One-step theory of pump-probe photoemission

TL;DR

This paper introduces a comprehensive theoretical framework for pump-probe photoemission using the Keldysh formalism, enabling quantitative analysis of time-dependent photocurrents in simple metals with relativistic effects.

Contribution

It presents a one-step, real-time theoretical approach to pump-probe photoemission based on the Keldysh formalism, closely related to Pendry's formulation.

Findings

Quantitative calculation of time-dependent photocurrent in simple metals

Inclusion of relativistic effects as a function of pump-probe delay

Applicable to valence- and core-electron excitations

Abstract

A theoretical frame for pump-probe photoemission is presented. The approach is based on a general formulation using the Keldysh formalism for the lesser Green's function to describe the real-time evolution of the electronic degrees of freedom in the initial state after a strong pump pulse that drives the system out of equilibrium. The final state is represented by a time-reversed low-energy electron diffraction state. Our one-step description is related to Pendry's original formulation of the photoemission process as close as possible. The formalism allows for a quantitative calculation of time-dependent photocurrent for simple metals where a picture of effectively independent electrons is assumed as reliable. The theory is worked out for valence- and core-electron excitations. It comprises the study of different relativistic effects as a function of the pump-probe delay.