The nanocrystal-carbon cage- interface effect on surface superconductivity in YC2 encapsulated in the multiwall carbon nanocages

The upper critical magnetic field for the vortex state, H-c2, for the bulk crystals YC2 and the critical field for the state of surface superconductivity, H-c3, for the single-crystals YC2 encapsulated in the multiwall carbon nanocages as a function of t (T/T-c T-c = 3.838 K) are reported. The ratio Hc3/Hc2 increases with increasing t from 1.6 +/- 0.2 at t = 0.6 to 2.0 +/- 0.3 at t = 0.99. The present data accord with the reported experimental results for the type-II superconductors surrounded by the insulators. The role of the interface between the single-crystal YC2 and the multiwall carbon nanocage in surface superconductivity is discussed in terms of the boundary effects. (c) 2005 Elsevier B.V. All rights reserved.