What is the signature of a trion in ARPES?

Recent advances in time-resolved angle-resolved photoemission spectroscopy (TR-ARPES) allow for the possibility of probing multiparticle excited-states in reciprocal space. While neutral two-particle excitations (excitons) have been observed in TR-ARPES, signatures of trions—three-quasiparticle bound states—have only been probed from optical spectroscopy. In this presentation, we demonstrate a generic theory for TR-ARPES in the incoherent regime and apply it to trions in a model of a monolayer transition metal dichalcogenide (TMD). We simulate the ARPES signatures of both positively and negatively charged trions and show that the interaction of the residue holes or electron and hole lead to red shifts or blue shifts, respectively, on the order of the exciton binding energy, compared to the exciton signal. Furthermore, in ARPES detection of positive trions, the additional momentum degree of freedom of the residue particles places a soft lower-bound on the photoemission energy, leading to distinctive asymmetric spectral features, while ARPES detection of negative trions is a potential way to directly observe the exciton spectrum.