A theory of photoelectron escape time $\tau$ from crystals is presented that combines the one-step photoemission theory with the Wigner delay. Equations are formally derived and illustrated with an exactly solvable model. An ab initio implementation with the augmented-plane-wave-based scattering method is applied to emission from Mg(0001). The theory is in reasonable agreement with streaking measurements. Lattice scattering is found to cause rapid variations of $\tau$ with photon energy both for the valence band and for the $2p$ core band emission, and a strong dependence on the initial state is revealed.

• Received 7 May 2020
• Revised 17 July 2020
• Accepted 17 August 2020

DOI:https://doi.org/10.1103/PhysRevB.102.115116