Surface Enhancement of Superconductivity in Tin
  The possibility of surface enhancement of superconductivity is examined experimentally. It is shown that single crystal tin samples with cold-worked surfaces represent a superconductor with a surface-enhanced order parameter (or negative surface extrapolation length b), whose magnitude can be controlled. 
V. F. Kozhevnikov, M. J. Van Bael, W. Vinckx, K. Temst, C. Van   Haesendonck and J. O. Indekeu (Katholieke Universiteit Leuv...