Photoemission from solid targets includes the excitation and motion of electrons inside the substrate, followed
by their propagation in vacuum and detection. It thus depends on the electronic band structure of the solid
in the two distinct spectral domains of bound initial and continuum final states. While the imprint of the
static (initial-state) valence electronic structure of solids on photoemission spectra is routinely examined
in standard photoemission spectroscopy in the energy domain, state-of-the-art time-resolved photoelectron
spectroscopy allows, in addition, the scrutiny of photoelectron propagation in the electronic continuum. Within
a quantum-mechanical model for attosecond time-resolved interferometric photoelectron emission from solids,
we calculated photoemission spectra as a function of the delay between the exciting primary attosecond pulse
train and assisting infrared (IR) laser pulse. Accounting for final-state interactions of the photoelectron with the
IR laser electric field and the periodic substrate, our numerical results for interferometric photoemission from the
3d-valence band of Cu(111) surfaces show a striking resonantly enhanced sideband yield at photoelectron kinetic
energies near 24 eV, in conjunction with a pronounced increase of the photoelectron wave-function amplitude
inside the solid on a length scale of a few nanometers. This resonant shift of final-state photoelectron-probability
density towards the bulk can be interpreted as an increase in the photoelectron propagation time in the solid and
is commensurate with the resonantly enhanced spectral sideband-phase shifts observed in recent two-pathway
two-photon interference spectra by Kasmi et al. [Optica 4, 1492 (2017)].
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Distinction of Electron Dispersion in Time-Resolved Photoemission Spectroscopy
While recent experiments provided compelling evidence for an intricate dependence of attosecond photoemission-time delays on the solid’s electronic band structure, the extent to which electronic transport and dispersion in solids can be imaged in time-resolved photoelectron (PE) spectra remains poorly
understood. Emphasizing the distinction between photoemission time delays measured with two-photon, two-color interferometric spectroscopy, and transport times, we demonstrate how the effect of energy dispersion in the solid on photoemission delays can, in principle, be observed in interferometric
photoemission. We reveal analytically a scaling relation between the PE transport time in the solid and the observable photoemission delay and confirm this relation in numerical simulations for a model system. We trace photoemission delays to the phase difference the PE accumulates inside the solid and, in particular, predict negative photoemission delays. Based on these findings, we suggest a novel time-domain interferometric solid-state energy-momentum-dispersion imaging method.
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- Award ID(s):
- 1802085
- NSF-PAR ID:
- 10275423
- Date Published:
- Journal Name:
- Physical review letters
- Volume:
- 125
- ISSN:
- 1092-0145
- Page Range / eLocation ID:
- 043201
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1103/PhysRevLett.125.043201
