Dichroism in the ultrafast ARPES response and valence band orbital nature of BaNiS₂

Time-resolved ARPES gives access to the band structure and ultrafast dynamics of excited electronic states in solids. The orbital character of the bands close to the Fermi level is essential to understand the origin of several exotic phenomena in quantum materials. By performing polarization-dependent time-and angle-resolved photoemission spectroscopy and by analyzing the photoelectron yield for two different crystal orientations, we identify the orbital character of bands below and above the chemical potential for the Dirac semimetal BaNiS2. Our results illustrate how the control and understanding of matrix elements' effects in time-resolved photoemission spectroscopy can be a powerful tool for the study of quantum materials.