Variation of superconductivity with carrier concentration in oxygen-doped YBa2Cu3O7-y

The Hall coefficient RH, the volume fraction f showing the Meissner effect, and the superconducting transition temperature Tc have been measured in the high-Tc oxide YBa2Cu3O7-y for a range of oxygen vacancy concentration 0.0<y<0.7. We find that RH, f, and Tc are insensitive to y over the range 0.1<y<0.5. In this range, superconductivity at 55 K is possible (with a carrier density of 1.4×1021 cm-3), even with severe loss of connectivity in the CuO chains. The data are consistent with superconductivity occurring only in the CuO planes. A sharp transition in RH is also seen when y exceeds 0.50.