Lattice-Driven Magnetoresistivity and Metal-Insulator Transition in Single-Layered Iridates

Sr2IrO4 exhibits a novel insulating state driven by spin-orbit interactions. We report two novel phenomena, namely a large magnetoresistivity in Sr2IrO4 that is extremely sensitive to the orientation of magnetic field but exhibits no apparent correlation with the magnetization, and a robust metallic state that is induced by dilute electron (La3+) or hole (K+) doping for Sr2+ ions in Sr2IrO4. Our structural, transport and magnetic data reveal that a strong spin-orbit interaction alters the balance between the competing energies so profoundly that (1) the spin degree of freedom alone is no longer a dominant force; (2) underlying transport properties delicately hinge on the Ir-O-Ir bond angle via a strong magnetoelastic coupling; and (3) a highly insulating state in Sr2IrO4 is proximate to a metallic state, and the transition is governed by lattice distortions. This work suggests that a novel class of lattice-driven electronic materials can be developed for applications.