Journal
JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA
Volume 253, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.elspec.2021.147121
Keywords
Time- and angle-resolved photoemission; Nonequilibrium Green's functions; Graphene
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Funding
- U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-AC02-76SF00515]
- Alexander von Humboldt Foundation, Germany
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) via the Emmy Noether program [SE 2558/2]
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Motivated by recent experimental progress, we revisit the theory of pump-probe time- and angle-resolved photoemission spectroscopy (trARPES), which is one of the most powerful techniques to trace transient pump-driven modifications of the electronic properties. We introduce the theory of time-resolved photoemission within both gauges from the perspective of nonequilibrium Green's functions, we investigate the gauge invariance, and discuss typical effects observed in subcycle time-resolved photoemission. The formalism presented is an ideal starting point for realistic trARPES simulations including scattering effects.
Motivated by recent experimental progress we revisit the theory of pump-probe time- and angle-resolved photoemission spectroscopy (trARPES), which is one of the most powerful techniques to trace transient pump-driven modifications of the electronic properties. The pump-induced dynamics can be described in different gauges for the light-matter interaction. Standard minimal coupling leads to the velocity gauge, defined by linear coupling to the vector potential. In the context of fight-binding (TB) models, the Peierls substitution is the commonly employed scheme for single-band models. Mull-orbital extensions - including the coupling of the dipole moments to the electric field - have been introduced and tested recently. In this work, we derive the theory of time-resolved photoemission within both gauges from the perspective of nonequilibrium Green's functions. This approach naturally incorporates the photoelectron continuum, which allows for a direct calculation of the observable photocurrent. Following this route we introduce gauge-invariant expressions for the time-resolved photoemission signal. The theory is applied to graphene pumped with short terahertz pulses, which we treat within a first-principles TB model. We investigate the gauge invariance and discuss typical effects observed in subcycle time-resolved photoemission. Our formalism is an ideal starting point for realistic trARPES simulations including scattering effects.
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