Mott insulating state in ultraclean carbon nanotubes
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.
Additional Information© 2009 American Association for the Advancement of Science. We acknowledge Micro Nano Laboratory at Caltech and Nanotech at the University of California, Santa Barbara where fabrication was performed. We thank A. Andreev, D. Cobden, M. Garst, L. Glazman, S. Ilani, P. King, K. Le Hur, L. Levitov, G. Refael, and G. Steele for helpful discussions. M.B. and V.V.D. acknowledge the support of the Office of Naval Research, the Sloan Foundation, and the Ross Brown. D.N. was supported by NSF grants DMR-0749220 and DMR-0754613.
Supplemental Material - DESsci09supp.pdf