At interfaces with inversion symmetry breaking, the Rashba effect couples the motion of the electrons to their spin; as a result, a spin charge interconversion mechanism can occur. These interconversion mechanisms commonly exploit Rashba spin splitting at the Fermi level by spin pumping or spin torque ferromagnetic resonance. Here, we report evidence of significant photoinduced spin-to-charge conversion via Rashba spin splitting in an unoccupied state above the Fermi level at the $\mathrm{Cu}(111)/\alpha \text{−}{\mathrm{Bi}}_2{\mathrm{O}}_3$ interface. We predict an average Rashba coefficient of $1.72\times {10}^{-10}\mathrm{eV}\mathrm{m}$ at 1.98 eV above the Fermi level, by a fully relativistic first principles analysis of the interfacial electronic structure with spin orbit interaction. We find agreement with our observation of helicity dependent photoinduced spin-to-charge conversion excited at 1.96 eV at room temperature, with a spin current generation of $J_s={10}^6\mathrm{A}/{\mathrm{m}}^2$. The present Letter shows evidence of efficient spin charge conversion exploiting Rashba spin splitting at excited states, harvesting light energy without magnetic materials or external magnetic fields.

• Received 17 January 2019
• Revised 3 April 2019

DOI:https://doi.org/10.1103/PhysRevLett.122.256401