Superconductivity of Itinerant Electrons Coupled to Spin Chains

Abstract

Let us take as our starting point the Cu-O layers. The question is this: if one dopes the system away from half filling is there a mechanism that can lead to superconductivity? We will also assume that the carriers reside at the oxygen sites and that the spins in the copper sites provide an antiferromagnetic background for the former. A possible mechanism for pairing is due to spin polarons. Consider just one carrier: if there is a coupling between the spins of the itinerant electrons (IE) and the fixed spins (say ferromagnetic), then the carriers will prefer a ferromagnetic domain (aligned with its spin), i.e. a polaron. The polaron size will be determined by a competition between loss of exchange energy and localization energy. If a second carrier is now introduced, it will reside in the same polaron (if the coulomb interaction is not too strong) and also have its spin parallel to the first. Thus the polaron can lead to pairing in the spin 1 channel.