Vortex Phase Diagram in Zn-Doped YBa2Cu3O y Crystals

Effects of Zn impurities on the vortex phase diagram of YBa₂(Cu_1–x Zn _x )₃O _y single crystals with 0x0.064 have been investigated in magnetic field up to 18 T. The first-order vortex lattice melting transition and the field-driven disordering transition are extremely suppressed by small amount of Zn impurities. As for Zn-doped YBCO with x>0.001, the resistive transition shows a broad temperature dependence due to the second-order vortex glass melting transition, while the field-driven disordering transition survives up to 0.003. These behaviors suggest that disorderes induced by Zn impurities strongly affect the vortex system in comparison with the oxygen deficiency in YBCO.