Charge transfer and carrier density in Bi-2212 high-Tc superconductors

Muon spin relaxation and neutron diffraction measurements were performed in Y and Pb substituted Bi-2212 superconductors in order to study the correlation between T c and hole density. We observe first an increase of both T c and the superconducting carrier density via hole transfer, but subsequently (at higher “doping”) more and more holes are prevented from forming superconducting pairs.