Interorbital nematicity and the origin of a single electron Fermi pocket in FeSe

The electronic structure of the enigmatic iron-based superconductor FeSe has puzzled researchers since spectroscopic probes failed to observe expected electron pocket at $Y$ point in 1-Fe Brillouin zone. It been speculated that this pocket, essential for an understanding superconducting state, is either absent or incoherent. Here, we perform a theoretical study preferred nematic order originating from nearest-neighbor Coulomb interactions model relevant FeSe. We find low temperatures dominating components are interorbital ${d}_{xz}\text{\ensuremath{-}}{d}_{xy}$ and ${d}_{yz}\text{\ensuremath{-}}{d}_{xy}$ character, with spontaneously broken amplitudes these two components. This naturally leads distinct hybridization gaps $X$ points zone, may thereby produce highly anisotropic Fermi surfaces only single one momentum-space locations. associated gap obtained generated low-energy band spin-fluctuation mediated pairing agrees well measured experimentally. Finally, comparison computed spin susceptibility available neutron scattering data, discuss necessity additional self-energy effects, explore role orbital-dependent quasiparticle weights as minimal means include them.