Spin polarization and attosecond time delay in photoemission from spin degenerate states of solids

TL;DR

This paper investigates the relationship between spin polarization and attosecond time delays in photoemission from spin degenerate states of solids, combining a semi-quantitative model with experimental SARPES measurements.

Contribution

It introduces a semi-quantitative model linking spin and time scales in photoemission and provides the first experimental measurement of time delay in a dispersive band.

Findings

Time delay exceeds 26 attoseconds in Cu(111) electrons.

Spin polarization is related to phase shifts in photoemission.

Model enhances understanding of spin- and angle-resolved photoemission spectroscopy.

Abstract

After photon absorption, electrons from a dispersive band of a solid require a finite time in the photoemission process before being photoemitted as free particles, in line with recent attosecondresolved photoemission experiments. According to the Eisenbud-Wigner-Smith model, the time delay is due to a phase shift of different transitions that occur in the process. Such a phase shift is also at the origin of the angular dependent spin polarization of the photoelectron beam, observable in spin degenerate systems without angular momentum transfer by the incident photon. We propose a semi-quantitative model which permits to relate spin and time scales in photoemission from condensed matter targets and to better understand spin- and angle-resolved photoemission spectroscopy (SARPES) experiments on spin degenerate systems. We also present the first experimental determination by SARPES of this time delay in a dispersive band, which is found to be greater than 26 as for electrons emitted from the sp-bulk band of the model system Cu(111).