  An intriguing aspect of unconventional superconductivity is that it always
appears in the vicinity of other competing phases, whose suppression brings the
full emergence of superconductivity. In the iron-pnictides, these competing
phases are marked by a tetragonal-to-orthorhombic structural transition and a
collinear spin-density-wave (SDW) transition. There has been macroscopic
evidence for competition between these phases and superconductivity as the
magnitude of both the orthorhombicity and magnetic moment are suppressed in the
superconducting state. Here, using angle-resolved photoemission spectroscopy on
detwinned underdoped $Ba_{1-x}K_xFe_2As_2$, we observe a coexistence of both
the SDW gap and superconducting gap in the same electronic structure.
Furthermore, our data reveal that following the onset of superconductivity, the
SDW gap decreases in magnitude and shifts in a direction consistent with a
reduction of the orbital anisotropy. This observation provides direct
spectroscopic evidence for the dynamic competition between superconductivity
and both SDW and electronic nematic orders in these materials.
