Photo-Spin-Voltaic Effect

This presentation reports that a spin voltage can be created by photons in a non-magnetic metal that is in close proximity to a magnetic insulator.1 This phenomenon is referred to as the photo-spin-voltaic (PSV) effect, in light of its analogy to the conventional photo-voltaic effect. The effect offers a completely new method for generation of pure spin currents, as an alternative to the well-established spin pumping, spin Hall, and spin Seebeck effects.The experiments used normal metal/magnetic insulator bi-layered structures where the normal metal (NM) was a nm-thick Pt, Pd, or Cr layer and the magnetic insulator (MI) was an Y3Fe5O12, doped Y3Fe5O12, or BaFe12O19 film with a thickness in the 10-105 nm range. When light illuminates the NM layer, photons induce a spin voltage near the NM/MI interface and a corresponding pure spin current across the NM thickness. Such a spin current can produce a measurable electric voltage in the NM film via the inverse spin Hall effect. Measurements using various control samples, light sources, and optical filters revealed the magnetic and optical nature of the PSV effect and clearly excluded any thermal origin. The physical mechanism of the PSV effect can be interpreted as follows. When light illuminates the NM film, photons with appropriate energy excite electrons in the occupied bands to the unoccupied bands. For the NM atomic layers in close proximity to the MI, the efficiency of the photon-driven electron excitation is different for electrons in different spin channels. This efficiency difference, together with the difference in the diffusion of the excited electrons and holes, gives rise to an effective spin voltage near the interface. This interpretation was supported by comparisons between the theoretical expectations and the experimental observations.[1] “Photo-spin-voltaic effect,” David Ellsworth, Lei Lu, Jin Lan, Houchen Chang, Peng Li, Zhe Wang, Jun Hu, Bryan Johnson, Yuqi Bian, Jiang Xiao, Ruqian Wu, and Mingzhong Wu, Nature Phys., doi:10.1038/nphys3738 (2016).