Unusual Symmetries in the Kugel-Khomskii Hamiltonian

A. B. Harris, Taner Yildirim, Amnon Aharony, Ora Entin-Wohlman, I. Ya Korenblit

Research output: Contribution to journalArticlepeer-review

43 Scopus citations

Abstract

The Kugel-Khomskii Hamiltonian for cubic titanates describes spin and orbital superexchange interactions between [Formula presented] ions having threefold degenerate [Formula presented] orbitals. Since orbitals do not couple along “inactive” axes, perpendicular to the orbital planes, the total number of electrons in [Formula presented] orbitals in any such plane and the corresponding total spin are both conserved. A Mermin-Wagner construction shows that there is no long-range spin ordering at nonzero temperatures. Inclusion of spin-orbit coupling allows such ordering, but even then the excitation spectrum is gapless due to a continuous symmetry. Thus, the observed order and gap require more symmetry breaking terms.

Original languageEnglish
JournalPhysical Review Letters
Volume91
Issue number8
DOIs
StatePublished - 21 Aug 2003

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