Low-temperature Hall effect inBi2Sr2CuO6−δ

The single-layer oxide supeconductor ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_{6\mathrm{-}\mathrm{\delta }}$ offers an opportunity to study the normal-state properties of the cuprate superconductors down to low temperatures, but crystals of this material display a wide range of stoichiometry and properties. We report measurements of the resistivity and Hall coefficient ${\mathit{R}}_{\mathit{H}}$ on crystals whose cation and oxygen stoiochiometries have been determined to an accuracy of 1 to 2%. In superconducting samples there is a pronounced maximum in ${\mathit{R}}_{\mathit{H}}$ at 70 K, which we argue to be a characteristic feature of cuprate superconductors in the normal state.