The η-Pairing Superconductivity in Spin-Density Wave Background

In this letter, we propose a modified attractive Hubbard model at half filling that can exhibit superconductivity through η-pairing mechanism in spin-density wave representation and derive a concise relationship between the energy disparity and the single-particle energy spectrum. This relationship, in the two limits of U, clearly shows that the system does not display superconductivity for very low doping concentration. but demonstrates superconductivity when the doping concentration exceeds a certain critical value. This conclusion is in qualitative agreement with the familiar experiments on high-T_c superconductivity.