Lattice-driven magnetoresistivity and metal-insulator transition in single-layered iridates

Sr₂IrO₄ exhibits an insulating state driven by spin-orbit interactions. We report two 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 greatly that (1) the spin degree of freedom alone is no longer a dominant force, (2) the 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 that can be controlled via either the magnetic field or chemical doping.