Electronic Raman scattering in the single-${\mathrm{CuO}}_2$ layered superconductor ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{CuO}}_{6+\mathrm{\delta }}$

Electronic Raman scattering in ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{CuO}}_{6+\mathrm{\delta }}$ (Tl-2201) has been investigated in order to test whether the scattering cross section in high-temperature superconductors depends on the number of ${\mathrm{CuO}}_2$ planes, i.e., sheets or specific details of the Fermi surface. The polarized Raman spectra have been measured in different scattering geometries for temperatures above and below ${\mathrm{T}}_{\mathrm{c}}$. The spectral features of Tl-2201 with one ${\mathrm{CuO}}_2$ plane per unit cell are found to be similar to ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{10}$ with three ${\mathrm{CuO}}_2$ planes and those of other high-temperature superconductors with several ${\mathrm{CuO}}_2$ planes per unit cell. The peak in the ${\mathrm{B}}_{1\mathrm{g}}$ symmetry component of the scattering intensity is found at 460 ${\mathrm{cm}}^{\mathrm{-}1}$(${\mathrm{T}}_{\mathrm{c}}$=90nK), or 430 ${\mathrm{cm}}^{\mathrm{-}1}$(${\mathrm{T}}_{\mathrm{c}}$=80nK). The ${\mathrm{B}}_{1\mathrm{g}}$ peak positions scale with ${\mathrm{T}}_{\mathrm{c}}$, and correspond to 2Δ/${\mathrm{k}}_{\mathrm{B}}$ ${\mathrm{T}}_{\mathrm{c}}$=7.6±0.4. The temperature dependence of the ${\mathrm{B}}_{1\mathrm{g}}$ scattering component of Tl-2201 (${\mathrm{T}}_{\mathrm{c}}$=80 and 90 K) reveals a deviation from BCS behavior. The experimental data are in qualitative agreement with the calculations of Devereaux and Einzel based on the ${\mathrm{d}}_{{\mathrm{x}}^2\mathrm{-}{\mathrm{y}}^2}$-wave symmetry of the order parameter used in the description of the Raman-scattering cross section.