We study superconducting FeSe (Tc=9K) exhibiting the tetragonal-orthorhombic structural transition (Ts∼90K) without any antiferromagnetic ordering, by utilizing angle-resolved photoemission spectroscopy. In the detwinned orthorhombic state, the energy position of the dyz orbital band at the Brillouin zone corner is 50meV higher than that of dxz, indicating the orbital order similar to the NaFeAs and BaFe2As2 families. Evidence of orbital order also appears in the hole bands at the Brillouin zone center. Precisely measured temperature dependence using strain-free samples shows that the onset of the orbital ordering (To) occurs very close to Ts, thus suggesting that the electronic nematicity above Ts is considerably weaker in FeSe compared to BaFe2As2 family.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 2014 Sept 29