M.Kang, G. Blumberg, M.V. Klein, N.N. Kolesnikov.
Resonance Raman study of superconducting gap and low energy excitations in Tl₂Ba₂CuO_6+d superconductors.

  Abstract:
Low energy electronic Raman scattering from  Tl₂Ba₂CuO_6+d   single crystals with T_c= 25 and 85 K has been studied using excitation energies from 1.65 to 3.05 eV. The B_1g  2D peak position shows that the 2D/k_BTc value decreases as the doping level increases. The resonance profiles of the 2D peak and the continuum show similar and strong resonances towards the 3.4 eV optical absorption peak in both crystals, which indicates that (1) the 2D peak and the continuum are coupled to light scattering by the same mechanism, and (2) the light scattering mechanism for both features involves the 3.4 eV optical absorption process.