ELECTRONIC RAMAN-SCATTERING IN OPTIMALLY DOPED LA2-XSRXCUO4

The low energy electronic Raman cominua of a La1.83Sr0.17CuO4 single c rystal have been investigated in the x'y'(B-1g), xy(B-2g), xx(A(1g)+B- 1g) and x'x'(A(1g)+B-2g) scattering geometries. When the sample is coo led below the critical temperature T-c a superconductivity induced ren ormalization of the continue occurs and gap-like peaks are observed in ail geometries. The superconducting gap is anisotropic with maxims lo cated near the k(x) and k(y) axes. The maximum magnitude of the gap is given by omega(B-1g)=2 Delta(max)=7.7kT(c), which is similar to value s found in other optimally doped cuprates. The intensities in the low frequency portions of the B-1g and B-2g continua increase as omega(3) and omega respectively, a behaviour that is consistent with the existe nce of nodes along the diagonal \k(x)\=\k(y)\ directions in the recipr ocal lattice. The relative peak frequencies and intensities in the dif ferent scattering channels are also similar to those found in other cu prates. No spectral features have been identified that would enable on e to distinguish between compounds having a single CuO2 layer in the u nit cell and those having two closely spaced layers in a unit cell. Th e peak energies, omega(B-1g) and omega(B-2g), reach their maximum valu e very quickly when the sample is cooled below T-c, indicating that th e gap opens very rapidly. Finally, the results have been compared to t he predictions of the conventional model of light scattering fi am sup erconductors and differences are discussed. (C) 1998 Elsevier Science B.V.