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L.V. Gasparov, P. Lemmens, M.B. Brinkmann, N.N. Kolesnikov, G. Guntherodt.
Electronic Raman scattering in the single - CuO₂ layered superconductor Tl₂Ba₂CuO_6+d.

  Abstract:
Electronic Raman scattering in Tl₂Ba₂CuO_6+d   (Tl-2201) has been investigated in order to test whether the scattering cross section in high-temperature superconductors depends on the number of CuO₂ planes, i.e., sheets specific details of the Fermi surface. The polarized Raman spectra have been measured in different scattering geometries for temperatures above and below T_c . The spectral features of Tl-2201 with one CuO₂ plane per unit cell are found to be similar to Tl₂Ba₂Ca₂Cu₃O₁₀ which  three CuO₂  planes and those of other high - temperature superconductors with several CuO₂  planes per unit cell. The peak in the B_1g symmetry component of the scattering intensity is found at 460 cm^-1 (T_c=90 K), or 430 cm^-1 (T_c=80 K). The B_1g  peak positions scale with T_c, and correspond to 2D/k_BT_c = 7.6±0.4. The temperature dependence of the B_1g scattering component of Tl-2201 (T_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 d _x2_{- y}2 wave symmetry of the order parameter used in the description of the Raman-scattering cross section.