The resonating valence bond state in high Tc superconductors

As indicated by NMR experimental results, there are two types of electrons in a doped cuprate: the localized Cu3d electrons, which are responsible for magnetism, and the itinerant p-band electrons carrying the charge transports. We show that the uncompensated spins at oxygen sites created by holes can pair into a resonating valence bond (RVB) state via local exchange interactions where the quasi-free local Cu spins play a role of the mediation for spin pairing. The two-component model gives a proper interpretation of the magnetic origin of high T, superconductivity, especially, in explanation of the cross over from the anti-ferromagnetic to the RVB state.