Dimensional crossover field as a function of oxygen stoichiometry in YBa 2 Cu 3 O 7 − δ thin films

摘要: The magnetic phase diagram of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ thin films was studied as a function anisotropy by systematically changing the oxygen stoichiometry (\ensuremath{\delta} value). For small \ensuremath{\delta} values vortex-solid transition boundary ${\mathit{H}}_{\mathit{g}}$(T) is observed over full accessible field range (50 kOe) to follow (1-T/${\mathit{T}}_{\mathit{c}}$${)}^{\mathrm{\ensuremath{\sim}}1.5}$ dependence that expected for an anisotropic superconductor in three-dimensional regime. As increases, portion no longer follows making it possible identify anisotropy-dependent dimensional crossover ${\mathit{H}}_{0}$ at which system begins behave quasi-two-dimensionally. Plotting normalized (1-T/${\mathit{T}}_{\mathit{c}}$) results collapse boundaries onto single universal curve. Using published \ensuremath{\gamma}=8.5 and upper critical slope ${\mathit{dH}}_{\mathit{c}2}$/dT=-20 kOe/K determine specific relation ${\mathit{H}}_{0}$\ensuremath{\approxeq}1.2${\mathrm{\ensuremath{\varphi}}}_{0}$/(${\mathit{d}}^{2}$${\ensuremath{\gamma}}^{2}$), where d multilayer spacing, can be used \ensuremath{\gamma}.