Universal time delays in the inelastic core level photoemission of metals

Proposing a theoretical model of the core level photoemission of metals, we investigate the plasmon-driven inelastic photoemission delays based on a nonperturbative treatment of many-electron responses due to the long-range Coulomb potential. Being irrelevant to the plasmon coupling strength as well as the plasmon frequency, the emission delays Δτn of the nth-order plasmon satellites (n=1,2,3,...) are found to be universal order by order among the metals in the core level photoemission where the recoil-less approximation would be valid. In particular, for a main line with its weight e-γ, where γ quantifies the plasmon coupling strength, the average inelastic photoemission delay (Δτ) is found to be γ(1-e-γ)-1Δτ1 and thus is simply scaled by a universal time delay Δτ1. This finding is sharply contrasted with the emission delays under the localized potential, which indicates a fundamental difference in the emission process between extended and localized screenings.