We report superconducting resistive transition characteristics for array(s) of coupled $4\text{Å}$ single wall carbon nanotubes embedded in aluminophosphate-five zeolite. The transition was observed to initiate at 15 K with a slow resistance decrease switching to a sharp, order of magnitude drop at $\sim 7.5\text{K}$. The latter exhibits anisotropic magnetic field dependence, and the differential resistance versus current (voltage) measurements show a rich variety of details that are consistent with the establishment of coherence, in stages, as the temperature is lowered below 15 K. In particular, the resistance drop that starts at 7.5 K exhibits attributes that are consistent with the manifestations of a Berezinskii-Kosterlitz-Thouless transition that establishes quasi-long-range order in the plane transverse to the $c$ axis of the aligned nanotubes.

• Received 9 April 2010

DOI:https://doi.org/10.1103/PhysRevB.81.174530