Towards robust dichroism in angle-resolved photoemission

Dichroic techniques are highly relevant in the field of topological materials, layered systems, and spin-polarized electronic states. Dichroism in angle-resolved photoemission is per se a matrix element effect, which depends on the initial and final states as well as on the perturbation by the light field. Although matrix element effects in ARPES such as dichroism are important for addressing properties of the initial state wave functions, the results can strongly depend on experimental geometry or final state effects. Combining experimental data on bulk WSe2 taken at soft x-ray photon energies with state-of-the-art photoemission calculations, we demonstrate that a dichroic observable called time-reversal dichroism remains unaffected against variation of photon energy, light polarization, and the angle of incidence. We demonstrate a direct link of TRDAD obtained with both linearly and circularly polarized photons to the initial state properties indicating its broad applicability. The robustness of this matrix element effect indicates a considerable benefit over other dichroic techniques and encourages further experimental and theoretical investigations. Matrix element effects in ARPES are important for addressing properties of the initial state wave functions, but the results can strongly vary with experimental configuration or final state. The authors show that an observable called time-reversal dichroism can filter out such effects, providing a direct link to orbital angular momentum and pseudospin.