  We report that entirely end-bonded multi-walled carbon nanotubes (MWNTs) can
show superconductivity with the transition temperature Tc as high as 12K that
is approximately 40-times larger than those reported in ropes of single-walled
nanotubes. We find that emergence of this superconductivity is very sensitive
to junction structures of Au electrode/MWNTs. This reveals that only MWNTs with
optimal numbers of electrically activated shells, which are realized by the
end-bonding, can allow the superconductivity due to inter shell effects.
