Spin-polarized Shapiro steps and spin-precession-assisted multiple Andreev reflection

C. Holmqvist; M. Fogelström; W. Belzig

doi:10.1103/PhysRevB.90.014516

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Spin-polarized Shapiro steps and spin-precession-assisted multiple Andreev reflection

C. Holmqvist, M. Fogelström, W. Belzig

DOI 10.1103/PhysRevB.90.014516 · Physical Review B

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Abstract

We investigate the charge and spin transport of a voltage-biased superconducting point contact coupled to a nanomagnet. The magnetization of the nanomagnet is assumed to precess with the Larmor frequency ωL when exposed to ferromagnetic resonance conditions. The Larmor precession locally breaks the spin-rotation symmetry of the quasiparticle scattering and generates spin-polarized Shapiro steps for commensurate Josephson and Larmor frequencies that lead to magnetization reversal. This interplay between the ac Josephson current and the magnetization dynamics occurs at voltages |V|=ℏωL/2en for n=1,2,..., and the subharmonic steps with n>1 are a consequence of multiple Andreev reflection (MAR). Moreover, the spin-precession-assisted MAR generates quasiparticle scattering amplitudes that, due to interference, lead to current-voltage characteristics of the dc charge and spin currents with subharmonic gap structures displaying an even-odd effect.