  We investigate the transient electronic structure of BaFe2As2, a parent
compound of iron-based superconductors, by time- and angle-resolved
photoemission spectroscopy. In order to probe the entire Brillouin zone, we
utilize extreme ultraviolet photons and observe photoemission intensity
oscillation with the frequency of the A1g phonon which is antiphase between the
zone-centered hole Fermi surfaces (FSs) and zone-cornered electron FSs. We
attribute the antiphase behavior to the warping in one of the zone-centered
hole FSs accompanying the displacement of the pnictogen height, and find that
this displacement is the same direction as that induced by substitution of P
for As, where superconductivity is induced by a structural modification without
carrier doping in this system.
