Raman spectroscopy with UV excitation on untwinned single crystals of YBa2Cu3O7-

Recent reflectance anisotropy studies on the material showed a photobleaching effect in the in-plane components of the dielectric function around 2.2 and 4.1 eV [1]. We present Raman spectra of oxygen deficient YBa2Cu3O7- detwinned single crystals taken with laser excitation of 3.7 eV, close to the UV feature in the dielectric function, in search for a signal from the defect-induced Raman modes. While two groups of defect-induced mode at 230 cm-1 and 600 cm-1 behave very similar at the 2.2 eV resonance, we find clear differences for UV excitation. A peak at 600 cm-1 is identified as a copper-oxygen-chain related, defect-induced modes by its Raman selection rules. While this mode is enhanced beyond the strength of the Raman-allowed modes, the group at 230 cm^-1 is absent. Low temperature experiments showed no change of the peak height under illumination, though the peaks are known to photobleach in the visible.