Theoretical Models of High-T _c Superconductivity

Abstract

The Bardeen–Cooper–Schrieffer (BCS) pairing theory in conventional superconductors is based on the picture of a Fermi liquid with a properly determined spectrum of single-electron excitations, “quasiparticles” near the Fermi surface (see Sect. 1.1). In cuprate superconductors, the normal state is unconventional and many electronic properties show anomalous behavior as discussed in Chap. 5. Therefore, a model that works perfectly well for a system of welldefined quasiparticles in conventional metals may be inapplicable to a system of strongly correlated electrons or at least the pairing theory should be modified to take into account the peculiarity of the normal state in cuprates. In this connection, in this chapter, we shall first discuss the problem of electronic structure and spectrum of single-electron excitations in the normal phase of cuprates.