PLANE-POLARIZED RAMAN CONTINUUM IN THE INSULATING AND SUPERCONDUCTINGLAYERED CUPRATES

Electronic properties of copper oxygen planes (and chains in Y-Ba-Cu-O ) were studied with Raman spectroscopy of plane-polarized photons. The electronic continuum was found to be independent of doping in 2:1:4 a nd 1:2:3 materials at energies above approximately 1000 cm-1. Temperat ure dependence at low energies differs significantly in undoped, light ly doped, and fully doped YBa2Cu3O6+x. A feature consistent with the s uperconducting gap was observed below T(c) in YBa2Cu3O6.9 in all scatt ering geometries. However, the gaplike redistribution was not complete , with 40-60% of states not shifted to higher energies at temperatures well below T(c). Above T(c) the temperature dependence strongly depen ds on scattering geometry: the continuum is temperature independent (m arginal-Fermi-liquid-like) in XX (x') and X'X' (x2+y2) geometry; it ha s a Bose-factor temperature dependence in X'Y' (x2-y2) geometry, and a weak temperature dependence somewhat smaller than the Bose factor in YY (y2) geometry. A two-boson-like temperature dependence of the low-e nergy continuum is found in YBa2Cu3O6.1 and Sm2CuO4. It becomes one-pa rticle-like in Y-Ba-Cu-O once small doping levels are introduced. Cons traints these results place on theoretical models are discussed.