Thermal fluctuations and vortex melting in the classical superconductor   Nb3Sn from high-resolution specific-heat measurements
  The range of critical thermal fluctuations in classical bulk superconductors is extremely small and especially in low fields hardly experimentally inaccessible. With a new type of calorimeter we have been able to resolve a small lambda anomaly within a narrow temperature range around the Hc2 line. We show that the evolution of the anomaly as a function of magnetic field follows scaling laws expected in the presence of critical fluctuations. The lower onset of the fluctuation regime shows many characteristics of a continuous solid-to-liquid transition in the vortex matter. It can be driven into a first-order vortex melting transition by a small AC field which helps the vortex matter to reach equilibrium. 
R. Lortz, F. Lin, N. Musolino, Y. Wang, A. Junod, B. Rosenstein, N.   Toyota