The « irreversibility line » of Bi2-xPbxSr2Ca2Cu3O10 : a possible breakdown of an intrinsic proximity effect

Abstract

The study of the magnetization « irreversibility line » of a Bi2-xPbxSr2Ca2Cu3O10 compound with a critical temperature T c of 110 K is presented. At low temperatures, we observe H* ∼ e-T/T0 and close to Tc, H* ∼ (1 - T/Tc) 3/2. The reversible magnetization as a function of the magnetic field H obeys the laws calculated for the Abrikosov flux lattice of an ideal superconductor when Hc1 ⪡ H ⪡ Hc2. Even far from Tc, magnetization decreases linearly with T. The exponential behavior of H*(T) can be interpreted by the existence of a breakdown field in which a proximity effect induced superconductivity is destroyed. The structure may be seen as a superlattice composed of laminae alternatively normal and superconducting. The normal laminae could be the SrO-BiO-BiO-SrO layers, the superconducting ones being the 3 CuO layers. The strong dependence of the critical current with magnetic field is explained by the weakening of the correlation energy of vortices at the phase transition corresponding to the breakdown by the magnetic field of an induced superconductivity in the normal laminae