Magnitude of the orbital Hall effect and orbital torques
In plain words
Theory predicts that currents in light metals such as titanium push electron orbital angular momentum sideways, called the orbital Hall effect, and that this can twist nearby magnets. Experiments have detected it, but measured sizes and theoretical values disagree and are hard to separate from spin effects.
Precise statement
Tight-binding and first-principles theory predict orbital Hall conductivities in Ti, V, Cr and Cu exceeding the spin Hall conductivity of Pt. Magneto-optical Kerr detection in Ti and Cr (2023) and orbital-torque measurements in light-metal/ferromagnet bilayers report effects of varying size. Determine the orbital Hall conductivity and orbital diffusion length in Ti and Cr from a measurement that separates orbital from spin accumulation, and reconcile them with theory including the ambiguity in defining the orbital current operator. An answer is values with error bars and the ratio to theory.
What would settle it
Thickness-dependent orbital accumulation and torque measured in several light metals with independent calibration, compared with first-principles values computed with a stated orbital current definition.
Status in the literature
Kerr-effect observations in Ti and Cr were reported in 2023; magnitudes and orbital diffusion lengths remain disputed.