Giant resistive peak close to the superconducting transition in ${\mathit{L}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_4$ single crystals

We have measured the magnetoresistivity of some ${\mathit{L}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$ (L=Pr,Nd,Sm) superconducting single crystals along the ab plane and the c axis. For most crystals the resistivity along both directions displays a very sharp rise just below ${\mathit{T}}_{\mathit{c}}$ and before the zero-resistance state is reached. This resistance anomaly is quenched by a magnetic field. The effect of the field is more pronounced for H∥c than for H∥(ab). Several possible scenarios to account for the resistance anomaly are discussed. We propose that the resistance peak is a manifestation of a quasireentrant behavior resulting from an intrinsic granularity of these n-type high-temperature superconductors. The relevance of these results and ac susceptibility measurements for the anomalous behavior reported for the upper critical field is discussed.