Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...

Talks Wednesday February 6
Level structure and tunnel coupling of carbon nanotube quantum dots
Kasper Grove-Rasmussen, University of Copenhagen, Denmark
We present our current understanding of the quantum states in a carbon
nanotube quantum dot deduced from low temperature transport measurements
in parallel and perpendicular magnetic fields. The observed energy
spectrum is shown to be ordered in shells of two doublets consistent with a
single-particle four-state model including spin-orbit interaction, intra-shell
valley mixing and an orbital g-factor. To fully capture the behavior in the
multi-shell case, additional inter-shell valley mixing parameters are needed,
describing valley mixing between states belonging to different shells [1, 2].
Furthermore, for certain shells, the two doublets are observed to be differently
coupled to the leads, resulting in gate-dependent level renormalization.
By comparison to the one-shell model this is shown to be a consequence
of intra-shell valley mixing in the nanotube. Moreover, a parallel magnetic
field is shown to reduce this mixing and thus suppress the effects of tunnelrenormalization
[3].
[1] T. Sand Jespersen, K. Grove-Rasmussen, J. Paaske, K. Muraki, T. Fujisawa,
J. Nygård, and K. Flensberg, Nat. Phys. 7, 348 (2011).
[2] T. S. Jespersen, K. Grove-Rasmussen, K. Flensberg, J. Paaske, K.
Muraki, T. Fujisawa, and J. Nygård, Phys. Rev. Lett. 107, 186802 (2011)
[3] K. Grove-Rasmussen, S. Grap, J. Paaske, K. Flensberg, S. Andergassen,
V. Meden, H. I. Jørgensen, K. Muraki, and T. Fujisawa, Phys. Rev. Lett.
108, 176802 (2012).
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