title: Large spin-wave energy gap in the bilayer iridate Sr3Ir2O7: evidence for enhanced dipolar interactions near the mott metal-insulator transition.
abstract: Using resonant inelastic x-ray scattering, we observe in the bilayer iridate Sr3Ir2O7, a spin-orbit coupling driven magnetic insulator with a small charge gap, a magnon gap of ≈92 meV for both acoustic and optical branches. This exceptionally large magnon gap exceeds the total magnon bandwidth of ≈70 meV and implies a marked departure from the Heisenberg model, in stark contrast to the case of the single-layer iridate Sr2IrO4. Analyzing the origin of these observations, we find that the giant magnon gap results from bond-directional pseudodipolar interactions that are strongly enhanced near the metal-insulator transition boundary. This suggests that novel magnetism, such as that inspired by the Kitaev model built on the pseudodipolar interactions, may emerge in small charge-gap iridates.
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Jungho
authors.initials: J
authors.lastname: Kim
authors.forename: A H
authors.initials: AH
authors.lastname: Said
authors.forename: D
authors.initials: D
authors.lastname: Casa
authors.forename: M H
authors.initials: MH
authors.lastname: Upton
authors.forename: T
authors.initials: T
authors.lastname: Gog
authors.forename: M
authors.initials: M
authors.lastname: Daghofer
authors.forename: G
authors.initials: G
authors.lastname: Jackeli
authors.forename: J
authors.initials: J
authors.lastname: van den Brink
authors.forename: G
authors.initials: G
authors.lastname: Khaliullin
authors.forename: B J
authors.initials: BJ
authors.lastname: Kim