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Evidence for Umklapp electron scattering emission from metal photocathodes

I-J. Shan, L. A. Angeloni, and W. Andreas Schroeder*

  • *Contact author: andreas@uic.edu
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APS Open Sci. 1, 000171 – Published 13 October, 2026

DOI: https://doi.org/10.1103/1c1y-fzsj

Abstract

Comparison of the measured spectral emission properties of single-crystal Cu(001) and W(111) photocathodes to established photoemission theories reveals evidence for an additional one-photon emission process predominantly affecting electron emission near and below the photoemission threshold. This additional photoemission process is postulated to be due to a momentum-resonant Franck-Condon mechanism mediated by inelastic Umklapp electron scattering. An initial first-principles simulation of this emission process (involving the electron thermal effective mass, the inelastic electron mean free path at the vacuum level, and the number of Fermi surfaces in the metal), when combined with a direct one-step band emission model, is consistent with the measured spectral dependencies of both the quantum efficiency and mean transverse energy of electron photoemission from the two single-crystal metal photocathodes.

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APS Open Sci. 1, 000171– Published 13 October, 2026
Vol. 1
  • Received 9 June 2026
  • Accepted 26 August 2026
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