Letter abstract
Nature Physics 2, 460 - 464 (2006)
doi:10.1038/nphys340
Subject Categories: Condensed-matter physics | Electronics, photonics and device physics | Nanotechnology
Non-equilibrium singlet–triplet Kondo effect in carbon nanotubes
J. Paaske1, A. Rosch2, P. Wölfle3, N. Mason4,5, C. M. Marcus5 and J. Nygård1
The Kondo effect is a many-body phenomenon arising due to conduction electrons scattering off a localized spin1. Coherent spin-flip scattering off such a quantum impurity correlates the conduction electrons, and at low temperature this leads to a zero-bias conductance anomaly2, 3. This has become a common signature in bias spectroscopy of single-electron transistors, observed in GaAs quantum dots4, 5, 6, 7, 8, 9 as well as in various single-molecule transistors10, 11, 12, 13, 14, 15. Although the zero-bias Kondo effect is well established, the extent to which Kondo correlations persist in non-equilibrium situations where inelastic processes induce decoherence remains uncertain. Here we report on a pronounced conductance peak observed at finite bias voltage in a carbon-nanotube quantum dot in the spin-singlet ground state. We explain this finite-bias conductance anomaly by a non-equilibrium Kondo effect involving excitations into a spin-triplet state. Excellent agreement between calculated and measured nonlinear conductance is obtained, thus strongly supporting the correlated nature of this non-equilibrium resonance.
- The Niels Bohr Institute & The Nano-Science Center, University of Copenhagen, DK-2100 Copenhagen, Denmark
- Institut für Theoretische Physik, Universität zu Köln, 50937 Köln, Germany
- Institut für Theorie der Kondensierten Materie, Universität Karlsruhe, 76128 Karlsruhe, Germany
- Department of Physics, University of Illinois at Urbana Champaign, Urbana, Illinois 61801-3080, USA
- Department of Physics, Harvard University, Cambridge, Massachusetts 0213, USA
Correspondence to: J. Paaske1 e-mail: paaske@fys.ku.dk
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