Spin pumping in 𝑑-wave superconductor-ferromagnet hybrids

Abstract

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 Y⁢Ba2⁢Cu3⁢O7−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 Ni80⁢Fe20 (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.