Role of matrix elements in the time-resolved photoemission signal

TL;DR

This paper investigates how transient photoemission matrix elements influence the interpretation of time-resolved photoemission spectroscopy data, using a polarization study on a topological insulator to clarify their role.

Contribution

It demonstrates the significant impact of matrix element evolution on photoemission signals, highlighting the need to consider these effects in ultrafast spectroscopy analysis.

Findings

Matrix elements significantly affect the time-resolved photoemission signal.

Polarization-dependent measurements reveal transient matrix element contributions.

Proper interpretation of ultrafast dynamics requires accounting for matrix element evolution.

Abstract

Time- and angle-resolved photoemission spectroscopy accesses the ultrafast evolution of quasiparticles and many-body interactions in solid-state systems. However, the momentum- and energy-resolved transient photoemission intensity may not be unambiguously related to the intrinsic relaxation dynamics of photoexcited electrons. In fact, interpretation of the time-dependent photoemission signal can be affected by the transient evolution of both the one-electron removal spectral function as well as the photoemission dipole matrix elements. Here we investigate the topological insulator Bi$_{1.1}$Sb$_{0.9}$Te$_2$S to demonstrate, by means of a careful probe-polarization study, the transient contribution of matrix elements to the time-resolved photoemission signal.