Ion-Beam-Induced Metal-Insulator Transition in YBa sub 2 Cu sub 3 0 sub (7-delta): A Mobility Edge?

We have studied the temperature- dependent resistivity and Hall coefficient of epitaxial YBa sub 2 Cu sub 3 0 sub (7-delta) films as a function of ion-beam-induced damage. At low ion fluences the films behave like typical metals above the superconducting transition. At higher ion fluences, the material goes continuously through the metal-insulator transition with a resistivity that varies like exp(T sup (-1/1)) but with a Hall coefficient that changes very little. This implies that the transition is a result of a reduction in mobility rather than a drop in carrier density.