Transport properties of high-angle grain boundaries in Co-dopedYBa2Cu3O7−δthin films

Abstract

We have measured the electrical properties of symmetric 24\ifmmode^\circ\else\textdegree\fi{}-angle grain boundaries in ${\mathrm{YBa}}_{2}({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ thin films, for $x=0--0.1.$ The Josephson properties of the grain boundaries vary dramatically with the amount of Co doping and with the growth conditions. The critical current decreases and the resistance increases as Co is added until the supercurrent is suppressed. The ${I}_{c}{R}_{n}$ product scales in a similar manner as other high-${T}_{c}$ weak links. The $I\ensuremath{-}V$ characteristics become nonlinear with Co doping and often display resonant structure. An analysis of these results indicates that these grain boundaries are not well described by simple models.