Even-odd effect in Andreev transport through a carbon nanotube quantum dot.
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.
Eichler
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Institut für Physik, Universität Basel, Klingelbergstr. 82, CH-4056 Basel, Switzerland.
Weiss
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Oberholzer
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S
Schönenberger
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Levy Yeyati
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Cuevas
J C
JC
Martín-Rodero
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