  The electronic structure near the Fermi level (EF) of Ba1-xKxFe2As2 (BaK122 ;
x = 0.2 - 0.7) is studied using laser ultrahigh-resolution angle-resolved
photoemission spectroscopy(ARPES). For the optimally doped case of x = 0.4, we
clearly observe two peaks below Tc in the ARPES spectra at a binding energies
(BE) of 5 meV and 13meV. The former is assigned to a superconducting (SC)
coherence peak since it appears and evolves below the bulk SC transition at Tc
(= 36 K), accompanying a gap opening centered at EF. In contrast, the latter
peak, which appears below ~ 90 K without any gap formation, is interpreted to
be not directly related to a SC coherence peak. This high-BE peak is observed
from x = 0.2 to 0.6, reduces in energy with overdoping (x > 0.4) and is absent
for x = 0.7. The temperature(T)- and doping-dependent ARPES results suggest
that the high-BE peak originates from coupling to a bosonic mode of energy ~ 8
meV.
