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The spin one-half Mott insulator Sr2VO4 exhibits an enigmatic phase
transition at around 100 K, at which magnetic susceptibility shows a
sharp drop. However, the neutron scattering experiments were not able
to detect any long-range magnetic order.
We present a theory of this phase transition and argue that the order parameter responsible for a symmetry breaking has a composite nature and is a spin-orbital analog of a magnetic octupole. In this magnetically hidden order, the expectation values of the local spin and orbital moments both exactly vanish. We predict nontrivial magnetic and octupolar excitations above the ordered state, that can be detected by inelastic neutron and resonant X-ray scattering experiments. [1] G. Jackeli and G. Khaliullin, Phys. Rev. Lett. 103, 067205 (2009) |
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