Grifoni, Milena

Date: Thursday, October29, 2015
Time: 15:45
Place: ETH Zurich, Hönggerberg, HPF G 6
Host: Werner Wegscheider

Manybody excited states magnetospectroscopy in Kondo correlated carbon nanotubes

Milena Grifoni
University of Regensburg, Germany

The Kondo effec in quantum dots is an archetypical manifestation of strong electronic correlations  wherby a localized dot electron forms a highly entangled state with conduction electrons    in the leads. A degeneracy of quantum dot states required for the occurrence of the Kondo effect is usually provided by the electronic spin degree of freedom, resulting in the so-called SU(2) Kondo behavior. In carbon nanotubes (CNTs) an additional degeneracy in the energy spectrum stems from the sublattice symmetry of the graphene lattice, and enables one to study unconventional correlation phenomena such as the spin plus orbital SU(4) Kondo effect. The sublattice symmetry, though, is broken by a finite spin-orbit coupling or by a boundary induced valley mixing, and is visible in the presence of satellite Kondo peaks in the nonlinear transport. Strikingly, experiments studying  the evolution of the central Kondo peak and of its satellites in magnetic fields reveal selection rules in the inelastic virtual processes contributing to the Kondo resonance. We discuss the origin of these selection rules. Additionally, we present a novel approach to the non-equilibrium Kondo problem, based on the Keldysh effective action,  which well reproduces the rich experimental observations.