Resonant Ultrasound Spectroscopy on Sr₂RuO₄

Sr₂RuO₄ is believed to be a possible candidate for a spin-triplet superconductor. The superconducting order parameter of Sr₂RuO₄ has been the subject of extensive research for quite some time, although reaching a consensus has been primarily limited by the difficulty to do bulk sensitive measurements of the order parameter symmetry. We performed resonant ultrasound measurements on Sr₂RuO₄ to study the evolution of all its elastic moduli down to low temperatures and through T_C. Since different symmetry order parameters couple differently to the various shear and compressional modes, measurement of all the moduli can reveal the symmetry of the order parameter. Our experiment thus gives insight on the possible pairing symmetry of the Cooper pairs in this material.