Fig. 5: Mechanisms for spin transport.
From: Optical spin-orbit torque in heavy metal-ferromagnet heterostructures
a The mechanism based on the diffusion of electrons and holes. The optical orientation in Pt induces a spin polarization (blue arrows) on electrons in conduction state (filled circles)/holes in valence state (empty circles). Both electrons and holes diffuse in all directions. The diffusivity (orange arrows) or diffusion length could be different for electrons and holes. \(\varepsilon _{\mathrm{F}}\) and \(\varepsilon _{{\mathrm{vac}}}\) represent the Fermi level and vacuum level, respectively. b The mechanism based on the drift of electrons and holes. An electric field (E-field) develops at the interface with a typical width (w) of ≈1 nm due to the difference in work functions. The sign of E-field is denoted as negative because the work function of Pt is higher than that of Co or Cu. The E-field induces a directional motion of electrons and holes at the interface. The drift velocity (orange arrows), determined by the summation of the group velocity over k-vectors, could be different for electrons and holes.
