Variable Hall coefficient in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8\mathrm{-}\mathrm{x}}$ across the metal-insulator transition

Measurements are reported of the Hall coefficient $R_H$ and ab-plane resistivity for single-crystal ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8\mathrm{-}\mathrm{x}}$, with variable oxygen configuration. As the system is driven through the metal-‘‘insulator’’ transition, $R_H$ increases strongly but continues to obey the empirical expression 1/$R_H$=γ+βT, where T is the temperature. For low oxygen content the Hall mobility ${\mu }_H$ becomes temperature independent. We examine these results in terms of various normal-state transport models.