  An exact particle-hole transformation is discovered in a local-moment model
for a single layer of heavily electron-doped FeSe. The model harbors hidden
magnetic order between the iron d_xz and d_yz orbitals at the wavenumber
(pi,pi). It potentially is tied to the magnetic resonances about the very same
Neel ordering vector that have been recently discovered in intercalated FeSe.
Upon electron doping, the local-moment model successfully accounts for the
electron-pocket Fermi surfaces observed experimentally at the corner of the
two-iron Brillouin zone in electron-doped FeSe, as well as for isotropic Cooper
pairs. Application of the particle-hole transformation predicts a surface-layer
iron-based superconductor at strong hole doping that exhibits high T_c, and
that shows hole-type Fermi-surface pockets at the center of the two-iron
Brillouin zone.
