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HL: Halbleiterphysik

HL 2: Symposium: Kondo Physics in Quantum Dots

HL 2.6: Fachvortrag

Montag, 26. März 2001, 13:00–13:30, S2

Kondo effect in carbon nanotube quantum dots — •Jesper Nygard¹, David H. Cobden², and Poul Erik Lindelof¹ — ¹Niels Bohr Institute, Ørsted Laboratory, Universitetsparken 5, DK-2100 Copenhagen, Denmark — ²Department of Physics, University of Warwick, Coventry CV4 7AL, UK

Transport experiments on individual carbon nanotubes have allowed the exploration of numerous interesting quantum effects for the first time in a molecular system [1]. For single-wall nanotubes, the behavior at low temperature is often dominated by Coulomb blockade effects due to tunnel barriers formed between the nanotubes and the attached metallic electrodes. We have obtained low-resistance contacts to single-wall nanotubes, enhancing the higher-order cotunneling processes, and have observed the Kondo effect in such a quantum dot [2]. Here, a resonance for transmission exists at low temperature due to the formation of a many-body state involving an unpaired spin on the tube and the conduction electrons in the gold leads. The one-dimensionality of nanotubes makes the effect particularly pronounced, with Kondo temperatures up to 2 K and for large electron number N. The effect exist only for odd N, reflecting even-odd alternations due to spindegeneracy. However, at finite magnetic field an effect induced by a singlet-triplet degeneracy is observed for even N. [1] Dekker, C., Physics Today 52, 22 (June 1999). [2] Nygard, J., Cobden, D.H., and Lindelof, P.E., Nature 408, 342 (2000).