New pyrochlore iridate In₂Ir₂O₇ stabilised by high pressure

In 5d transition metal oxides Coulomb repulsion, crystal field splitting and spin-orbit coupling are comparable which leads to a variety of exotic electronic states. Pyrochlore iridates with chemical formula A₂Ir₂O₇ (A= Y, rare earth) consist of A and Ir corner-sharing tetrahedral networks and are predicted to exhibit Weyl semimetal or topological insulator states. Their properties depend on the ionic radius of A³⁺, where the system is driven from metallic to insulating regime with decreasing A³⁺ size. Those effects are likely related to diverging degree of local lattice distortion. In our work in order to explore small A³⁺ limit we synthesised new pyrochlore In₂Ir₂O₇ using high pressure. Structural analysis shows its octahedra are the most distorted among A₂Ir₂O₇ family which is in agreement with its insulating behaviour. It shows magnetic order at T_N = 55 K with θ_CW ∝ -400 K, which suggests strong frustration and is in large contrast with Y₂Ir₂O₇ (T_N = 155 K, θ_CW ∝ -130 K). Our band calculation shows that despite large distortion In₂Ir₂O₇ is in proximity to pure j_eff = 1/2, unlike Y₂Ir₂O₇, which shows strong hybridisation of j_eff = 1/2 and j_eff = 3/2. We will discuss the possible origin of almost pure j_eff = 1/2 state in In₂Ir₂O₇.