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Søren Ulstrup

Ramifications of optical pumping on the interpretation of time-resolved photoemission experiments on graphene

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  • Søren Ulstrup
  • Jens Christian Johannsen, École Polytechnique Fédérale de Lausanne
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  • Federico Cilento, Elettra Sincrotrone Trieste SCpA
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  • Alberto Crepaldi, Elettra Sincrotrone Trieste SCpA
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  • Jill A. Miwa
  • Michele Zacchigna, CNR IOM Lab TASC
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  • Cephise Cacho, STFC Rutherford Appleton Lab, STFC Rutherford Appleton Laboratory, Cent Laser Facil
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  • Richard T. Chapman, STFC Rutherford Appleton Lab, STFC Rutherford Appleton Laboratory, Cent Laser Facil
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  • Emma Springate, STFC Rutherford Appleton Lab, STFC Rutherford Appleton Laboratory, Cent Laser Facil
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  • Felix Fromm, Tech Univ Chemnitz, Technische Universitat Chemnitz, Inst Phys
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  • Christian Raidel, Tech Univ Chemnitz, Technische Universitat Chemnitz, Inst Phys
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  • Thomas Seyller, Tech Univ Chemnitz, Technische Universitat Chemnitz, Inst Phys
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  • Phil D. C. King, Univ St Andrews, University of St Andrews, SUPA, Sch Phys & Astron
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  • Fulvio Parmigiani, Univ Cologne, University of Cologne, Int Fac
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  • Marco Grioni, École Polytechnique Fédérale de Lausanne
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  • Philip Hofmann

In pump-probe time and angle-resolved photoemission spectroscopy (TR-ARPES) experiments the presence of the pump pulse adds a new level of complexity to the photoemission process in comparison to conventional ARPES. This is evidenced by pump-induced vacuum space-charge effects and surface photovoltages, as well as multiple pump excitations due to internal reflections in the sample-substrate system. These processes can severely affect a correct interpretation of the data by masking the out-of-equilibrium electron dynamics intrinsic to the sample. In this study, we show that such effects indeed influence TR-ARPES data of graphene on a silicon carbide (SiC) substrate. In particular, we find a time- and laser fluence-dependent spectral shift and broadening of the acquired spectra, and unambiguously show the presence of a double pump excitation. The dynamics of these effects is slower than the electron dynamics in the graphene sample, thereby permitting us to deconvolve the signals in the time domain. Our results demonstrate that complex pump-related processes should always be considered in the experimental setup and data analysis. (C) 2015 Elsevier B.V. All rights reserved.

Original languageEnglish
JournalJournal of Electron Spectroscopy and Related Phenomena
Volume200
Pages (from-to)340-346
Number of pages7
ISSN0368-2048
DOIs
Publication statusPublished - Apr 2015

    Research areas

  • Graphene, Time- and angle-resolved photoemission, Space charge, Hot electrons, CARRIER MULTIPLICATION, SPECTROSCOPY, SURFACE

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