Quantum phase transition and underscreened Kondo effect in electron transport through parallel double quantum dots

TL;DR

This paper studies electron transport in parallel double quantum dots with strong interactions, revealing a quantum phase transition and underscreened Kondo effect that influence conductance at low temperatures.

Contribution

It introduces a detailed analysis of the quantum phase transition and underscreened Kondo effect in double quantum dots using numerical renormalization group methods.

Findings

Ground state is a spin 1 triplet with ferromagnetic correlations.

Unitary conductance due to underscreened Kondo effect at low temperature.

Quantum phase transition suppresses conductance as interdot coupling increases.

Abstract

We investigate electronic transport through parallel double quantum dot(DQD) system with strong on-site Coulomb interaction and capacitive interdot coupling. By applying numerical renormalization group(NRG) method, the ground state of the system and the transmission probability at zero temperature have been obtained. For a system of quantum dots with degenerate energy levels and small interdot tunnel coupling, the spin correlations between the DQDs is ferromagnetic, and the ground state of the system is a spin 1 triplet state. The linear conductance will reach the unitary limit ($2e^2/h$) due to the underscreened Kondo effect at low temperature. As the interdot tunnel coupling increases, there is a quantum phase transition from ferromagnetic to anti-ferromagnetic spin correlation in DQDs and the linear conductance is strongly suppressed.