  Gate-induced modulation of the spin-orbit interaction (SOI) in a 1.5 nm-thick
Pd thin film grown on a ferrimagnetic insulator was investigated. Efficient
charge accumulation by ionic gating enables a substantial upshift in the Fermi
level of the Pd film, which was corroborated by suppression of the resistivity
in the Pd. Electromotive forces arising from the inverse spin Hall effect in Pd
under spin pumping were substantially modulated by the gating, in consequence
of the modulation of the spin Hall conductivity of Pd as in an ultrathin Pt
film. The same experiment using a thin Cu film, for which the band structure is
largely different from Pd and Pt and its SOI is quite small, provides further
results supporting our claim. The results obtained help in developing a
holistic understanding of the gate-tunable SOI in solids and confirm a previous
explanation of the significant modulation of the spin Hall conductivity in an
ultrathin Pt film by gating.
