ON THE PHASE-TRANSITION OF SUPERCONDUCTING CUPRATES IN ZERO AND NONZERO MAGNETIC-FIELDS

We present the results of measurements of the magnetization M(T) and t he specific heat C-p(T) of YBa2Cu3O6.9 and Bi2Sr2CaCu2O8 in the vicini ty of their respective critical temperature and in magnetic fields bet ween 0 and 5 T. From these data we calculate the temperature- and magn etic field derivatives of M and C-p. Both these measured and calculate d quantities are used for testing theoretical predictions concerning t he universality class of the transitions and to verify the influence o f fluctuations accompanying the transitions.