Unhiding a concealed resonance by multiple Kondo transitions in a quantum dot

TL;DR

This paper investigates how multiple Kondo transitions in a carbon nanotube quantum dot reveal hidden resonances, highlighting the role of asymmetries and pseudospin dynamics in Kondo transport phenomena.

Contribution

It uncovers the microscopic mechanisms behind the unhidden resonance in Kondo systems with SU(2)×SU(2) symmetry, emphasizing the impact of asymmetries and pseudospin transitions.

Findings

Resonant features at pseudospin-preserving transition bias observed.

Enhanced pseudospin-non-preserving transitions at the same bias.

Asymmetries in tunneling and potential drops facilitate the resonance.

Abstract

Kondo correlations are responsible for the emergence of a zero-bias peak in the low temperature differential conductance of Coulomb blockaded quantum dots. In the presence of a global SU(2)$\otimes$SU(2) symmetry, which can be realized in carbon nanotubes, they also inhibit inelastic transitions which preserve the Kramers pseudospins associated to the symmetry. We report on magnetotransport experiments on a Kondo correlated carbon nanotube where resonant features at the bias corresponding to the pseudospin-preserving transitions are observed. We attribute this effect to a simultaneous enhancement of pseudospin-non-preserving transitions occurring at that bias. This process is boosted by asymmetric tunneling couplings of the two Kramers doublets to the leads and by asymmetries in the potential drops at the leads. Hence, the present work discloses a fundamental microscopic mechanisms ruling transport in Kondo systems far from equilibrium.