Magneto-Optical Detection of the Orbital Hall Effect in Chromium

The orbital Hall effect has been theoretically predicted but its direct observation is a challenge. Here, we report the magneto-optical detection of current-induced orbital accumulation at the surface of a light 3$d$ transition metal, Cr. The orbital polarization is in-plane, transverse to the current direction, and scales linearly with current density, consistent with the orbital Hall effect. Comparing the thickness-dependent magneto-optical measurements with $\mathit{\text{ab}}\mathit{\text{initio}}$ calculations, we estimate an orbital diffusion length in Cr of $6.6\pm 0.6$ nm.