Noise in Carbon Nanotubes in the Kondo regime

Christophe Mora (1) , T. Delattre (1) , C. Feuillet-Palma (1) , L. G. Herrmann (1) , P. Morfin (1) , J.-M. Berroir (1) , G. Fève (1) , B. Plaçais (1) , D.C. Glattli (1, 2) , M.-S. Choi , T. Kontos (1)

1 LPA - Laboratoire Pierre Aigrain
2 SPEC - UMR3680 - Service de physique de l'état condensé

The Kondo effect is a very active subject in condensed matter physics and a paradigm for strongly correlated electronic system s. It arises as a resonant antiferromagnetic coupling between the spin of an impurity with the spin of the conduction electrons in the host matrix. In nanoscale conductors like carbon nanotube devices, the spin impurity is formed in a strong Coulomb blockade region where charge is quenched. Such artificial impurities offer new perspectives for the study of the Kondo effect, in particular in out-of-equilibrium situations. We report here on {\it current noise} measurements in a carbon nanotube quantum dot tuned to the Kondo regime. A strong enhancement of the current noise is observed within the Kondo resonance compared to simple non-interacting theories. While the measured conductances come close to the unitary limit $2 e^2/h$, the noise is not suppressed as in a coherent conduc tor but remains sizeable. This effect can not be accounted for, either by a resonant level model, or by a simple SU(2) Kondo mode l. This emphasizes the importance of the doubly degenerate orbital degree of freedom (in addition to the spin degeneracy) in the dot related to clockwise and counterclockwise motion around the nanotube. Moreover, the addition of this orbital pseudo-spin with the true spin could lead to Kondo screening with an enhanced SU(4) symmetry. In fact, using an interacting slave-boson mean field (SBMFT) approach with SU(4) symmetry to describe the Kondo effect, we can account~\cite{delattre:09} for both conductance and noise measurements with a rather good agreement. Noisy Kondo impurities Nature Physics 5 (2009) 208-212

Domaines: Systèmes mésoscopiques et effet Hall quantique [cond-mat.mes-hall]

Christophe Mora, T. Delattre, C. Feuillet-Palma, L. G. Herrmann, P. Morfin, et al.. Noise in Carbon Nanotubes in the Kondo regime. The 18th International Conference on Electronic Properties of Two-Dimensional Systems (EP2DS-18), Jul 2009, Kobe, Japan. ⟨hal-00523654⟩