Kondo effect and spin-orbit coupling in graphene quantum dots

TL;DR

This paper reports the observation of both fully screened and underscreened Kondo effects in bilayer graphene quantum dots, providing a new platform to study complex Kondo phenomena with minimal spin-orbit coupling.

Contribution

It introduces bilayer graphene quantum dots as a novel platform for exploring diverse Kondo effects, including underscreened scenarios, with minimal spin-orbit interaction.

Findings

Observation of fully screened Kondo effect in bilayer graphene dots.

Detection of underscreened Kondo effect with spin-1 ground state.

Bilayer graphene offers a unique platform with low spin-orbit coupling.

Abstract

The Kondo effect is a cornerstone in the study of strongly correlated fermions. The coherent exchange coupling of conduction electrons to local magnetic moments gives rise to a Kondo cloud that screens the impurity spin. Whereas complete Kondo screening has been explored widely, realizations of the underscreened scenario - where only some of several Kondo channels participate in the screening - remain rare. Here we report the observation of fully screened and underscreened Kondo effects in quantum dots in bilayer graphene. More generally, we introduce a unique platform for studying Kondo physics. In contrast to carbon nanotubes, whose curved surfaces give rise to strong spin-orbit coupling breaking the SU(4) symmetry of the electronic states relevant for the Kondo effect, we study a nominally flat carbon material with small spin-orbit coupling. Moreover, the unusual two-electron triplet ground state in bilayer graphene dots provides a route to exploring the underscreened spin-1 Kondo effect.