ELECTRONIC RAMAN-SCATTERING OF TL-2201 AND TL-2223 AND THE SYMMETRY OF THE ENERGY-GAP

The high temperature superconductors Tl2Ba2CuO6+delta (Tl-2201) and Tl 2Ba2Ca2Cu3O10 (Tl-2223) with one and three CuO2 planes were investigat ed by Raman scattering in order to see whether the electronic Raman sc attering cross-section depends on the number of CuO2 planes, i.e. shee ts of the Fermi surface, We present measurements of polarized Raman sp ectra in different scattering geometries on two single crystals of Tl- 2201 (T-c = 90 K, 80 K), and one single crystal of Tl-2223 (T-c = 118 K), for temperatures below and above T-c. In B-1g-symmetry the peak in the electronic Raman scattering is found at 460 cm(-1)(T-c = 90 K), o r 430 cm(-1) (T-c = 80 K) for Tl-2201 and at 610 cm(-1) for Tl-2223. T his corresponds to 2 Delta/k(B)T(c) = 7.4 +/- 0.4 for both compounds. The A(1g)- and B-2g-symmetry components show smaller values for the pe ak position and a decrease linear in omega of the scattering intensity towards lower frequencies. The B-1g-component shows a decrease cubic in omega of the scattering intensity towards lower frequencies. The sp ectral features of Tl-2201 and Tl-2223 are found to be independent of the number of CuO2-planes, i.e. of specific details of the Fermi surfa ce. These observations are similar to the measurements on over- and un derdoped Bi2Sr2CaCu2O8+delta single crystals. They are consistent with a d(x1-y1)-wave pairing mechanism, based on the theoretical model of Devereaux and Einzel.