title: Even-odd effect in Andreev transport through a carbon nanotube quantum dot.
abstract: We have measured the current (I)-voltage (V) characteristics of a single-wall carbon nanotube quantum dot coupled to superconducting source and drain contacts in the intermediate coupling regime. Whereas the enhanced differential conductance dI/dV due to the Kondo resonance is observed in the normal state, this feature around zero-bias voltage is absent in the superconducting state. Nonetheless, a pronounced even-odd effect appears at finite bias in the dI/dV subgap structure caused by Andreev reflection. The first-order Andreev peak appearing around V=Delta/e is markedly enhanced in gate-voltage regions, in which the charge state of the quantum dot is odd. This enhancement is explained by a "hidden" Kondo resonance, pinned to one contact only. A comparison with a single-impurity Anderson model, which is solved numerically in a slave-boson mean-field approach, yields good agreement with the experiment.
authors.affiliation: Institut für Physik, Universität Basel, Klingelbergstr. 82, CH-4056 Basel, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Eichler
authors.forename: M
authors.initials: M
authors.lastname: Weiss
authors.forename: S
authors.initials: S
authors.lastname: Oberholzer
authors.forename: C
authors.initials: C
authors.lastname: Schönenberger
authors.forename: A
authors.initials: A
authors.lastname: Levy Yeyati
authors.forename: J C
authors.initials: JC
authors.lastname: Cuevas
authors.forename: A
authors.initials: A
authors.lastname: Martín-Rodero