One-step theory of photoelectron escape time: Attosecond spectroscopy of Mg(0001)

A theory of photoelectron escape time τ 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 τ 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.