Carbon nanotubes present an attractive system for studying quantum electronic transport. 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.
Coffee and cookies before the presentation at 3:15 pm, and refreshments after the presentation will both be served in Room 128.