Spin density waves (SDWs) may be thought of as comprising charge density waves (CDWs) in pairs, with one CDW composed of up-spin electrons and the other composed of down-spin electrons. The superconductivity in cuprates may then be said to be caused by the BCS-type pairing of these SDWs. This is no longer a simple Cooper pairing of singlet electrons but one that involves a collection of Cooper pairs. Transport in normal metallic states is then governed by CDW pinning, as in a quantum well that is characterized by linear temperature dependence. The pseudo-gap may be understood as originating from this BCS-type gap with SDW, where the parameters used are from those of the original BCS scheme except that the electron–electron interaction is multiplied by N CDW , which is the number of electrons that have the same spin direction belonging to one CDW branch of the pair that comprises the SDW.
Novel topological phase due to coexistence of superconductivity and spin-density wave: Application to high Tc superconductors