Observation of critical scaling behavior in the ac impedance at the onset of superconductivity in a large magnetic field

We have measured the ac impedance of Y-Ba-Cu-O thin films in a magnetic field of 0.55 T and in the frequency range from 100 kHz to 500 MHz. At the temperature of the dc vortex-glass transition but in the ac linear regime, we find scaling behavior of the impedance amplitude.