Towards microwave spectroscopy on spin-triplet collective modes

Cooper pair spin waves are a collective mode which may arise in triplet superconductors analogous to spin waves in ferromagnets [Poniatowski et. al. 129, 237002 (2022)]. Here, we develop a technique to couple this mode to the RF magnetic fields in a cylindrical microwave cavity. Implementing a "flute" cavity [Chakram et. al. PRL 127, 107701 (2021)] optimized for low-loss and compatibility with large magnetic fields, we first demonstrate that we can achieve strong coupling to spin waves in the ferromagnetic material YIG. At 14.7 GHz., we observe ~0.25 GHz. coupling strength to the Kittel mode in a 1.5 mm. diameter YIG sphere. We then conduct surface impedance and two-tone spectroscopy studies on uranium based spin triplet candidate superconductors to investigate cooper-pair spin wave modes over a wide range of frequency, temperature, and applied magnetic field.