Pressure dependence of the resistivity and magnetoresistance in single-crystal

We have measured the resistivity and magnetoresistance of single-crystal as a function of hydrostatic pressure up to 12 kbar. The pressure dependence of the resistivity at temperatures near the metal - insulator transition exceeds , greater than that observed in the normal state of high-temperature superconductors. The extreme pressure sensitivity of the resistivity below the transition temperature provides evidence that the low-temperature phase is not a simple metal. The metal - insulator transition temperature decreases by , in accord with an expectation for greater pressure sensitivity in lower-doped materials with lower . The peak magnetoresistance defined as decreases with increasing pressure as the metal - insulator transition becomes less abrupt. The influence of thermal expansion upon the resistivity is expected to be large.