Abstract
In superconductors spin-split by an exchange field, thermal effects are coupled to spin transport. We show how an oscillating electromagnetic field in such systems creates spin imbalance, that can be detected with a spin-polarized probe. The sign and magnitude of the probe signal result from a competition between processes converting field induced spin energy imbalance to spin imbalance, dominant at low frequencies, and microwave-driven pair breaking at high frequencies. In the presence of spin-flip scattering, we show that ac excitation also leads to multistabilities in the superconducting state.
Highlights
Long-lived spin excitations are interesting for spintronics applications, and the spin transport in superconductors has recently attracted renewed attention in this context [1,2,3]
We show how an oscillating electromagnetic field in such systems creates spin imbalance, that can be detected with a spin-polarized probe
We find that the ac driving generates spin imbalance that is either parallel or antiparallel to the exchange field, depending on the drive frequency
Summary
Long-lived spin excitations are interesting for spintronics applications, and the spin transport in superconductors has recently attracted renewed attention in this context [1,2,3]. A second approach for spin injection studied in a number of recent experiments [4,5,6,7,8,9] is to use a magnetic field or proximity to ferromagnetic insulators to Zeeman split the density of states of the superconductor [10,11] (cf Fig. 1), so that injection of current from an unpolarized probe generates observable spin accumulation. Based on the above discussion, a photo-spin-electric effect should be present in spin-split superconductors— the absorbed radiation generates spin imbalance, which relaxes slowly via inelastic scattering. This is interesting to consider, e.g., in the context of measurements that use microwave signals to probe spin resonances of the quasiparticles [9].
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