Carbon Nanotube Quantum Dots: from the Coulomb Blockade to the SU(4) Kondo and the Mixed Valence regimes
|Location: Fachbereich Physik, SR E3
Time: Friday 24.08.2007, 14h c.t.
Carbon nanotubes present an ideal system for investigating quantum electronic transport at the nanoscale. By controlling the contact transparency within the same nanotube Quantum Dot, we can observe the conductance evolution from the well-developed Coulomb blockade through the Kondo regime to the 'Mixed Valence' regime. We work with high quality nanotubes, where quantum-mechanical orbitals are doubly-degenerate, forming four-electron 'shells', so that the system possesses an SU(4) symmetry. We observe the SU(4) Kondo effect for one, two, and three electrons in a shell. As the contacts are made more transparent, the sample enters the 'Mixed Valence' regime, where different charge states are hybridized by electron tunneling. The hallmark of the new regime is the surprising lack of single-electron features at low temperature, which are uncovered as the temperature is raised.
More information: F. von Oppen (vonoppenphysik.fu-berlin.de)
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