Quasiparticle spin-to-charge conversion in superconductors detected by nonlocal magnon spin transport*

Injection and excitation of electrons, typically called Bogoliubov quasiparticles (QPs), in a superconductor (SC) with either external (Zeeman) or internal (exchange) spin-splitting field under non-equilibrium conditions (i.e. voltage bias or temperature gradient) have been one of the central research topics in superconducting spintronics. This is because their exotic transport properties, derived from the superconductivity-facilitated coupling between different non-equilibrium imbalances (e.g. spin, charge, heat and spin-heat), can considerably improve the functionality and performance of spintronic devices. 

      In the first part of my talk, I would describe our recent magnon spin-transport experiment [1] that the conversion efficiency of thermal-magnon spin to QP charge via an inverse spin-Hall effect (iSHE) in an exchange-spin-split Nb layer can be significantly enhanced by up to 3 orders of magnitude in the normal-to-superconducting transition regime. I will semi-quantitatively explain this giant transition-state QP iSHE in terms of two competing mechanisms of the superconducting coherence versus the exchange-field-frozen QP relaxation. 

     In the second part, I would describe how out-of-plane (OOP) Cooper pairing of two-dimensional (2D) Ising superconductivity influences the transition-state enhancement of QP iSHE in a superconducting flake of 2H-NbSe₂ and compare its enhancement magnitude with a conventional superconducting thin film of Nb (BCS SC) [2]. We expect that along with recent advances in 2D SCs of various intriguing properties (e.g. type-I/-II Ising, Rashba, topological SCs), our study would help find right material combinations for developing superconducting spintronic devices over conventional BCS SCs.