Specific Heat of Superconducting Fine Particles of Tin. II. Fluctuations under Magnetic Field, Critical Field and Transition Temperature

Electronic specific heats under a magnetic field up to 30 kOe have been measured on ensembles of fine particles of Sn with the average radius ranging 190–500 A over the temperature range of 1.5–6.0 K. In low fields, the broadening of the superconducting transition is explained by thermodynamical fluctuations on the assumption that they depend on a magnetic field only through the change of T c . With increasing field, the particle-size distribution becomes dominant in the broadening. Temperature- and size-dependences of the critical field are in good agreement with the de Gennes-Tinkham theory. The enhancement of T c of small particles in zero field is explained by the softening of the surface phonons.