@article{ISI:000367396900014,
 abstract = {Nonequilibrium calculations in the presence of an electric field are
usually performed in a gauge, and need to be transformed to reveal the
gauge-invariant observables. In this work, we discuss the issue of gauge
invariance in the context of time-resolved angle-resolved pump/probe
photoemission. If the probe is applied while the pump is still on, one
must ensure that the calculations of the observed photocurrent are gauge
invariant. We also discuss the requirement of the photoemission signal
to be positive and the relationship of this constraint to gauge
invariance. We end by discussing some technical details related to the
perturbative derivation of the photoemission spectra, which involve
processes where the pump pulse photoemits electrons due to
nonequilibrium effects.},
 article-number = {014012},
 author = {Freericks, J. K. and Krishnamurthy, H. R. and Sentef, M. A. and
Devereaux, T. P.},
 doi = {10.1088/0031-8949/2015/T165/014012},
 eissn = {1402-4896},
 issn = {0031-8949},
 journal = {PHYSICA SCRIPTA},
 month = {OCT},
 orcid-numbers = {Sentef, Michael/0000-0002-7946-0282
Freericks, James K/0000-0002-6232-9165},
 researcherid-numbers = {Sentef, Michael/L-5717-2013
Freericks, James K/D-7502-2011},
 times-cited = {9},
 title = {Gauge invariance in the theoretical description of time-resolved
angle-resolved pump/probe photoemission spectroscopy},
 unique-id = {ISI:000367396900014},
 volume = {T165},
 year = {2015}
}