The low-energy portion (ω≤1200 ${\mathrm{cm}}^{\mathrm{-}1}$) of the electronic Raman-scattering continua of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{y}}$ single crystals with y=7.0, 6.99, and 6.93 has been investigated in a temperature range from 20 to 100 K. The frequency distribution of the ${\mathit{B}}_{1\mathit{g}}$ electronic continuum has been observed to be very sensitive to oxygen concentration. In particular a broad peak in the continuum shifts from 470 ${\mathrm{cm}}^{\mathrm{-}1}$ to 550 ${\mathrm{cm}}^{\mathrm{-}1}$ as y is reduced from 7.0 to 6.93. In contrast, the spectral distribution of the ${\mathit{A}}_{1\mathit{g}}$ continuum is essentially the same for all three crystals with y≥6.93. The dependence of the continua on oxygen concentration is compared to the results of previous measurements of the phonon anomalies associated with the Raman-active c-axis oxygen vibrations in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{y}}$. A symmetry-allowed correlation is established between the electronic continua and the phonon anomalies. Although the origin of the Raman continua remains undetermined, various possibilities are discussed and it is suggested that the ${\mathit{B}}_{1\mathit{g}}$ continuum arises at least in part from scattering from spin-density fluctuations.

• Received 21 May 1993

DOI:https://doi.org/10.1103/PhysRevB.48.10530