We performed angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of the nematic phase in LaFeAsO. Degeneracy breaking between the dxz and dyz hole bands near the {Gamma} and M point is observed in the nematic phase.
Different temperature dependent band splitting behaviors are observed at the {Gamma} and M points. The energy of the band splitting near the M point decreases as the temperature decreases while it has little temperature dependence near the {Gamma} point. The nematic nature of the band shift near the M point is confirmed through a detwin experiment using a piezo device. Since a momentum dependent splitting behavior has been observed in other iron based superconductors, our observation confirms that the behavior is a universal one among iron based superconductors.
