Evolution of magnetic and superconducting fluctuations with doping of high-Tc superconductors:: An electronic Raman scattering study

For YBa2Cu3O6+delta and Bi2Sr2CaCu2O8+/-delta superconductors, electronic Raman scattering from high- and low-energy excitations has been studied in relation to the hole doping level, temperature and energy of the incident photons. For underdoped superconductors, it is concluded that short range antiferromagnetic (AF) correlations persist with hole doping and doped single holes are incoherent in the AF environment. Above the superconducting (SC) transition temperature T-c, the system exhibits a sharp Raman resonance of B-1g symmetry and about 75 meV energy and a pseudogap for electron-hole excitations below 75 meV, a manifestation of a partially coherent state forming from doped incoherent quasi-particles. The occupancy of the coherent state increases with cooling until phase ordering at T-c produces a global SC state. (C) 1998 Elsevier Science Ltd. All rights reserved.