RAMAN-SCATTERING IN YBA2CU3O7 SINGLE-CRYSTALS - ANISOTROPY IN NORMAL AND SUPERCONDUCTIVITY STATES

Precise temperature and polarization dependences of Raman spectra have been investigated for fully oxygenated twin-free YBa2Cu3O7 single cry stals. We have found a striking superconductivity-induced x-y anisotro py in the temperature behavior of the 340 cm(-1) line: the magnitudes of the softening and broadening are quite different in the xx- and yy- polarizations, This anisotropy suggests a contribution of the CuO-chai n superconductivity with a pairing symmetry different from that for th e CuO2 plane, or indicates that the superconducting gap amplitudes are different in the k(x) and k(y) directions. The d+s gap symmetry is th e only realistic symmetry in the case of Delta(x) not equal Delta(y). (C) 1998 American Institute of Physics. [S1063-7834(98)00403-1].