LAUSR

We detected and analyzed a spin-dependent intensity asymmetry for spin-degenerate surface states at the $\overline{\mathrm{M}}$ point in the unoccupied electronic structure of Tl/Ge(111). Approximating the initial state by a plane wave, we calculated the inverse-photoemission process and obtained good agreement with the experimental data. Our model reveals that this spin asymmetry at a point of time-reversal invariant momentum (TRIM) is of different origin than other effects discussed in the literature, which are based on the light detection geometry, photon energy, and experimental probing depth of the electrons. Instead, the spin asymmetry in this nonmagnetic material with spin-orbit interaction is caused by breaking the initial-state time-reversal symmetry in the experiment. The effect is of general nature and can occur in spin- and angle-resolved inverse photoemission as well as photoemission at TRIM points.