NORMAL STATE PROPERTIES IN THE CUPRATES AND THEIR FERMI-LIQUID BASED INTERPRETATION

A central issue in the field of high temperature superconductivity is the nature of the normal state. Here we review normal state transport, thermodynamic, magnetic and spectroscopic data and discuss their interpretation within a Fermi liquid based framework. Comparison with other highly correlated systems, such as the heavy fermion metals and the quantum liquid He-3, is also presented. It is demonstrated that the cuprate data are not consistent with canonical Fermi liquid behavior. However, if the Fermi liquid is characterized by low energy scales, arising from narrow bandwidths or soft spin fluctuations, then canonical behavior is not expected at the relatively "high" temperatures of the normal state. In this way anomalies above T(c) may be reconciled with a Fermi liquid (ground state) picture. Here we review the two main Fermi liquid based schools and their interpretation of the data. These are the "almost localized" and "almost magnetic" Fermi liquid descriptions. The dichotomy between these two near-instabilities has appeared in the context of the heavy fermions as well as liquid He-3 and seems to be generally associated with highly correlated systems. Both approaches have addressed the data with some success and it is clear that they are, in many respects, closely related. The relationship between other Fermi-liquid-like, as well as more unconventional schemes is also addressed. Here it is claimed that the strongest support for a Fermi liquid based approach to the cuprates derives from the comparison with other strongly correlated Fermi liquid systems, which exhibit similar normal state anomalies.