Ultrafast electronic linewidth broadening in the C <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>1</mml:mn><mml:mi>s</mml:mi></mml:mrow></mml:math> core level of graphene
Davide Curcio, Sahar Pakdel, Klara Volckaert, Jill A. Miwa, Søren Ulstrup, Nicola Lanatà, Marco Bianchi, Dmytro Kutnyakhov, Federico Pressacco, Günter Brenner, Siarhei Dziarzhytski, H. Redlin, Steinn Ýmir Ágústsson, K. Medjanik, D. Vasilyev, H. J. Elmers, G. Schönhense, Christian Tusche, Ying‐Jiun Chen, Florian Speck, Thomas Seyller, Kevin Bühlmann, Rafael Gort, Florian Diekmann, Kai Roßnagel, Yves Acremann, J. Demšar, W. Würth, Daniel Lizzit, Luca Bignardi, Paolo Lacovig, Silvano Lizzit, Charlotte E. Sanders, Philip Hofmann
Abstract
We show that the presence of a transiently excited hot electron gas in graphene leads to a substantial broadening of the C $1s$ line probed by time-resolved x-ray photoemission spectroscopy. The broadening is found to be caused by an exchange of energy and momentum between the photoemitted core electron and the hot electron gas, rather than by vibrational excitations. This interpretation is supported by a quantitative line-shape analysis that accounts for the presence of the excited electrons. Fitting the spectra to this model directly yields the electronic temperature of the system, in good agreement with electronic temperature values obtained from valence band data. Furthermore, we show how the momentum change of the outgoing core electrons leads to a detectable but very small change in the time-resolved photoelectron diffraction pattern and to a nearly complete elimination of the core level binding energy variation associated with the presence of a narrow $\ensuremath{\sigma}$ band in the C $1s$ state.