless quantum phase transitions. Away from the immediate vicinity of the quantum phase transitions, the physical properties retain signatures of first-order transitions found previously to arise when dot 2 is strictly noninteracting. As interactions in dot 2 become stronger relative to the dot-lead coupling, the free moment in the non-Kondo phase evolves smoothly from an isolated spin-one-half in dot 1 to a many-body doublet arising from the incomplete Kondo compensation by the leads of a combined dot spin-one. These limits, which feature very different spin correlations between dot and lead electrons, can be distinguished by weak-bias conductance measurements performed at finite temperatures.