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Søren Ulstrup

Extracting the temperature of hot carriers in time- and angle-resolved photoemission

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The interaction of light with a material’s electronic system creates an out-of-equilibrium (nonthermal)
distribution of optically excited electrons. Non-equilibrium dynamics relaxes this distribution
on an ultrafast timescale to a hot Fermi-Dirac distribution with a well-defined temperature.
The advent of time- and angle-resolved photoemission spectroscopy (TR-ARPES) experiments has
made it possible to track the decay of the temperature of the excited hot electrons in selected states
in the Brillouin zone, and to reveal their cooling in unprecedented detail in a variety of emerging
materials. It is, however, not a straightforward task to determine the temperature with high accuracy.
This is mainly attributable to an a priori unknown position of the Fermi level and the fact that the
shape of the Fermi edge can be severely perturbed when the state in question is crossing the Fermi
energy. Here, we introduce a method that circumvents these difficulties and accurately extracts both
the temperature and the position of the Fermi level for a hot carrier distribution by tracking the occupation
statistics of the carriers measured in a TR-ARPES experiment
Original languageEnglish
Article number013907
JournalReview of Scientific Instruments
Publication statusPublished - 31 Jan 2014

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