Pressure-induced insulating state in Ba_1-x R_x IrO₃ ( R=Gd, Eu) single crystals

BaIrO3 is an unusual insulator with coexistent weak ferromagnetism, charge- and spin-density waves. Dilute rare-earth doping (e.g., 4%) for Ba induces a metallic state whereas application of modest pressure (≤12.1 kbar) readily restores an insulating state characterized by a three order of magnitude increase in resistivity. Since pressure generally increases orbital overlap and broadens energy bands, a pressure-induced insulating state is not commonplace. The profoundly dissimilar responses of the ground state to light doping and low hydrostatic pressures signal an unusual, delicate interplay between structural and electronic degrees of freedom in BaIrO3.