Variation of superconductivity with carrier concentration in oxygen-dopedYBa2Cu3O7−y

The Hall coefficient $R_H$, the volume fraction $f$ showing the Meissner effect, and the superconducting transition temperature $T_c$ have been measured in the high-$T_c$ oxide $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ for a range of oxygen vacancy concentration $0.0<y<\mathrm{}0.7\mathrm{}$. We find that $R_H$, $f$, and $T_c$ are insensitive to $y$ over the range $0.1<y<\mathrm{}0.5\mathrm{}$. In this range, superconductivity at 55 K is possible (with a carrier density of 1.4×${10}^{21}$ ${\mathrm{cm}}^{-3\mathrm{}}$), 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 $R_H$ is also seen when $y$ exceeds 0.50.