SUPERCONDUCTING ENERGY-GAP IN BI-CUPRATES

Tunneling spectroscopy has been performed on the polycrystalline super conductor Bi2.07Sr1.6La0.4CuO6+x (La2201) with transition temperature T-c = 30 K at 4.2 K. The measured tunneling spectra (tunneling conduct ance versus the bias voltage) on La2201 reveal a significant reduction below a certain voltage indicating the superconducting gap edge. The BCS-like formula for the superconducting density of states has been us ed to fit the experimental data at the gap-like peak taking account fo r the, broadening. The superconducting energy gap is compared with the result for four other Bi-cuprates (Bi,Pb)(2)Sr2Ca2Cu2O10+x (2223), Bi 2Y0.1Sr1.9CaCu2O8+x (Y2212), Bi2.1Sr1.9CaCu2O8+x (2212), and Bi2.07Sr1 .8CuO6+x (2201) with the transition temperatures T-c = 108, 94, 85 and 7 K, respectively. In all systems, with the wide range of T-c's spann ing from 7 to 108 K, the obtained values of the reduced superconductin g energy gap 2 Delta/k(B)T(c) amount to approximately the same value 6 -7, i.e. the gap 2 Delta scales with the transition temperature T-c in the Bi-cuprates.