Vortex phase diagram as a function of oxygen deficiency in untwinned YBa{sub 2}Cu{sub 3}O{sub y}

Abstract

Magnetization and resistivity measurements were performed in un-twinned YBa2Cu3Oy(YBCO) single crystals with different oxygen content. We find that the vortex phase diagram is a strong function of the oxygen deficiency; (1) For fully oxidized YBCO (y ≃ 7, Tc ≃ 87.5 K), the first-order vortex lattice melting line Tm(H) is observed up to 30 T. (2) For slightly overdoped YBCO (Tc≃ 92 K), Tm(H) and the vortex glass transition line Tg(H) terminate at the multicritical point and the field-driven disordering transition line separates the vortex solid phase into the Bragg glass and the vortex glass phases. (3) For slightly underdoped YBCO (Tc≃ 92.3 K), Tg(H) terminates well below the critical point of Tm(H), indicating the existence of the vortex slush regime by the introduced oxygen deficiency.