TEMPERATURE-DEPENDENCE OF UPPER CRITICAL-FIELD AND ANISOTROPY OF YBA2CU3O7

Like the conventional superconductors, the temperature dependence of u pper critical field (B-c2) and anisotropy of effective mass (gamma) of YBa2Cu3O7 can be determined from the peak position of the specific he at in magnetic fields. It is argued that the upper critical field at T = 0 K (B-c20) cannot be extrapolated from the measurement in the crit ical region. The procedure to obtain B-c2 and a possible way to extrap olate B-c20 from specific-heat measurements is presented.