Orbital-Dependent Modifications of Electronic Structure across the Magnetostructural Transition inBaFe2As2

Laser angle-resolved photoemission spectroscopy (ARPES) is employed to investigate the temperature ($T$) dependence of the electronic structure in ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ across the magnetostructural transition at $T_N\sim 140\mathrm{K}$. A drastic transformation in Fermi surface (FS) shape across $T_N$ is observed, as expected by first-principles band calculations. Polarization-dependent ARPES and band calculations consistently indicate that the observed FSs at $k_z\sim \pi$ in the low-$T$ antiferromagnetic state are dominated by the $\mathrm{Fe}3d_{zx}$ orbital, leading to the twofold electronic structure. These results indicate that magnetostructural transition in ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ accompanies orbital-dependent modifications in the electronic structure.