Observation of the underscreened Kondo effect in a molecular transistor

TL;DR

This paper provides the first experimental evidence of the underscreened Kondo effect in a molecular transistor, demonstrating its unique conductance behavior and magnetic field sensitivity through precise measurements and numerical analysis.

Contribution

It reports the first quantitative experimental observation of the underscreened Kondo effect in a molecular quantum dot with S=1, highlighting its distinct conductance features and magnetic response.

Findings

Logarithmic singularities in low-temperature conductance

Sensitivity of the Kondo resonance to magnetic fields

Comparison with fully screened S=1/2 Kondo configuration

Abstract

We present the first quantitative experimental evidence for the underscreened Kondo effect, an uncomplete compensation of a quantized magnetic moment by conduction electrons, as originally proposed by Nozieres and Blandin. The device consists of an even charge spin S = 1 molecular quantum dot, obtained by electromigration of C60 molecules into gold nanogaps and operated in a dilution fridge. The persistence of logarithmic singularities in the low temperature conductance is demonstrated by a comparison to the fully screened configuration obtained in odd charge spin S = 1/2 Coulomb diamonds. We also discover an extreme sensitivity of the underscreened Kondo resonance to magnetic field, that we confirm on the basis of numerical renormalization group calculations.