733 research outputs found

    Nature of Possible Magnetic Phases in Frustrated Hyperkagome Iridate

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    Based on Kitaev-Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions, we studied nature of possible magnetic phases in frustrated hyperkagome iridate, Na4_4Ir3_{3}O8_8 (Na-438). Using Monte-Carlo simulation, we showed that the phase diagram is mostly covered by two competing magnetic ordered phases; Z2_2 symmetry breaking (SB) phase and Z6_6 SB phase, latter of which is stabilized by the classical order by disorder. These two phases are separated by a first order phase transition line with Z8_8-like symmetry. The critical nature at the Z6_6 SB ordering temperature is characterized by the 3D XY universality class, below which U(1) to Z6_6 crossover phenomena appears; the Z6_6 spin anisotropy becomes irrelevant in a length scale shorter than a crossover length Ξ›βˆ—\Lambda_* while becomes relevant otherwise. A possible phenomenology of polycrystalline Na-438 is discussed based on this crossover phenomena

    Chiral Topological Excitons in a Chern Band Insulator

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    A family of semiconductors called as Chern band insulator are shown to host exciton bands with non-zero topological Chern integers and chiral exciton edge modes. Using a prototypical two-band Chern insulator model, we calculate a cross-correlation function to obtain the exciton bands and their Chern integers. The lowest exciton band acquires Chern integers such as Β±1\pm 1 and Β±2\pm 2 in electronic Chern insulator phase. The non-trivial topology can be experimentally observed both by non-local optoelectronic response of exciton edge modes and by a phase shift in the cross-correlation response due to the bulk mode. Our result suggests that magnetically doped HgTe, InAs/GaSb quantum wells and (Bi,Sb)2Te3\text{(Bi,Sb)}_{2} \text{Te}_{3} thin film are promising candidates for a platform of topological excitonics.Comment: 5+ pages, 3 figures with supplemental material

    Magnetostatic wave analog of integer quantum Hall state in patterned magnetic films

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    A magnetostatic spin wave analog of integer quantum Hall (IQH) state is proposed in realistic patterned ferromagnetic thin films. Due to magnetic shape anisotropy, magnetic moments in a thin film lie within the plane, while all spin-wave excitations are fully gapped. Under an out-of-plane magnetic field, the film acquires a finite magnetization, where some of the gapped magnons become significantly softened near a saturation field. It is shown that, owing to a spin-orbit locking nature of the magnetic dipolar interaction, these soft spin-wave volume-mode bands become chiral volume-mode bands with finite topological Chern integers. A bulk-edge correspondence in IQH physics suggests that such volume-mode bands are accompanied by a chiral magnetostatic spin-wave edge mode. The existence of the edge mode is justified both by micromagnetic simulations and by band calculations based on a linearized Landau-Lifshitz equation. Employing intuitive physical arguments, we introduce proper tight-binding models for these soft volume-mode bands. Based on the tight-binding models, we further discuss possible applications to other systems such as magnetic ultrathin films with perpendicular magnetic anisotropy (PMA).Comment: 20 pages, 12 figure
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