STM STS AND ELECTRONIC SPECIFIC-HEAT OF HIGH-T-C CUPRATES - SYMMETRY OF THE ORDER-PARAMETER/

We investigated features of the superconducting gap of Bi2Sr2CaCu2O8+d elta by STM/STS and La2-xSrxCuO4 by measuring the electronic specific heat C-el. STS spectra were measured in the same processes as in obser vations of STM images at low bias voltage eV(0) = 20 meV. The supercon ducting gap structure in the STS spectra can be explained very well in terms of a d(x2-y2) superconductor with an anisotropic Fermi surface within the k(x)-k(y) plane. In superconducting La2-xSrxCuO4 (0.16 less than or equal to x less than or equal to 0.22), the electronic specif ic heat C-el is found to exhibit a T-2 dependence at T much less than T-c, and substitution of 0.3-0.5% Zn for Cu changes the T-2 dependence into a quite different one, described by the sum of T linear and T-3 terms. These features of C-el give convincing evidence for a clean sup erconductor with lines of nodes in the gap.