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Title: Two-stage orbital order and dynamical spin frustration in KCuF3
Authors: Lee, J.C.T.
Yuan, S.
Lal, S.
Joe, Y.I.
Gan, Y.
Smadici, S.
Finkelstein, K.
Feng, Y.
Rusydi, A. 
Goldbart, P.M.
Lance Cooper, S.
Abbamonte, P.
Issue Date: Jan-2012
Citation: Lee, J.C.T.,Yuan, S.,Lal, S.,Joe, Y.I.,Gan, Y.,Smadici, S.,Finkelstein, K.,Feng, Y.,Rusydi, A.,Goldbart, P.M.,Lance Cooper, S.,Abbamonte, P. (2012-01). Two-stage orbital order and dynamical spin frustration in KCuF3. Nature Physics 8 (1) : 63-66. ScholarBank@NUS Repository.
Abstract: The orbital degree of freedom is integral to many exotic phenomenain condensed matter, including colossal magnetoresistance and unconventional superconductivity. The standard model of orbital physics is the Kugel-Khomskii model, which first explained the symmetry of orbital and magnetic order in KCuF 3 and has since been applied to virtually all orbitally active materials. Here we present Raman and X-ray scattering measurements showing that KCuF3 exhibits a previously unidentified structural phase transition at T=50K, involving rotations of the CuF6 octahedra. These rotations are quasi-ordered and exhibit glassy hysteresis, but serve to stabilize Néel spin order at T=39K. We propose an explanation for these effects by supplementing the Kugel-Khomskii model with a direct, orbital exchange term that is driven by a combination of electron-electron interactions and ligand distortions. The effect of this term is to create a near degeneracy that dynamically frustrates the spin subsystem but is lifted at low temperature by subdominant, orbital-lattice interactions. Our results suggest that direct orbital exchange may be crucial for the physics of many orbitally active materials, including manganites, ruthenates and the iron pnictides.
Source Title: Nature Physics
ISSN: 17452473
DOI: 10.1038/nphys2117
Appears in Collections:Staff Publications

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