SIGNATURE OF THE D-WAVE GAP PARAMETER IN THE FIELD-DEPENDENCE OF THE ELECTROTHERMAL CONDUCTIVITY OF HIGH-T-C SUPERCONDUCTORS UP TO T-C

We calculate the influence of a magnetic field on a transport property like the electrothermal conductivity P of high-T-c superconductors fo r either an anisotropic (or not) s-wave or a d(x2-y2)-wave gap paramet er. The field dependence of the electrothermal conductivity of Bi2Sr2C aCu2O8, (BiPb)(2)Sr2Ca2Cu3O10, and Tl2Ba2CaCu2O8 compounds near T-c is then analyzed. It is shown that the behavior is consistent with a gap parameter of d(x2-y2)-wave type for reasonable values of the physical parameters and excludes an anisotropic (or not) s-wave symmetry over a temperature range extending up to T-c.