Effect of nanocrystal/carbon nanotube interface on surface superconductivity of TaC encapsulated in the multiwall carbon nanotubes

The critical magnetic field Hc2 for bulk crystal TaC and that Hc3 for nanocrystal TaC encapsulated in the multiwall carbon nanotubes as a function of t (=T/Tc, Tc = 10.16 ± 0.01 K) are reported. The ratio Hc3/Hc2 below t = 0.9 exhibits a value 1.24 ± 0.06, and accords with the reports for the type-II superconductors in good contact with the normal metals. Above t = 0.9 it increases with increasing t up to 3.2 ± 0.4 at t = 0.97, and accords with the reports for the type-II superconductors surrounded by the insulators. The role of the interface between the single crystal TaC and the carbon nanotube in surface superconductivity is discussed in terms of the boundary effects.