Effect of the magnetic field on the c-axis resistance peak in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathit{x}}$ epitaxial films

The measurements of the out-of-plane component of resistivity ${\mathrm{\rho }}_{\mathit{c}}$(T,B) in magnetic field in high-quality epitaxial ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathit{x}}$ films are presented. We found that ${\mathrm{\rho }}_{\mathit{c}}$(T,B) exhibits a well-pronounced peak at the edge of the superconducting transition. Magnetic field causes both a sizeable increase of the relative magnitude of the peak and a strong shift of its position to lower temperatures. We demonstrate that zero-field data and data for weak magnetic fields B≤1 T are well described within the fluctuation theory taking into account Gaussian approximation in fluctuation behavior. Quantitative fit of the data in the framework of this theory allowed us to extract the effective anisotropy parameter, the quasiparticle relaxation time and the phase pair-breaking relaxation time. We discuss the reasons of the discrepancy between theory and experiment for stronger magnetic fields. © 1996 The American Physical Society.