Metal-insulator transition and superconductivity in Y1Ba2Cu3O7−x

Abstract

The oxygen concentration in the ${\mathrm{Y}}_1{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ superconducting compound has been changed by subjecting it to rapid quenching from temperatures in the range 500- 1000°C. The lower oxygen concentration destroys the superconductivity, causes removal of the orthorhombic distortion in the perovskite structure and results in a metal-insulator ($M-I$) transition. The presence of variable range hopping conductivity and thermopower in the insulating regime strongly suggests that the $M-I$ transition is of Anderson type. The results in general are understood in terms of the relative overlap between $d_{z^2}$ and $d_{x^2-y^2}$ components of the $e_g$ band of the octahedrally coordinated copper atoms.