The `spin gap' in cuprate superconductors

Abstract

We discuss some generalities about the spin gap in cuprate superconductors and, in detail, how it arises from the interlayer picture. It can be thought of as spinon (uncharged) pairing, which occurs independently at each point of the 2D Fermi surface because of the momentum selection rule on interlayer superexchange and pair tunnelling interactions. Some predictions can be made.