Depairing field, onset temperature and the nature of the transition in cuprates

The depairing (upper critical) field Hc2 in hole-doped cuprates has been inferred from magnetization curves M–H measured by torque magnetometry in fields H up to 45 T. We discuss the implications of the results for the pair binding energy, onset temperature, fluctuation diamagnetism and the nature of the Meissner transition at Tc.