By performing angle-resolved photoemission spectroscopy (ARPES) and state-of-the-art SPR-KKR photoemission calculations on the paradigmatic Weyl semimetals Ta(As,P) [1] we show the spectroscopic manifestation of topological features and Weyl physics beyond the simple photointensity over a broad range of excitation energies from the vacuum ultraviolet to the soft X-Ray regime and compare the surface to the bulk band structure [2]. We further show the drawbacks of the existing spectroscopic techniques used to determine whether the given material has non-zero Chern number and discuss an improved approach for identifying Fermi arcs using differential ARPES measurements, their relation to orbital angular momentum (OAM) as well as the proper final state description. Consequently, we conclude that a more realistic description of the final state is needed to explain dichroism by modeling the photoemission matrix element.

Next, we will discuss dichroic techniques highly relevant in topological materials, layered systems, and spin-polarized electronic states [2-4]. Dichroism in angle-resolved photoemission is per se a matrix element effect, which depends on the initial and final states and the light field's perturbation. 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 (TRDAD) remains unaffected against variation of photon energy, light polarization, and the angle of incidence [5]. The robustness of this matrix element effect indicates a considerable benefit over other dichroic techniques.

[1] Ünzelmann, M. et al., Nat Commun 12, 3650 (2021)
[2] Schusser, J. et al., Physical Review Letters 129 (24), 246404
[3] Beaulieu, S. et al., Physical Review Letters 125 (21), 216404
[4] Beaulieu, S. et al., npj quantum materials 6 (1), 93
[5] Schusser, J. et al., Communications Physics 7, 270 (2024)