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The Center for Bright Beams, A National Science Foundation Science and Technology Center

Theory of Transverse Energy Distribution of Photoelectrons

Ab Initio Many-body Photoemission Theory of Transverse Energy Distribution of Photoelectrons: PbTe(111) as a Case Study with Experimental Comparisons

J. K. Nangoi, S. Karkare, R. Sundararaman, H. A. Padmore, and T. A. Arias

Previous works predict that the (111) surface of PbTe is capable of producing high-brightness photoelectron beam with very low mean transverse energy (MTE) ≤ 15 meV. However, our experiments yield photoelectron beams with MTE values that are up to twenty times higher. Our experiments also show lower photoemission threshold than predicted. To explain these mysteries, we develop a new ab Initio many-body photoemission theory to calculate the MTE of photoemitted electrons. Using this theory, our calculations reproduce both the magnitude of the MTE from our measurements on PbTe(111) and the observed photoemission below the predicted threshold. Our results show that excited bulk electronic states and coherent electron-photon-phonon scattering, both of which the previous works ignore, play significant roles in photoemission from PbTe(111).

Figure: Top: Ab initio many-body bulk photoemission process: direct-only photoemission (left), which involves electron-photon scattering, and phonon-mediated photoemission (right), which involves coherent electron-photon-phonon scattering. Bottom: Mean transverse energy (MTE) of photoelectrons emitted from PbTe(111) as a function of laser photon energy: previous prediction by other authors (thick curve with small MTE values ≤ 15 meV), our experiments (points with error bars), our calculations without phonon effects (dashed curve) and the associated threshold (vertical dashed line), and our calculations with phonon effects (solid curve). Compared to the previous prediction, our calculations are in far better agreement with our experiments.

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