Vortex-matter phase diagram in YBa₂Cu₃O_<i>y</i>

Abstract

This paper reviews the progressive results of the vortex-matter phase diagram for the high-Tcsuperconductor YBa2 Cu3 Oy in magnetic fields up to 30 T. Evidence of the first-order vortex-lattice melting transition and the second-order vortex-glass transition is demonstrated by resistivity and magnetization measurements. The feature of the novel second magnetization peak is summarized and the origin of the new line H *(T ), which is defined by the sharp onset of the second peak, is discussed on the basis of the field-driven disordering transition theory. Effects of the weak point disorder on the vortex-matter phase diagram are also studied by the irradiation of 2.5 MeV electrons. It is revealed that three transition lines of the vortex-lattice melting line Hm(T), the vortex-glass transition line Hg(T), and the field-driven disordering transition line H*(T) terminate at the critical point and divide the vortex-matter phase into three different phases: the vortex liquid, the Bragg glass, and the vortex glass. Interesting similarities of the vortex matter phase diagram between YBa2Cu3Oyand Bi2Sr2CaCu2Oyare also discussed.