Raman Investigation of Zn-Doped YB$_{2}$Cu$_{3}$O$_{6.99}$ Single Crystals

We report the results of a Raman scattering study of the effects of doping YBa$_{2}$Cu$_{3}$O$_{6.99}$ crystals with 1.0{\%} Zn, which decreased the critical temperature from 92K to 81K. We found that the strength and shape of the 340cm$^{-1}$ B1g phonon anomaly are nearly the same in both the doped and undoped crystals. This observation suggests that Zn-doping does not significantly change the hole concentration. Furthermore, we extracted the B1g electronic continuum by removing the phonon contributions using a decoupling procedure. The resulting electronic spectra from the Zn- doped and undoped crystals are again essentially identical and are consistent with the scattering of light by the superconducting quasi-particles across a d-wave gap. The equal intensities of the B1g electronic continua again indicates that the carrier concentrations are the same in both the Zn-doped and undoped crystals. This in turn implies that Zn-doping does not lead to the opening of a pseudo gap.