Imaging Momentum–Space Two‐Particle Correlations at Surfaces

Abstract

Photoelectron and electron energy loss spectroscopies have been highly instrumental in revealing the various facets of electronic properties of materials. For a direct insight into two‐particle correlations, a technique is needed that resolves two emitted electrons in coincidence. Herein, an overview on the experimental realization of correlation spectroscopy and the interpretation of the recorded spectra from theory is provided. The relation of the measured spectra to the details of the spin‐, energy‐ and wavevector‐resolved electron–electron interactions is focused upon. To disentangle the contributions of exchange from the charge‐density correlation, positrons instead of electrons are used as projectiles. The short intrinsic time of the Auger decay and the neutralization of ions near a surface are used to estimate the characteristic timescale for the correlated electron dynamics in metals to be 40–400 attoseconds. The potential of conducting double photoemission studies with pulsed laser‐based light sources is addressed.

Time-of-flight photoelectron momentum microscopy with 80–500 MHz photon sources: electron-optical pulse picker or bandpass pre-filter

“…As a scientific outlook, we address the technique of momentum mapping of electron pairs that are detected in coincidence. This 2e spectroscopy provides a direct insight into two-particle correlations; for an excellent overview, see the recent review by Schumann et al (2020). Two classes of processes have been studied -double photoelectron emission (h, 2e) and pair emission after fast electron impact (e, 2e).…”