Role of matrix elements in the time-resolved photoemission signal

Time- and angle-resolved photoemission spectroscopy (TR-ARPES) provides access to the ultrafast evolution of electrons and many-body interactions in solid-state systems. However, the momentum- and energy-resolved transient photoemission intensity may not be unambiguously described by the intrinsic relaxation dynamics of photoexcited electrons alone. The interpretation of the time-dependent photoemission signal can be affected by the transient evolution of the electronic distribution, and both the one-electron removal spectral function as well as the photoemission matrix elements. Here we investigate the topological insulator Bi1.1Sb0.9Te2S to demonstrate, by means of a detailed probe-polarization dependent study, the transient contribution of matrix elements to TR-ARPES.