The Spin Polaron Model and the Comparison with Liquid Helium

Abstract

This chapter introduces the concept of a spin polaron. All the spin polarons form pairs which are bosons with zero magnetic moment, the binding energy being some multiple of kTN ~ J. In an early paper, Anderson suggested that the clue to the understanding of the new superconductors could be a theory of the movement of charge caxriers in "Mott" insulators. It must be emphasized that the properties of the spin polarons differ strongly from those of a dielectric polaron. Thus for the former the mass increases with the size; for the latter the opposite is the case. In all copper oxide systems, the transition temperature at first rises with increasing x, that is with the increasing concentration of holes. The measured values of the Hall coefficient are not in general independent of temperature. Angle-resolved photoemission has been used to determine the Fermi surface, both above and below the transition temperature Tc.