Vortex phase transition and vortex state in (La0.954Sr0.046)2CuO4 single crystals

The vortex state above and below the first order transition was examined in (La0.954Sr0.046)2CuO4 single crystals by means of magnetization and two types of transport measurements. The vortex fluctuations were found to have pronounced effects in the fluid region, which was observed as a smaller slope (∂M/∂lnH) of the reversible magnetization curve in the vortex fluid than that in the solid, and as an increase of the difference between them with temperature. In addition, transport measurements with the transformer-type electrode configuration revealed a drastic decrease of the vortex velocity correlation along the field in the fluid phase. Both results were consistent with a vortex lattice state in the solid phase and a highly fluctuating pancake-vortex state in the fluid phase