Growth optimization of TaN for superconducting spintronics

We have optimized the growth of superconducting TaN thin films on SiO₂ substrates via dc magnetron sputtering and extract a maximum superconducting transition temperature of T_c =5 K as well as a maximum critical field μ₀H_c2 =(13.8 ± 0.1) T. This material is of interest for both different fields of quantum technology and superconducting spintronics as it represents a magnetic field-robust superconductor with strong spin–orbit interaction (SOI). After presenting the results of the growth optimization, we investigate in the second part the impact of the strong SOI in TaN on superconductor/ferromagnet heterostructures. To this end, we analyze the magnetization dynamics of both normal state and superconducting TaN/Ni₈₀Fe₂₀ (permalloy, Py)-bilayers as a function of temperature using broadband ferromagnetic resonance spectroscopy. In particular, we quantify the inverse current-induced torques of the bilayers and compare these results to NbN/Py-bilayers. In the normal state of TaN, we detect a positive damping-like current-induced torque σ_d from the inverse spin Hall effect and a small field-like torque σ_f attributed to the inverse Rashba–Edelstein effect at the TaN/Py-interface. In the superconducting state of TaN, we detect a negative σ_d attributed to the quasiparticle mediated inverse spin Hall effect (QMiSHE) and the unexpected manifestation of a large positive field-like σ_f of unknown origin matching our previous results for NbN/Py-bilayers. The QMiSHE can be used to probe spin currents in emergent quantum materials.