Metal-Insulator Transition and Collapse of Magnetic Order*

The spin-orbit-assisted Mott insulator Sr₃Ir₂O₇ undergoes a phase transition from an antiferromagnetic insulator into a paramagnetic metal via electron doping. We present the results of ab initio electronic structure calculations which identify the transition and provide insight into its origins. Our results describe both the paramagnetic metallic state and the antiferromagnetic insulating state. The charge gap and staggered magnetization are observed to decrease with increasing doping, and a metal-insulator phase transition occurs at an electron concentration corresponding to 4.8% substitution of Sr with La, in good agreement with experiment. We also describe the structural effects of La doping in Sr₃Ir₂O₇ as a competition between deformation-potential effects driven by electron doping and steric effects from the substitution of smaller La atoms. Curiously, our first-principles calculations fail to capture the low-temperature structural distortion reported in the metallic regime, supporting the notion that this distortion arises as a secondary manifestation of an unconventional electronic order parameter in this material.