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Science 2 January 2009:
Vol. 323. no. 5910, pp. 106 - 110
DOI: 10.1126/science.1165799
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Reports

Mott Insulating State in Ultraclean Carbon Nanotubes

Vikram V. Deshpande,1* Bhupesh Chandra,2 Robert Caldwell,3 Dmitry S. Novikov,4 James Hone,2{dagger} Marc Bockrath1{dagger}

The Mott insulating state is a manifestation of strong electron interactions in nominally metallic systems. Using transport spectroscopy, we showed that an energy gap exists in nominally metallic carbon nanotubes and occurs in addition to the band gap in small–band-gap nanotubes, indicating that carbon nanotubes are never metallic. This gap has a magnitude of ~10 to 100 milli–electron volts and a nanotube radius (r) dependence of ~1/r, which is in good agreement with predictions for a nanotube Mott insulating state. We also observed neutral excitations within the gap, as predicted for this state. Our results underscore nanotubes' exceptional capabilities for use in studying correlated electron phenomena in one dimension.

1 Applied Physics, California Institute of Technology, Mail Stop 128-95, Pasadena, CA 91125, USA.
2 Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.
3 Department of Applied Physics, Columbia University, New York, NY 10027, USA.
4 Department of Physics, Yale University, New Haven, CT 06511, USA.

* Present address: Department of Physics, Columbia University, New York, NY 10027, USA.

{dagger} To whom correspondence should be addressed. E-mail: mwb{at}caltech.edu (M.B.); jh2228{at}columbia.edu (J.H.)

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Coupling Strongly, Discretely.
J. Hone and V. V. Deshpande (2009)
Science 325, 1084-1085
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