Effects of lead doping on Tc and energy gap of Bi2Sr2CaCu2O8 by tunneling spectroscopy

Doping the high-T-c superconductor Bi2Sr2CaCu2O8 (Bi-2212) with lead causes a partial substitution of the Bi atoms between the conducting CuO2 planes, and modifies some of the electronic and structural properties of the material. We have studied Pb-doped Bi-2212 single crystals using a tunneling technique. We find that while Pb doping decreases T-c significantly, it has a minimal effect on the in-plane energy gap, leading to an increase in the reduced gap, 2 Delta/kT(c). This result is consistent with other studies of the effects of in plane dopants on Bi-2212, but is the first evidence of such an effect attributable to defects introduced out of the plane. Inspection of the physical evidence leads to the conclusion that the inter-layer coupling has been modified and indicates a connection between high-T-c superconductivity and the inter-layer coupling between the CuO2 planes. (C) 1998 Elsevier Science B.V.