Superconductivity provides a giant enhancement to the spin battery effect

Abstract

We develop a theory of the spin battery effect in superconductor/ferromagnetic insulator (SC/FI) systems taking into account the magnetic proximity effect. We demonstrate that the spin-energy mixing enabled by the superconductivity leads to the enhancement of spin accumulation by several orders of magnitude relative to the normal state. This finding can explain the recently observed giant inverse spin Hall effect generated by thermal magnons in the SC/FI system. We suggest a non-local electrical detection scheme which can directly probe the spin accumulation driven by the magnetization dynamics. We predict a giant Seebeck effect converting the magnon temperature bias into the non-local voltage signal. We also show how this can be used to enhance the sensitivity of magnon detection even up to the single-magnon level.

Role of Two-Dimensional Ising Superconductivity in the Nonequilibrium Quasiparticle Spin-to-Charge Conversion Efficiency

“…1B) and thus OOP Cooper pairing is protected and stabilized by the resulting Ising SO-field (76 meV in the monolayer limit) (20,41). In this regime, the YIG-induced IP exchange field (< 1 meV) (14,41) hardly spin-splits the QP DOS of the 2H-NbSe2 and the transition-state enhancement of QP iSHE thus relies mostly on the superconducting-coherence-relevant resonant absorption (14,16,42), (25) and Majorana fermions (26,27). Our findings, together with recent progresses in 2D SCs and magnetic vdW crystals (22,24), open up an avenue for highlyefficient atomically-thin spin-to-charge converters via symmetry engineering.…”

“…This giant transition-state QP iSHE has been qualitatively explained in terms of two competing mechanisms of the superconducting coherence versus the exchange-field-frozen QP relaxation. A very recent theory (16) has pointed out that the electron-hole symmetry breaking present in SC/FMI (FMI = ferromagnetic insulator) bilayers mixes the spin and heat imbalances and can cause the enhancement of QP spin accumulation by several orders of magnitude relative to the normal state. Both these studies (14,15) emphasize the crucial role of the spin-splitting of QP densityof-states (DOS) and the resulting electron-hole asymmetry in enhancing the spin sensitivity of the SC detector (5,15).…”