  The electronic structure of NaFeAs is studied with angle resolved
photoemission spectroscopy on high quality single crystals. Large portions of
the band structure start to shift around the structural transition temperature,
and smoothly evolve as the temperature lowers through the spin density wave
transition. Moreover, band folding due to magnetic order emerges around
structural transition. Our observation provides direct evidence that the
structural and magnetic transitions share the same origin, and are both driven
by the electronic structure reconstruction in Fe-based superconductors, instead
of Fermi surface nesting.
