Magnetic studies on the field-driven transition from decoupled to coupled pancake vortex phase inBi2Sr2CaCu2O8+δwith columnar defects

Abstract

The reversible ${(M}_{\mathrm{rev}})$ and the irreversible magnetization of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals with columnar defects were measured as a function of field and temperature. In contrast to the conventional $\mathrm{ln}B$ dependence of ${M}_{\mathrm{rev}}$ observed in the unirradiated sample, the field dependence of ${M}_{\mathrm{rev}}$ for the irradiated samples exhibits an anomalous dip, corresponding to the expulsion of vortices from the sample. We show that the coupling transition, which, to our knowledge, has not been considered previously in analyzing the magnetization data, is very important to understand the anomalous behavior of ${M}_{\mathrm{rev}}.$ From the measurement, we obtain the almost temperature-independent transition line ${B}_{\mathrm{cp}}(T)\ensuremath{\sim}{B}_{\ensuremath{\Phi}}/3$, where ${B}_{\ensuremath{\Phi}}$ is a matching field. This is in good accordance with the recent computer simulation. The anomalous peak effect is observed at the same field, $B\ensuremath{\sim}{B}_{\ensuremath{\Phi}}/3$, in Bose-glass (BG) regime, which accompanies the reentrant behavior of BG melting line.