Simultaneous Metal-Insulator and Antiferromagnetic Transitions in Orthorhombic Perovskite Iridate Sr0.94Ir0.78O2.68 Single Crystals

TL;DR

This study investigates the orthorhombic perovskite Sr0.94Ir0.78O2.68, revealing a simultaneous antiferromagnetic and metal-insulator transition at 185 K, highlighting the sensitivity of its electronic state to lattice distortions.

Contribution

It demonstrates the first observation of concurrent AFM and MI transitions in SrIrO3 derivatives and emphasizes the impact of lattice distortions on ground state properties.

Findings

Simultaneous AFM and MI transitions at 185 K.

Extended linear resistivity up to 800 K in-plane.

Sign change in Hall resistivity below 40 K.

Abstract

The orthorhombic perovskite SrIrO3 is a semimetal, an intriguing exception in iridates where the strong spin-orbit interaction coupled with electron correlations tends to impose a novel insulating state. We report results of our investigation of bulk single-crystal Sr0.94Ir0.78O2.68 or Ir-deficient, orthorhombic perovskite SrIrO3. It retains the same crystal structure as stoichiometric SrIrO3 but exhibits a sharp, simultaneous antiferromagnetic (AFM) and metal-insulator (MI) transition at 185 K. Above it, the basal-plane resistivity features an extended regime of almost linear-temperature dependence up to 800 K but the strong electronic anisotropy renders an insulating behavior in the out-of-plane resistivity. The Hall resistivity undergoes an abrupt sign change and grows below 40 K, which along with the Sommerfeld constant of 20 mJ/mole K2 suggests a multiband effect. All results including our first-principles calculations underscore a delicacy of the metallic state in SrIrO3 that is in close proximity to an AFM insulating state. The contrasting ground states in isostructural Sr0.94Ir0.78O2.68 and SrIrO3 illustrate a critical role of even slight lattice distortions in rebalancing the ground state in the iridates. Finally, the observed simultaneous AFM and MI transitions reveal a direct correlation between the magnetic transition and formation of a charge gap in the iridate, which is conspicuously absent in Sr2IrO4.