Thermal fluctuations in the classical superconductor Nb3Sn from high-resolution specific-heat measurements

The range of thermal fluctuations in ‘classical’ bulk superconductors is extremely small and especially in low-fields hardly experimentally accessible. With a new type of calorimeter we were able to detect a tiny lambda anomaly in the specific-heat of the superconductor Nb3Sn 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 thermal fluctuations.