Bose-Einstein to BCS crossover as a model for high-Tc cuprate superconductors

Crossover from Bose-Einstein (BE) to BCS condensation can be a guiding principle in understanding the evolution of high-Tc cuprate superconductors as a function of carrier doping. This picture is developed by combining two experimental results: (1) the "universal correlations" between T-c and n(s)/m(*) (superconducting carrier density/effective mass) found in mu SR measurements of the magnetic field penetration depth lambda and (2) the "pseudo gap" behavior observed in NMR, neutron scattering, dc- and optical conductivity, specific heat, and most-recently in angle-resolved photo-emission (ARPES) measurements. Here we provide a critical review of these experimental results and the relevant theoretical work in order to elucidate the essential features of this crossover picture and to discuss condensation mechanisms in the cuprates.