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

The vortex state above and below the first order transition was examined in (La0.954Sr0.046)(2) CuO4 single crystals by means of magnetization and two types of transport measurements. The vortex fluctuations were found to hav e pronounced effects in the fluid region, which was observed as a smaller s lope (partial derivative M/partial derivative lnH) of the reversible magnet ization curve in the vortex fluid than that in the solid, and as an increas e of the difference between them with temperature. In addition, transport m easurements with the transformer-type electrode configuration revealed a dr astic decrease of the vortex velocity correlation along the field in the fl uid phase. Both results were consistent with a vortex lattice state in the solid phase and a highly fluctuating pancake-vortex state in the fluid phas e.