Long range coupling in YBa₂Cu₃O_7−δ/Y_1−xPr_xBa₂Cu₃O_7−δ multilayers

Abstract

YBa₂Cu₃O_7−δ/(Y_1−xPr_x)Ba₂Cu₃O_7−δ multilayers have been used to probe coupling through (Y_1−x:Pr_x)Ba₂Cu₃O_7−δ alloys. We observe that the coupling between ultrathin YBa₂Cu₃O_7−δ layers, 12 or 24 Å thick, survives through several hundred Å of (Y_1−xPr_x)Ba₂Cu₃O_7−δ with x=0.4 and 0.55. T_c versus the thickness of the spacer-alloy, and activation energies for flux motion, with fields parallel and perpendicular to the c-axis, have been used to probe this long range coupling. All these experiments point to an unusually large coupling length for these two alloy compositions. In the x=0.55 case this result is particularly surprising since the alloy material display a semiconducting behaviour for this composition. T_c measurements, activation energies, and a study of the vortex dynamics in these coupled multilayers is presented along with new results obtained on a series of multilayers built with a more insulating alloy, x=0.7.