Some improved geometries for Josephson-junction investigations of the order-parameter symmetry in high-Tc superconductors

Abstract

We propose two new geometries for Josephson junction experiments between the edge of an orthorhombic, untwinned single-crystal high-Tc superconductor, assumed to have an order parameter of the mixed s±dx2−y2 variety, and a conventional, s-wave superconductor. The first geometry is a straight-edge Josephson junction cut at an angle φ0 with respect to the a-axis edge of a high-Tc crystal. We studied the effects of a regular array of a/b steps comprising the edge upon the Ic(B) pattern for different φ0 values. Varying φ0 can elucidate the locations of any purported order-parameter nodes. The second geometry is a disk cut from a high-Tc single crystal, with a Josephson junction formed on the edge, centered at φ0, with an angular width of Δφ. The case Δφ=π is nearly free of systematic flux trapping problems, and is shown to be particularly important in quantifying the precise amount of s/d order-parameter mixing. Smaller Δφ values can also be useful in locating the purported order-parameter nodes.

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