Helium Physisorbed on Metal Surfaces and Thorium Layers on Silver: Zero-Point Motion and Screening Effects in Photoemission and Photoexcitation
DIPC Seminars
- Speaker
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Peter Feulner, Dep. Physics, Technical University of Munich
- When
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2019/04/03
14:00 - Place
- Donostia International Physics Center
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Due to its low binding energy and small mass, the amplitude of the zero-point
motion (ZPM) of adsorbed He is large. Photoemission from He monolayers on
different metal surfaces shows splitting of the He1s line periodic in
momentum, which we explain by a combination of ZPM, screening, and
interference of direct and reflected waves.
Photoexcitation spectra of singly and doubly excited states of He bilayers on
metals deviate from their gas phase counterparts due to strong matrix effects.
For one electron excitations these polarization dependent modifications and
ZPM-induced line broadenings have been analyzed by theory [1]; for the doubly
excited states of the He bilayer - for He gas these excitations are regarded
as archetypical for electron correlation [2] - theory still does not exist.
Experiments show an interesting ZPM-induced correlation of the excitation
energy and the kinetic energy of ions that are created upon excitation decay.
Photoemission from inner-shell levels of thorium metal shows, apart from spin-
orbit splitting, two contributions with slightly different binding energies
that have been explained by screening either through 5f or 6d electrons,
respectively [3]. We show that the ratio of these two contributions can easily
be changed by alloying Th with Ag. In addition, oxidizing the Th layers
suppresses one of the components completely.
We believe that He1s photoemission and the Th/Ag system are interesting
candidates for investigations with attosecond techniques, streaking (Th/Ag)
and RABBITT (He1s): He1s because of the contributions of two different
electron trajectories, and Th/Ag because of its tunable screening dynamics.
[1] S. Kossler, P. Feulner, J.-P. Gauyacq, Phys. Rev. B89, 165410.
[2] J.W. Cooper, U. Fano, F. Prats, Phys. Rev. Lett. 10, 518.
[3] J.C. Fuggle et al., Phys. Rev. Lett. 45, 1597.
Host: Daniel Sánchez Portal