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

A. Makarovski·J. Liu·G. Finkelstein
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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.

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A. Makarovski, J. Liu, G. Finkelstein. 2007-09-10. Evolution of SU(4) Transport Regimes in Carbon Nanotube Quantum Dots. https://doi.org/10.1103/physrevlett.99.066801

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