Ramifications of optical pumping on the interpretation of time-resolved photoemission experiments on graphene
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Abstract 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.
Ulstrup , S , Johannsen , J C , Cilento , F , Crepaldi , A , Miwa , J A , Zacchigna , M , Cacho , C , Chapman , R T , Springate , E , Fromm , F , Raidel , C , Seyller , T , King , P D C , Parmigiani , F , Grioni , M & Hofmann , P 2015 , ' Ramifications of optical pumping on the interpretation of time-resolved photoemission experiments on graphene ' Journal of Electron Spectroscopy and Related Phenomena , vol 200 , pp. 340–346 . DOI: 10.1016/j.elspec.2015.04.010
Journal of Electron Spectroscopy and Related Phenomena
Copyright © 2015 Published by Elsevier B.V. This is the author’s version of a work that was accepted for publication in Journal of Electron Spectroscopy and Related Phenomena. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Electron Spectroscopy and Related Phenomena, DOI: https://dx.doi.org/10.1016/j.elspec.2015.04.010
The authors acknowledge financial support from the VILLUM foundation, The Danish Council for Independent Research / Technology and Production Sciences, the Swiss National Science Foundation (NSF), EPSRC, The Royal Society and the Italian Ministry of University and Research (Grants No. FIRBRBAP045JF2 and No. FIRB-RBAP06AWK3). Access to the Artemis Facility was funded by STFC. Work in Chemnitz was supported by the European Union through the project ConceptGraphene, and by the German Research Foundation in the framework of the SPP 1459 Graphene.
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