Binding Energy of Holes in the Two d-π Chains

I propose new two chains composed of d electrons with localized spin 1/2 and itinerant π electrons to research the possibility of superconductivity with spin gaps in organic compounds. I have investigated the effects of the antiferromagnetic exchange interaction between d- and π-electron spins, JK, that between π-electron spins along the rung, Jv, and the transfer energy of π electron along the rung, tv, on the bound states of holes. I have computed the binding energy EBof two holes doped away from half-filling using a mean-field approximation and periodic boundary conditions. As JKand Jvincrease, EB's decrease and are negative for larger values than the critical values JKcand Jvc, while EB< 0 for smaller values of tvthan tvc. As a result, the holes on rungs form a bound state and the bound states are stabilized for JK≥ JKc, Jv≥ Jvcand tv≤ tvc. The spin of two holes is singlet.