Vortex liquid in single-crystal ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${)}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ of varying anisotropy

The vortex liquid has been studied in single-crystal ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Fe}}_{\mathit{x}}$ ${)}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ in magnetic fields up to 8 T parallel to the c axis both with a dc-flux transformer-contact configuration and by measuring the c-axis resistivity. With current along the ab planes, the c-axis resistance drops to zero and the voltages on different ab planes become equal at a temperature ${\mathit{T}}_{\mathit{br}}$(B). With increasing anisotropy, ${\mathit{T}}_{\mathit{br}}$(B) decreased in agreement with a recent theory by Daemen et al. for a Josephson-coupled layered superconductor. The results for current injection along the ab planes and along the c axis are consistent with anisotropic local conductors for all samples.