Vortex-matter phase transitions inBi2Sr2CaCu2O8:Effects of weak disorder

Abstract

The vortex matter phase diagram in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} crystals is investigated by introducing very low doses of point and correlated disorder. We conclude that at least three distinct phases are present. The ordered low-field quasilattice phase has a finite shear modulus which vanishes at the first-order melting or sublimation transition at elevated temperatures. At lower temperatures the quasilattice transforms into a disordered solid as field is increased above the second magnetization peak. This disorder-driven transition shifts to lower fields with increased point disorder. The first-order transition displays corresponding downward curvature in the vicinity of the critical point. {copyright} {ital 1997} {ital The American Physical Society}