Measurement of a weak-link Josephson junction in a p-wave superconducting ring

We report the fabrication of a weak-link Josephson junction in a micron-size Sr ₂ Ru O₄ ring by focused ion beam milling, and the measurement of the current-phase relation (CPR) using cantilever torque magnetometry. In the presence of a magnetic field applied perpendicular to the crystal c - axis, a second harmonic term in the CPR appears which may be related to the underlying spin texture of the spin-triplet condensate. The observed CPR is similar to that previously reported for weak-link junctions in ³ He-B. By including the contribution from both the charge and the spin current into the Gibbs-free energy, we can accurately model the observed CPR of the Sr ₂ Ru O₄ weak-link junction.