Growth optimization of TaN for superconducting spintronics

Abstract

Abstract 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 μ 0 H 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.