LAUSR

The remarkable $s\pm$ superconductivity (SC) is well known in the iron-based superconductors, which are of multi-orbital characteristic. Here we propose a single-orbital realization of this intriguing pairing state with high superconducting critical temperature $T_c$ in the square-octagon lattice, which is hosted by a few real materials. Owing to the perfect Fermi surface nesting at half-filling, arbitrarily weak Hubbard-interaction drives long-range spin-density wave (SDW) with Neel antiferromagnetic order. Such SDW order persists into the doped regime for finite Hubbard-$U$, but with its wave-vector shifting linearly with doping concentration, leading into incommensurate SDW state. When such SDW order is killed by further doping or parameter-tuning, strong short-ranged spin fluctuations mediate unconventional SC with rich pairing phase-diagram. The largest portion of the phase-diagram is occupied by the $s\pm$-SC, with high $T_c$. Finally, we propose realization of our results in relevant materials.