Phase-sensitive test of odd-parity superconductivity in Sr$_{2}$RuO$_{4}$

The possibility of odd-parity, spin-triplet pairing of electrons was first pointed out in 1960 after the publication of the BCS theory for superconductivity. Sr$_{2}$RuO$_{4}$, the only Cu-free layered perovskite superconductor, was predicted to be a material featuring such an unusual pairing state. We have in the past several years pursued the phase-sensitive test of odd-parity pairing in Sr$_{2}$RuO$_{4}$ following the proposal of Geshkenbein, Larkin, and Barone (GLB). The experiment involves the preparation and the measurement of GLB SQUIDs consisting two oppositely faced Josephson junctions between an s-wave superconductor, Au$_{0.5}$In$_{0.5}$, and Sr$_{2}$RuO$_{4}$ as well as control samples. We found that the critical current of GLB SQUIDs was a maximum while for control samples of SQUIDs with two junctions prepared on the same side, the critical current is a minimum at zero magnetic flux. This indicates that the phase of the order parameter changes by \textit{$\pi $} under inversion, showing that Sr$_{2}$RuO$_{4}$ is indeed an odd-parity superconductor [1]. More recent results on corner and the same-side junctions of Au$_{0.5}$In$_{0.5}$-Sr$_{2}$RuO$_{4}$ will be presented. [1] K.D. Nelson, Z.Q. Mao, Y. Maeno, and Y. Liu, Science 306, 1151-1154 (2004).