Field-induced suppression of the phase transition in Bi₂Sr₂CaCu₂O₈

Magnetization measurements in field on a Bi₂{Sr}₂CaCu₂{O}₈$ single crystal do not reveal any sharp phase transition between the normal and superconducting states. The M(H) curves for temperatures about ${T}c$ in fields up to 5 T all display diamagnetic behavior. Above the mean-field transition temperature ${T}cMF$, quasi-two-dimensional diamagnetic fluctuations are responsible. Below ${T}cMF$ strong deviations from the conventional mean-field (Abrikosov) behavior lead to an apparent ${T}c$(B) inadequacy of the mean-field theory to describe the vortex state below the crossover line ${H}c2$(T).