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arXiv · 1408.2152

From Hubbard bands to spin-polaron excitations in the doped Mott material Na$_x$CoO$_2$

Aljoscha Wilhelm·Frank Lechermann·Hartmut Hafermann·Mikhail I. Katsnelson·Alexander I. Lichtenstein
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Abstract

We investigate the excitation spectrum of strongly correlated sodium cobaltate within a realistic many-body description beyond dynamical mean-field theory (DMFT). At lower doping around $x$=0.3, rather close to Mott-critical half-filling, the single-particle spectral function of Na$_x$CoO$_2$ displays an upper Hubbard band which is captured within DMFT. Momentum-dependent self-energy effects beyond DMFT become dominant at higher doping. Around a doping level of $x\sim 0.67$, the incoherent excitations give way to finite-energy spin-polaron excitations in close agreement with optics experiments. These excitations are a direct consequence of the formation of bound states between quasiparticles and paramagnons in the proximity to in-plane ferromagnetic ordering.

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Aljoscha Wilhelm, Frank Lechermann, Hartmut Hafermann, Mikhail I. Katsnelson, Alexander I. Lichtenstein. 2014-08-09. From Hubbard bands to spin-polaron excitations in the doped Mott material Na$_x$CoO$_2$. https://doi.org/10.1103/physrevb.91.155114

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