Magneto-orbital coupling in iron pnictides

A magneto-orbital coupling mechanism is proposed to account for the weak energy gap at the Fermi energy in the $(π,0)$ ordered SDW state of a realistic three band model for iron pnictides involving $d_xz$, $d_yz$, and $d_xy$ Fe orbitals. The orbital mixing terms between the $d_xy$ and $d_xz/d_yz$ orbitals, which are important in reproducing the orbital composition of the elliptical electron pockets at $(\pm π,0)$ and $(0,\pm π)$, are shown to play a key role in the energy gap formation in the SDW state.