Magnetic flux in high Tcsuperconductors: thermal effects

Abstract

Mechanical oscillator and susceptibility measurements have been used to study the vortex transition to the reversible magnetic state in high quality single crystals of Bi_2.1Sr_1.9Ca_0.9Cu₂O_{8+ delta} , over a wide range of temperatures and fields. The data show that the transition is made in two steps, one at lower temperatures, associated to currents flowing across the Cu-O planes, and the other to currents in the planes.