  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.

Superconductivity