Impact of a photoemission resonance on the measured transition timescale in solid state photoemission

Fundamental quantum transition timescales are accessible through the spin polarization of photoelectrons coming from initially spin-degenerate states for solid-state materials. In this work we investigate the modification of this timescale in the vicinity of a resonance in photoemission from a solid. We employ spin- and angle-resolved photoemission spectroscopy (SARPES) to study the valence band of 1T-TiSe2 and 1T-TiTe2, with an excitation photon energy coinciding with the Ti 3p-3d autoionization state. The energy derivative of the measured spin polarization, which is in the off-resonance case proportional to the transition time, reveals a sign reversal and significant magnitude decrease compared to off-resonance measurements. We show that this effect goes beyond the conventional semianalytical models used to translate spin polarization to the transition time delay. At the photoemission resonance, the underlying interference assumption of the model breaks down, and additional information about resonance strength is needed to extract the transition time delays.