Resistivity and upper critical field of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_{3\mathrm{-}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ single crystals

We report the resistivity and the upper critical field ${\mathit{H}}_{\mathit{c}2}$(T) of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_{3\mathrm{-}\mathit{x}}$ ${\mathrm{Fe}}_{\mathit{x}}$ ${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ single crystals. In the normal state, no magnetoresistivity is observed within experimental sensitivity in our measurement. The superconducting transition is broadened by the magnetic field. The upper-critical-field slope decreases as the iron composition increases. Based on these experimental results, we estimate the superconducting coherence length and the anisotropy. A possible anomalous local-pairing mechanism in these systems is suggested.