ELECTRONIC RAMAN-SCATTERING IN TL2BA2CUO6- SYMMETRY OF THE ORDER-PARAMETER, OXYGEN DOPING EFFECTS, AND NORMAL-STATE SCATTERING(DELTA )

Single crystals of the optimally doped, moderately and strongly overdo ped high-temperature superconductor Tl2Ba2CuO6+delta (T1-2201) with T- c= 80, 56, and 30 K, respectively, have been investigated by polarized Raman scattering. By taking the peak position of the B-1g component o f electronic Raman scattering as 2 Delta(0) we found that the reduced gap value (2 Delta(0)/k(B)T(c)) strongly decreases with increasing dop ing. The behavior of the low-frequency scattering for the B-1g and B-2 g scattering components is similar for optimally doped and overdoped c rystals and can be described by a omega(3) and omega law, respectively , which is consistent with a d-wave symmetry of the order parameter. I n contrast to the optimally doped T1-2201 in both moderately and stron gly overdoped T1-2201, the relative (compared to the Big) intensity of the A I, scattering component is suppressed. We suggest that the van Hove singularity is responsible for the observed changes of Raman inte nsity and reduced gap value with doping. Electronic Raman scattering i n the normal state is discussed in the context of the scattering from impurities and compared to the existing infrared data. The scattering rate evaluated from the Raman measurements is smaller for the overdope d samples, compared to the moderately overdoped samples. [S0163-1829(9 8)06641-7].