Time- and angle-resolved photoelectron spectroscopy of strong-field light-dressed solids: Prevalence of the adiabatic band picture

In recent years, strong-field physics in condensed matter was pioneered as a potential approach for controlling material properties through laser dressing, as well as for ultrafast spectroscopy via nonlinear light-matter interactions (e.g., harmonic generation). A potential controversy arising from these advancements is that it is sometimes vague which band picture should be used to interpret strong-field experiments: The field-free bands, the adiabatic (instantaneous) field-dressed bands, Floquet bands, or some other intermediate picture. Here, we try to resolve this issue by performing theoretical experiments of time- and angle-resolved photoelectron spectroscopy (Tr-ARPES) for a strong-field laser-pumped solid, which should give access to the actual observable bands of the irradiated material. To our surprise, we find that the adiabatic band picture survives quite well up to high field intensities (similar to 10(12) W/cm(2)) and in a wide frequency range (driving wavelengths of 4000 to 800 nm, with Keldysh parameters ranging up to similar to 7). We conclude that, to first order, the adiabatic instantaneous bands should be the standard blueprint for interpreting ultrafast electron dynamics in solids when the field is highly off resonant with characteristic energy scales of the material. We then discuss weaker effects of modifications of the bands beyond this picture that are nonadiabatic, showing that by using bichromatic fields the deviations from the standard picture can be probed with enhanced sensitivity. In this paper, we outline a clear band picture for the physics of strong-field interactions in solids, which should be useful for designing and analyzing strong-field experimental observables and to formulate simpler semi-empirical models.