FeSCs.

![image](Fig2){width="95.00000%"}

The low temperature electronic structure of [K$_{x}$Fe$_{2-y}$Se$_2$]{}is shown in Fig. \[fig:fig1\]. The Fermi surface (FS) of KFS consists of large electron pockets at the Brillouin zone (BZ) corner-X point, and a small electron pocket at the BZ center-$\Gamma$ point (Fig. \[fig:fig1\](a)), consistent with previous ARPES reports [@24zhang11; @25qian11; @26mou11]. For the crystallographic 2-Fe unit cell, LDA calculations predict two electron pockets at the X point [@27nekrasov11] (Fig. \[fig:fig1\](i)). While FS map appears to show only one electron pocket at X, measurements under different polarizations (Fig. \[fig:fig1\](j)-(l)) reveal the expected two electron bands with nearly degenerate Fermi crossings ([$k_F$]{}) but different band bottom positions-a shallower one around -0.05eV and a deeper one that extends to the top of the [$d_{xz}$/$d_{yz}$]{} hole-like bands at -0.12eV. The Luttinger volume of the two electron pockets gives $\sim$0.16 electrons per Fe. Considering that the C$_4$ symmetry of the crystal dictates degeneracy of the [$d_{xz}$/$d_{yz}$]{} electron band bottom and hole band top at X, the shallower electron band that is not degenerate with the hole-like band at higher binding energy is most likely of [$d_{xy}$]{} character, and the deeper one [$d_{xz}$]{} along $\Gamma$-X and [$d_{yz}$]{} along the perpendicular direction. This observed orbital character assignment 