SEQUENTIAL VORTEX STATES UPON LATTICE MELTING IN UNTWINNED SINGLE-CRYSTAL YBA2CU3O7

摘要

Simulatenous measurements of the ac susceptibility and the dc magnetization of an untwinned single-crystal YBa2Cu3O7 has been carried out to clarify the nature of vortex lattice melting. The first-order melting transition appears as a jump in the dc magnetization. Evidence of effectual pinning at temperatures above the melting transition is obtained as a sharp transition in chi' and a sharp peak in chi '' of width 0.2 K in 10 kG. In addition, a prescursor lattice softening phenomenon can be seen in chi' and chi '' at temperatures below the melting temperature. This sequential change is more visible when the ac susceptability is given the chi'-chi '' representation. It has been confirmed that there exists a melting transition of YBa2Cu3O7 even below 10 kG. [References: 17]