title: Observation of the underscreened Kondo effect in a molecular transistor.
abstract: 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.
authors.affiliation: Institut Néel, associé à l'UJF, CNRS, BP 166, 38042 Grenoble Cedex 9, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Roch
authors.forename: Serge
authors.initials: S
authors.lastname: Florens
authors.forename: Theo A
authors.initials: TA
authors.lastname: Costi
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wernsdorfer
authors.forename: Franck
authors.initials: F
authors.lastname: Balestro