Raman measurements of YBa2Cu3O7−δ single crystals

We report polarized Raman scattering from YBa2Cu3O7−δ single crystals, which have Tc values between 92.5 K and 0 K, and compare our data to other reported single crystal Raman results. In samples with Tc < 90 K, three prominent lines are observed at 140, 340, and 456 cm-1 for (xx) polarization. We also observe lines in (zz) and (xz) polarization. In crystals with Tc = 92.5 K the spectra are weaker and more complex, although measurable. Using our results, a number of the reported differences are resolved, and the phonons are discussed. The change in Raman spectra with oxygen content is discussed in terms of a phase separation hypothesis, proposed in a recent theoretical paper.