OXYGEN-CONCENTRATION DEPENDENCE OF THE RAMAN CONTINUA IN YBA2CU3OY SINGLE-CRYSTALS

The low-energy portion (omega less-than-or-equal-to 1200 cm-1) of the electronic Raman-scattering continua of YBa2Cu3Oy 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 B1g electronic continuum has been observed to be very sensitive to oxygen concentration. In particular a broad peak in the continuum shifts from 470 cm-1 to 550 cm-1 as y is reduced from 7.0 to 6.93. In contrast, the spectral distribution of the A1g continuum is essentially the same for all three crystals with y greater-than-or-equal-to 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 YBa2Cu3Oy. 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 B1g continuum arises at least in part from scattering from spin-density fluctuations.