Experimental observation of non-s-wave superconducting behavior in bulk superconducting tunneling junctions of YBa2Cu3O7−δ and Bi2Sr2CaCu2O8+δ

Abstract

One of the thrusts of high-Tc superconductor research today is to determine the pairing mechanism of these materials. We present here, experimental observations of non-'s-wave' superconducting behavior in both YBa₂Cu₃O_7−δ (Y-123) and Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) bulk superconducting tunneling junctions. Near single-phase bulk samples of Y-123 and Bi-2212 were prepared, on which planar contact tunneling experiments have been performed at 77.0 Kelvin. The I-V plots obtained, for both superconductors, show no evidence of a clear superconducting energy gap − a direct consequence of an s-wave superconducting mechanism approximation. instead, the dI/dV-V plots obtained exhibit structures in the form of 'cusps' which is a strong indication of d-wave superconductivity. Our theoretical calculations, based on a 'd-wave' approximation, show good agreement with the experimental dI/dV-V plots obtained. These results favor a d-wave character for the pairing symmetry of these high-Tc superconductors.