Doubly degenerate orbital system in honeycomb lattice

Implication of orbital state in layered iron oxide

J. Nasu, A. Nagano, Makoto Naka, S. Ishihara

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

We study a doubly degenerate orbital model on a honeycomb lattice. This is a model for orbital states in multiferroic layered iron oxides. The classical and quantum models are analyzed by spin-wave approximation, Monte Carlo simulation, and Lanczos method. A macroscopic number of degeneracy exists in the classical ground state. In the classical model, a peak in the specific heat appears at a temperature which is much lower than the mean-field ordering one. Below this temperature, the angle of orbital pseudospin is fixed, but conventional orbital orders are not suggested. The degeneracy in the ground state is partially lifted by thermal fluctuation. We suggest a role of zero-dimensional fluctuation in hexagons on a low-temperature orbital structure. Lifting of the degeneracy also occurs at zero temperature due to the quantum zero-point fluctuation. We show that the ground-state wave function is well represented by a linear combination of the states where a honeycomb lattice is covered by nearest-neighboring pairs of orbitals with the minimum bond energy.

Original languageEnglish
Article number024416
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume78
Issue number2
DOIs
Publication statusPublished - 2008 Jul 17
Externally publishedYes

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Iron oxides
iron oxides
Ground state
orbitals
Temperature
Spin waves
ground state
Wave functions
Specific heat
hexagons
magnons
temperature
ferric oxide
specific heat
wave functions
approximation
simulation

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Doubly degenerate orbital system in honeycomb lattice : Implication of orbital state in layered iron oxide. / Nasu, J.; Nagano, A.; Naka, Makoto; Ishihara, S.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 78, No. 2, 024416, 17.07.2008.

Research output: Contribution to journalArticle

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