Evolution of SU(4) Transport Regimes in Carbon Nanotube Quantum Dots

Abstract

We study the evolution of conductance regimes in carbon nanotubes with doubly degenerate orbitals (``shells'') by controlling the contact transparency within the same sample. For sufficiently open contacts, Kondo behavior is observed for 1, 2, and 3 electrons in the topmost shell. As the contacts are opened more, the sample enters the ``mixed valence'' regime, where different charge states are strongly hybridized by electron tunneling. Here, the conductance as a function of gate voltage shows pronounced modulations with a period of four electrons, and all single-electron features are washed away at low temperature. We successfully describe this behavior by a simple formula with no fitting parameters. Finally, we find a surprisingly small energy scale that controls the temperature evolution of conductance and the tunneling density of states in the mixed valence regime.

4 pages + supplementary info. The second part of the original submission is now split off as a separate paper (0709.1288)

References in corpus (7)

• Orbital Kondo effect in carbon nanotubes
• Kondo effect in quantum dots
• Nonequilibrium Singlet-Triplet Kondo Effect in Carbon Nanotubes
• Four-electron shell structures and an interacting two-electron system in carbon nanotube quantum dots
• Quantum phase transition in capacitively coupled double quantum dots
• Electronic Transport Spectroscopy of Carbon Nanotubes in a Magnetic Field
• Electronic excitation spectrum of metallic carbon nanotubes

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