Spin pumping in d -wave superconductor-ferromagnet hybrids

Spin pumping across ferromagnet/superconductor (F/S) interfaces has attracted much attention lately, yet the focus has been mainly on $s$-wave superconductor based systems whereas (high-temperature) $d$-wave superconductors such as $\mathrm{Y}{\mathrm{Ba}}₂{\mathrm{Cu}}₃{\mathrm{O}}_{7\text{\ensuremath{-}}\mathrm{d}}$ (YBCO) have received scarce attention despite their fundamental and technological interest. Here we use wideband ferromagnetic resonance to study spin-pumping effects in bilayers that combine a soft metallic ${\mathrm{Ni}}₈₀{\mathrm{Fe}}₂₀$ (Py) ferromagnet and YBCO. We evaluate the spin conductance in YBCO by analyzing the magnetization dynamics in Py. We find that the Gilbert damping exhibits a drastic drop as the heterostructures are cooled across the normal-superconducting transition and then, depending on the S/F interface morphology, either stays constant or shows a strong upturn. This unique behavior is explained considering quasiparticle density of states at the YBCO surface, and is a direct consequence of zero-gap nodes for particular directions in the momentum space. Besides showing the fingerprint of $d$-wave superconductivity in spin pumping, our results demonstrate the potential of high-temperature superconductors for fine tuning of the magnetization dynamics in ferromagnets using $k$-space degrees of freedom of $d$-wave/F interfaces.