TY - JOUR

T1 - Unusual Symmetries in the Kugel-Khomskii Hamiltonian

AU - Harris, A. B.

AU - Yildirim, Taner

AU - Aharony, Amnon

AU - Entin-Wohlman, Ora

AU - Korenblit, I. Ya

PY - 2003/8/21

Y1 - 2003/8/21

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=4744359655&partnerID=8YFLogxK

U2 - 10.1103/PhysRevLett.91.087206

DO - 10.1103/PhysRevLett.91.087206

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AN - SCOPUS:4744359655

SN - 0031-9007

VL - 91

JO - Physical Review Letters

JF - Physical Review Letters

IS - 8

ER -