Abstract
Theoretical studies recently predicted the condensation of spin-orbit excitons at momentum q=π in t42g spin-orbit coupled three-orbital Hubbard models at electronic density n=4. In parallel, experiments involving iridates with noninteger valence states for the Ir ions are starting to attract considerable attention. In this publication, using the density matrix renormalization group technique we present evidence for the existence of an excitonic condensate at n=3.5 in a one-dimensional Hubbard model with a degenerate t2g sector, when in the presence of spin-orbit coupling. At intermediate Hubbard U and spin-orbit λ couplings, we found an excitonic condensate at the unexpected momentum q=π/2 involving jeff=3/2,m=±1/2, and jeff=1/2,m=±1/2 bands in the triplet channel, coexisting with an also unexpected block magnetic order. We also present the entire λ vs U phase diagram, at a fixed and robust Hund coupling. Interestingly, this new “block excitonic phase” is present even at large values of λ, unlike the n=4 excitonic phase discussed before. Our computational study helps to understand and predict the possible magnetic phases of materials with d3.5 valence and robust spin-orbit coupling.
