Ring-exchange interaction in doubly degenerate orbital system
Joji Nasu, and Sumio Ishihara
TL;DR
This paper investigates the ring-exchange interaction in a Mott insulator with doubly degenerate orbitals, revealing its role in destabilizing orbital order and inducing complex orbital states with suppressed moments.
Contribution
It derives the Hamiltonian for ring-exchange interactions in doubly degenerate orbitals and explores their effects on orbital and magnetic ordering.
Findings
Weak ring-exchange interaction destroys orbital order.
Long-range magnetic octupole order emerges.
Competition suppresses ordered moments.
Abstract
Ring-exchange (RE) interaction in Mott insulator with doubly degenerate orbitals is studied. Hamiltonian for the RE interaction is derived by the perturbational calculation. A remarkably weak RE interaction destroys the orbital order caused by the order-by-fluctuation mechanism in the nearest-neighbor exchange-interaction model. A long range order of magnetic octupole moment, i.e. complex orbital wave functions, appears. Competition between octupole and quadrupole interactions strongly suppresses ordered moments.
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