DIVERGING TIME SCALES FOR ONSET OF IRREVERSIBILITY IN HIGH-TEMPERATURE SUPERCONDUCTORS

The onset temperature, T(irr) for magnetic irreversibility in high-tem perature superconductors has been investigated as a function of freque ncy (0.2 Hz less-than-or-equal-to f less-than-or-equal-to 65 000 Hz) a nd DC magnetic field (0<H< 4000 Oe). In Y-Ba-Cu-O crystals T(irr) is e ssentially independent of the frequency, while in Bi-Sr-Ca-Cu-O and TI -Ba-Ca-Cu-O crystals T(irr) exhibits a strong frequency dependence. Fo r all three systems T(irr)(H) converges to a finite temperature as the frequency approaches zero. Analysis of the experimental data shows th at conventional theories of thermally-activated vortex motion cannot e xplain the measured frequency dependence of T(irr) Rather, the data in dicate that T(irr) for f --> 0 can be interpreted as a transition temp erature separating the reversible vortex-liquid and the irreversible v ortex-glass phases.