Theoretical investigation of excitonic magnetism in LaSrCoO 4 .

We use the LDA+U approach to search for possible ordered ground states of LaSrCoO4 . We find a staggered arrangement of magnetic multipoles to be stable over a broad range of Co 3d interaction parameters. This ordered state can be described as a spin-density-wave-type condensate of [Formula: see text] excitons carrying spin S  =  1. Further, we construct an effective strong-coupling model, calculate the exciton dispersion and investigate closing of the exciton gap, which marks the exciton condensation instability. Comparing the layered LaSrCoO4 with its pseudo cubic analog LaCoO3 , we find that for the same interaction parameters the excitonic gap is smaller (possibly vanishing) in the layered cobaltite.