Metastability line in the phase diagram of vortices in Bi2Sr2CaCu2O8

Nonlinear transport in the low-temperature vortex glass state of single cry stal Bi2Sr2CaCu2O8 has been investigated with fast current pulses driven al ong the ab plane. Field cooled preparation shows a higher threshold current (marking a jump or break in slope in the voltage response) than the zero f ield cooled (ZFC) one, but it is found to be metastable and convertible to the ZFC response by a small field excursion. The metastability appears on t he low temperature side of the peak in the temperature dependence of the ZF C threshold current. It is suggested that the onset of metastability signal s a different thermodynamic ground state.