English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We have analyzed the symmetry properties and the ground state of an orbitalHubbard model with two orbital flavors, describing a partly filledspin-polarized $e_g$ band on a cubic lattice, as in ferromagnetic manganites.We demonstrate that the off-diagonal hopping responsible for transitionsbetween $x^2-y^2$ and $3z^2-r^2$ orbitals, and the absence of SU(2) invariancein orbital space, have important implications. One finds that superexchangecontributes in all orbital ordered states, the Nagaoka theorem does not apply,and the kinetic energy is much enhanced as compared with the spin case.Therefore, orbital ordered states are harder to stabilize in the Hartree-Fockapproximation (HFA), and the onset of a uniform ferro-orbital polarization andantiferro-orbital instability are similar to each other, unlike in spin case.Next we formulate a cubic (gauge) invariant slave boson approach using theorbitals with complex coefficients. In the mean-field approximation it leads tothe renormalization of the kinetic energy, and provides a reliable estimate forthe ground state energy of the disordered state. Using this approach one findsthat the HFA fails qualitatively in the regime of large Coulomb repulsion$U\to\infty$ -- the orbital order is unstable, and instead a stronglycorrelated orbital liquid with disordered orbitals is realized at any electronfilling.

Orbital liquid in ferromagnetic manganites: The orbital Hubbard model for $e_g$ electrons