  The superconductivity discovered in iron-pnictides is intimately related to a
nematic ground state, where the C4 rotational symmetry is broken via the
structural and magnetic transitions. We here study the nematicity in NaFeAs
with the polarization dependent angle-resolved photoemission spectroscopy. A
uniaxial strain was applied on the sample to overcome the twinning effect in
the low temperature C2-symmetric state, and obtain a much simpler electronic
structure than that of a twinned sample. We found the electronic structure
undergoes an orbital-dependent reconstruction in the nematic state, primarily
involving the dxy- and dyz-dominated bands. These bands strongly hybridize with
each other, inducing a band splitting, while the dxz-dominated bands only
exhibit an energy shift without any reconstruction. These findings suggest that
the development of orbital-dependent spin polarization is likely the dominant
force to drive the nematicity, while the ferro-orbital ordering between dxz and
dyz orbitals can only play a minor role here.
