Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 26: Transport: Graphene and Carbon Nanotubes

TT 26.12: Talk

Wednesday, March 25, 2009, 17:30–17:45, HSZ 03

Exchange effects in single wall carbon nanotube quantum dots — •Christoph Schenke, Sonja Koller, Leonhard Mayrhofer, and Milena Grifoni — Institute for Theoretical Physics, University of Regensburg

Various transport experiments have been performed on single wall carbon nanotube quantum dots (SWNTs) in recent years. Some of them revealed exchange effects - as predicted in a mean-field approach by [1]. Using the powerful technique of bosonization we were able to derive the full spectrum of interacting finite-size SWNTs. The long- and short-range parts of the Coulomb interaction are responsible for charging and exchange effects, respectively. In particular we find that the ground state of a SWNT with two electrons in the last shell can be a triplet or a singlet, depending on the magnitude of the exchange coupling. The latter is at largest for small diameter SWNTs [2].

An additionally applied parallel magnetic field induces a Zeeman-splitting between the energy levels of the system. We evaluated the current - bias voltage - gate voltage characteristics for zero and finite magnetic fields. We found a quantitative agreement with the experimental results in [3] where, in particular, a singlet-triplet crossing by sweeping the magnetic field was observed.

[1] Y. Oreg, K. Byczuk and B.I. Halperin, Phys. Rev. Lett. 85, 365 (2000).

[2] L. Mayrhofer and M. Grifoni, Eur. Phys. J. B63, 45 (2008).

[3] S. Moriyama et al., Phys. Rev. Lett. 94, 186806 (2005).