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arXiv · 0912.2334

Orbital order, stacking defects and spin-fluctuations in the $p$-electron molecular solid RbO$_2$

E. R. Ylvisaker·R. R. P. Singh·W. E. Pickett
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Abstract

We examine magnon and orbiton behavior in localized O$_2$ anti-bonding molecular $\pi^*$ orbitals using an effective Kugel-Khomskii Hamiltonian derived from a two band Hubbard model with hopping parameters taken from {\em ab initio} density functional calculations. The considerable difference between intraband and interband hoppings leads to a strong coupling between the spin wave dispersion and the orbital ground state, providing a straightforward way of experimentally determining the orbital ground state from the measured magnon dispersion. The near degeneracy of different orbital ordered states leads to stacking defects which further modulate spin-fluctuation spectra. Proliferation of orbital domains disrupts long-range magnetic order, thus causing a significant reduction in the observed N\'eel temperature.

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E. R. Ylvisaker, R. R. P. Singh, W. E. Pickett. 2009-12-11. Orbital order, stacking defects and spin-fluctuations in the $p$-electron molecular solid RbO$_2$. https://doi.org/10.1103/physrevb.81.180405

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