  We present a systematic photoemission study of the newly discovered high Tc
superconductor class (Sr/Ba)1-xKxFe2As2. By utilizing a unique photon energy
range and scattering geometry we resolve the details of the single particle
dynamics of interacting electrons on the central Fermi surfaces of this series
which shows overall strong coupling behavior (2D/kBTc = 6). Quasiparticle
dispersion kinks are observed in a binding energy range of 15 to 50 meV which
matches the magnetic excitation energy scales (parameterized by J1,J2). The
size of the Cooper pair wavefunction is found to be less than 20A indicating a
short in-plane scale uncharacteristic of a BCS-phonon scenario but suggestive
of a phase factor in the global order parameter. The kink likely reflects
contributions from the strongly frustrated fluctuating spin excitations and the
soft phonons around 20-40 meV. Our results provide important clue to the nature
of the pairing potential realized in these superconductors.
