Magnetic excitations of the gapped quantum spin dimer antiferromagnet Sr₃Cr₂O₈

dimers by the dominant antiferromagnetic intrabilayer coupling. The dimers are coupled three dimensionally by frustrated interdimer interactions. A structural distortion from hexagonal to monoclinic leads to orbital order and lifts the frustration giving rise to spatially anisotropic exchange interactions. We have grown large single crystals of Sr₃Cr₂O₈ and have performed DC susceptibility, high-field magnetization and inelastic neutron scattering measurements. The neutron scattering experiments reveal three gapped and dispersive singlet to triplet modes arising from the three twinned domains that form below the transition thus confirming the picture of orbital ordering. The exchange interactions are extracted by comparing the data to a random phase approximation model and the dimer coupling is found to be J₀ = 5.551(9) meV, while the ratio of interdimer to intradimer exchange constants is J´/J₀ = 0.64(2). The results are compared to those for other gapped magnets.