Vortex quasiordered-disordered solid transition in strongly underdoped Bi₂Sr₂CaCu₂O_8+x single crystals

The dynamic behavior of the magnetization around the second peak was studied for strongly underdoped Bi₂Sr₂CaCu₂O_8+x single crystals by the local Hall probe technique. The strong material anisotropy results in a very low second peak field, as low as 65 G. The second peak in the magnetization curves is identified as the sudden change of the flux creep energy barrier versus screening current. This indicates the different electrodynamics of the low-field quasiordered versus the high-field disordered phase.