Novel magnetic ground state in a fractional-valence-state iridate

The fractional or non-integer valence state in 3d and 4d transition metal oxides always gives rise to novel physics and multifunctional applications, such as charge order, magnetoelectric effect, and double exchange. The ground state becomes even more complex for 5d systems, as a result of the enhanced spin-orbit couplings. In this paper, experimental and theoretical studies are performed on La3Ir3O11, a new iridate with a non-1/2 fractional valence state (+4.33) for Ir ions and a three-dimensional strongly frustrated structure composed of edge-shared Ir2O10 dimers. Density functional theory calculations explain the spin-orbit driven Mott insulating transport, and show that the electronic state is neither Jeff=1/2 state nor J=0 state. Such a peculiar electronic state leads to a novel magnetic ground state, which hosts strong antiferromagnetic fluctuation yet without a long-range magnetic order. These behaviors are eventually demonstrated by our theoretical model beyond the simple Curie-Weiss law. Our work would shed new light on the studies of quantum spin liquid.