Effect of oxygen stoichiometry on electronic Raman scattering in YBa 2Cu 3O x (7.0 > x > 6.8)

Abstract

The polarized electronic Raman response of YBaCuO (Y-123) single crystals and polycrystals with oxygen stoichiometries of 7.0, 6.9, and 6.8 and its temperature dependent redistribution in the normal and superconducting states has been investigated for frequency shifts between 70cm−1 and 2000cm−1. Polarized spectra of polycrystalline samples were found to yield a predominantly zz polarized (i.e.∥ c-axis) response. In the normal state temperature dependencies differ displaying Bose-Einstcin and quasi-Fermi-liquid behaviors for the zz dominated polycrystal and single crystal xx polarizations respectively but are found to be essentially independent of oxygen stoichiometry. In the superconducting (SC) state partial gap formation by condensation of charge density fluctuations below 200cm−1 and pair breaking peak enhancement of the electronic Raman response between 200cm−1 and 330cmt−1 appears independent of oxygen stoichiometry in the zz dominated polycrystals. Comparison to the known xx SC response yields similar gap values but smaller pairbreaking peak widths indicating greater quasiparticle lifetimes or smaller momentum transfer. Enhanced subgap zz polarized electronic excitations observed at 10K only in the oxygen depleted sample (O = 6.8) and similar xx excitations in Y-123 and Y-124 possibly suggest that they originate from the Cu(1)-O(1) chain bands.