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Collective excitations in Na2IrO3.

Jun-Ichi Igarashi1, Tatsuya Nagao

  • 1Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan.

Journal of Physics. Condensed Matter : an Institute of Physics Journal
|December 20, 2015
PubMed
Summary

This study investigates collective excitations in Sodium Iridium Oxide (Na2IrO3) using an itinerant electron model. Findings reveal that suppressed direct d-d transfer is crucial for explaining its magnetic and excitonic excitation spectra.

Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Quantum Chemistry

Background:

  • Sodium Iridium Oxide (Na2IrO3) is a material exhibiting complex magnetic and electronic properties.
  • Understanding its collective excitations is key to elucidating its exotic phases.

Purpose of the Study:

  • To model and understand the collective excitations in Na2IrO3.
  • To investigate the role of electron transfer pathways and direct d-d transfer on its electronic structure and magnetic ordering.

Main Methods:

  • Utilized a multi-orbital tight-binding model on a honeycomb lattice.
  • Employed the Hartree-Fock approximation for energy calculations.
  • Applied the random phase approximation to evaluate density-density correlation functions.

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Main Results:

  • Weak direct d-d transfer leads to flat energy bands and zigzag spin order.
  • Collective excitations manifest as bound states, with magnetic excitations below 50 meV and excitonic excitations above 350 meV.
  • Larger direct d-d transfer values are inconsistent with observed ground state ordering and excitation spectra.

Conclusions:

  • The study supports the suppression of direct d-d transfer, possibly due to structural distortions, in Na2IrO3.
  • These findings align with experimental observations from resonant inelastic x-ray scattering.
  • The itinerant electron approach provides a valid framework for understanding Na2IrO3's excitation spectrum.