Instability of the J_eff= 1/2 insulating state in Sr_n+1Ir_nO_3n+1 (N = 1 and 2)

The most profound consequence of the spin-orbit interaction in layered iridates is the realization of a recently proposed J_eff= 1/2 insulating state, which explains novel insulating behavior observed in the Sr_n+1Ir_nO_3n+1 materials. We review the basic physical properties of layered iridates, including our recent transport and thermodynamic data for Sr_n+1Ir_nO_3n+1 (n = 1, 2). These results indicate the spin-orbit interaction vigorously competes with Coulomb interactions, non-cubic crystal electric field interactions, and the Hund’s rule coupling, which leads to states wiThexotic properties that are highly susceptible to small perturbations. The effects of chemical doping, application of pressure and magnetic field are emphasized; these perturbations are relatively weak, but capable of influencing the spin-orbit interaction and generating a rich phase diagram of strongly competing ground states.