Electron-doped Sr$_{2}$IrO$_{4-\delta}$ $(0\leq \delta \leq 0.04)$: Evolution of a disordered J$_{eff}=1/2$ Mott insulator into an exotic metallic state

Stoichiometric Sr$_{2}$IrO$_{4}$ is a ferromagnetic J$_{eff} = 1/2$ Mott insulator driven by strong spin-orbit coupling. Introduction of very dilute oxygen vacancies into single-crystal Sr$_{2}$IrO$_{4-\delta}$ $(\delta < 0.04)$ leads to significant changes in lattice parameters and drives a number of intriguing phenomena such as insulator-to-metal transition at $T_{MI} \approx 105K$, anomalous non-Ohmic behavior and an abrupt current-induced transition in the resistivity. Highly-anisotropic resistivity of the samples continues to decrease by several orders of magnitude below $T_{MI}$ without saturation to a residual limit at the lowest temperature studied $T=1.8K$. The low-temperature metallic state exhibits two distinct regimes (separated at $T\approx 52K$) of switching in the non-linear $I-V$ characteristics. The novel behavior illustrates an exotic ground state and constitutes a new paradigm for device structures.