  The FeSe nematic phase has been the focus of recent research on iron based
superconductors (IBSs) due to its unique properties. A number of electronic
structure studies were performed to find the origin of the phase. However, such
attempts came out with conflicting results and caused additional controversies.
Here, we report results from angle resolved photoemission and X-ray absorption
spectroscopy studies on FeSe with detwinning by a piezo stack. We have fully
resolved band dispersions with orbital characters near the Brillouin zone
corner which reveals absence of a Fermi pocket at the Y point in the 1Fe
Brillouin zone. In addition, the occupation imbalance between dxz and dyz
orbitals is found to be opposite to that of iron pnictides, which is consistent
with the identified band characters. These results settle down controversial
issues in the FeSe nematic phase and shed light on the origin of nematic phases
in IBSs.
