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

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.