Evolution of magnetic and superconducting fluctuations with doping of high-T-c superconductors

Electronic Raman scattering from high-and low-energy excitations was studied as a function of temperature, extent of hole doping, and energy of the incident photons in Bi2Sr2CaCu2O8+/-delta superconductors, For underdoped superconductors, short-range antiferromagnetic (AF) correlations were found to persist with hole doping, and doped single holes were found to be incoherent in the AF environment. Above the superconducting (SC) transition temperature T-c, the system exhibited a sharp Raman resonance of B-1g symmetry and energy of 75 millielectron-volts and a pseudogap for electron-hole excitations below 75 millielectron-volts, 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.