Superconducting order parameter in partially substituted ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathrm{x}}$ single crystals as measured by the tunneling effect

Tunneling-spectroscopy measurements have been performed on pure and Ni- and Zn-substituted ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathrm{x}}$ single crystals using a scanning tunneling microscope and a break-junction setup. The superconducting energy gap for the Ni-doped samples was found to be larger with respect to the pure samples. Anomalies have also been found in the temperature dependence of the gap for the Ni-substituted samples.