UNIVERSALITY OF FREQUENCY AND FIELD SCALING OF THE CONDUCTIVITY MEASURED BY AC SUSCEPTIBILITY OF A YBA2CU3O7 FILM

Utilizing an exact inversion scheme, we determine the complex linear c onductivity sigma(omega) of a YBa2Cu3O7 film from the linear magnetic ac susceptibility which has been measured from 3 mHZ to 50 MHz in fiel ds between 0.4 and 4 T applied parallel to the c axis of a 250-nm thin disk. The frequency derivative of the phase sigma''/sigma' and the dy namical scaling of sigma(omega) above and below T(g)(B) provide clear evidence for a continuous phase transition at T(g) to a generic superc onducting state. Based on the vortex-glass scaling model, the resultin g critical exponents nu and z are close to those frequently obtained o n films by other means and associated with an isotropic vortex glass. The field effect on sigma(omega) can be related to the increase of the glass coherence length, xi(g) approximately B.