AVS 46th International Symposium
    Topical Conference on Emerging Opportunities and Issues in Nanotubes and Nanoelectronics Thursday Sessions
       Session NT+NS+EM+MS-ThM

Paper NT+NS+EM+MS-ThM3
Electrical Transport in Single-Wall Nanotube Rings: Coherence and Localization

Thursday, October 28, 1999, 9:00 am, Room 6C

Session: Nanotubes: Nanoelectronics and Field Emission
Presenter: Ph. Avouris, IBM T.J. Watson Research Center
Authors: H.R. Shea, IBM T.J. Watson Research Center
R. Martel, IBM T.J. Watson Research Center
Ph. Avouris, IBM T.J. Watson Research Center
Correspondent: Click to Email
Understanding electrical transport in carbon nanotubes is essential for their possible use in nanoelectronics. Furthermore single-walled carbon nanotubes (SWNTs) provide ideal model systems on which to test theories of transport phenomena in 1D-systems. Linear SWNTs, however, do not have self-folding electron trajectories which can enclose magnetic flux. Thus, the technique of magneto-resistance (MR) cannot be applied directly to obtain information on the mechanism of electrical transport. Recently, we have developed a procedure by which linear SWNTs can be induced to form ring structures. Despite the high flexural rigidity of these materials, coils stabilized only by van der Waals forces can be produced in yields of ~50 %. These rings provide an ideal geometry for MR measurements. The MR is negative over the range of 0-5 T and from it we are able to determine the coherence length of the electrons in the rings. We found that over the entire range of 3 K - 60 K the SWNT-rings are in a state of weak localization induced by the constructive interference of electron waves propagating in opposite directions around the ring. Electric transport is not ballistic, and the coherence length reaches 520 nm at 3 K. From the temperature dependence of the coherence length we determine that the dominant dephasing mechanism at low T involves electron-electron interactions (Nyquist mechanism). Below ~1 K we observe an electronic phase transition to a strongly localized state. This transition is accompanied by the opening of a small energy gap and very strong MR and universal conductance fluctuations. An interesting zero bias anomaly (ZBA) is also observed below ~0.7 K. This ZBA is sensitive to magnetic fields and is ascribed to Kondo-type scattering from localized magnetic moments.