ELECTRICAL-NOISE SIGNATURES OF POSSIBLE VORTEX TRANSITIONS IN EPITAXIAL YBA2CU3O7 THIN-FILMS

Measurements of the electrical noise have been used to probe the vorte x dynamics in epitaxial YBa2Cu3O7 thin films at magnetic fields up to 8 T, and they display two sharp features as a function of temperature. A sharp onset of noise occurring at T-on < T-c2(H) is a new feature. A separate noise peak shows striking correlation to hysteresis previou sly observed in single crystals and is interpreted as melting. The tem perature of both features did not change over two decades in the appli ed current, indicating that they may be signatures of thermodynamic tr ansitions within the vortex state.