Wavelength-dependence of the spin-orbit optical properties of Au

Spin-orbit coupling affects the interaction of a metal’s electrons with electromagnetic fields and gives rise to transport phenomena such as the spin Hall effect and the inverse Faraday effect. To date, most experimental research into spin-orbit transport properties in non-magnetic metals has focused on the response to DC electric fields. Here, we report the results of experimental measurements of spin-orbit properties of Au at optical frequencies. We perform time-resolved Magneto optic Kerr effect (TR-MOKE) measurements on Au/Co heterostructures. Ultrafast optical excitation of the cobalt layer drives spin accumulation into an adjacent Au layer that is ~200 nm thick. The spin accumulation, together with spin-orbit coupling, leads to non-zero terms in the off-diagonal conductivity tensor. To measure these off-diagonal terms, we measure the polar MOKE of the Au as a function of wavelength. Our experimental data for wavelengths between 380 and 1030 nm are in agreement with density-functional theory predictions.