Abstract Submitted to the    NANOTUBE'04 Conference:

The strong spin coherence in carbon nanotubes (CNs) has been well-studied and proven to exist, leading to a variety of spin-phase interference effects and spintronics. Even at high magnetic fields, the spin phase itself is still preserved. On the other hand, the strength of the coherence of Cooper pairs have never been reported in CNs, although three groups[1] have reported the successful injection of Cooper pairs into carrier–undoped CNs from superconductor electrodes (proximity-induced superconductivity; PIS) and intrinsic superconductivity.

Here, we investigated the behaviors of magnetoresistance and upper critical fields, where Cooper pairs are broken by magnetic fields, in Nb/dirty multi-walled CN(MWNTs)/Al junctions within PIS. We report that the leaked Cooper pairs into the dirty MWNTs are primarily responsible for these behaviors and that this causes the suppression of Cooper-pair breaking against the applied high fields. Observations of the behaviors of the upper critical fields reveal the formation of quasi-multi-layered superconductors, consisting of proximity-induced superconductive shells/normal conductive shells, in the MWNTs. We find that the suppression becomes significant in the one-dimensional anisotropic dirty MWNTs. This is a manifestation that MWNTs can strongly maintain Cooper-pairs against high fields.

[1] J.Haruyama, S.Miyadai, et al., Phys.Rev.B 68, 165420 (2003); Appl.Phys.Lett. In press