Observation of the Underscreened Kondo Effect in a Molecular Transistor

Nicolas Roch (1) , Serge Florens (2) , Theo A. Costi (3) , Wolfgang Wernsdorfer (1) , Franck Balestro (1)

1 NEEL - QuantECA - Circuits électroniques quantiques Alpes
2 NEEL - ThQC - Théorie Quantique des Circuits
3 IKP - Institut für Kernphysik

We present the first quantitative experimental evidence for the underscreened Kondo effect, an incomplete compensation of a quantized magnetic moment by conduction electrons, as originally proposed by Nozières 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 the magnetic field that we confirm on the basis of numerical renormalization group calculations.

Domaines: Autre [cond-mat.other]

Nicolas Roch, Serge Florens, Theo A. Costi, Wolfgang Wernsdorfer, Franck Balestro. Observation of the Underscreened Kondo Effect in a Molecular Transistor. Physical Review Letters, 2009, 103 (19), pp.197202. ⟨10.1103/PhysRevLett.103.197202⟩. ⟨hal-00816935⟩