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Electronic theory for itinerant in-plane magnetic fluctuations in Na$_x$CoO$_2$

M. M. Korshunov·I. Eremin·A. Shorikov·V. I. Anisimov
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Abstract

Starting from {\it ab-initio} band structure for Na$_x$CoO$_2$, we derive the single-electron energies and the effective tight-binding description for the $t_{2g}$ bands using a projection procedure. We find that due to the presence of the next-nearest-neighbor hoppings a local minimum in the electronic dispersion close to the $Γ$ point of the first Brillouin zone forms. Therefore, in addition to a large Fermi surface an electron pocket close to the $Γ$ point emerges at high doping concentrations. The latter yields the new scattering channel resulting in a peak structure of the itinerant magnetic susceptibility at small momenta. This indicates itinerant in-plane ferromagnetic state above certain critical concentration $x_m$, in agreement with neutron scattering data. Below $x_m$ the magnetic susceptibility shows a tendency towards the antiferromagnetic fluctuations. We estimate the value of $0.58 < x_m < 0.7$ within the rigid band model and within the Hubbard model with infinite on-site Coulomb repulsion consistent with the experimental phase diagram.

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M. M. Korshunov, I. Eremin, A. Shorikov, V. I. Anisimov. 2007-03-01. Electronic theory for itinerant in-plane magnetic fluctuations in Na$_x$CoO$_2$. https://doi.org/10.1134/s0021364006240040

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