Raman scattering in TlmBa2Can-1CunO2(n+1)+m superconducting crystals

The Raman spectra of single crystals of the high temperature superconductors Tl2Ba2CuO6-x, Tl2Ba2CaCu2O8-x and TlBa2CaCu2O7-x are measured at temperatures between 10 and 300 K. A factor group analysis of the zone center phonons for TlmBa2Can-1CunO2(n+1)+m compounds with m=1, n=2, 3 and m=2, n=1-3 is carried out. All observed modes are of A1g symmetry. No anomaly is observed in the temperature dependence of the phonon frequencies and line widths. An assignment of all observed A1g modes is proposed. The causes of the low Raman activity of the B1g mode of the Tl2Ba2CaCu2O8-x and TlBa2CaCu2O7-x superconductors are discussed. The observed asymmetry in the shape of the Raman lines is tentatively ascribed to electron-phonon coupling