Peculiarities of spin and charge degrees of freedom in strongly correlated layered cobaltates

The layered cobaltate systems stand for the rare case of metallic quasi-2D triangular lattices at doping $x$. While $x$=0 corresponds to a half-filled scenario, $x$=1 marks the band-insulating limit. Surprisingly, the phase diagram displays especially for $x>$0.5 a rich competition between different spin-orderings as well as intriguing charge-ordering processes. Though already at high doping, strong electronic correlations are mainly responsible for the complex physics [1-4]. By means of combinations of band-structure techniques with many-body approaches it is shown that various cobaltate features may be tackled successfully. For instance the in-plane crossover from antiferromagnetic spin correlations towards the onset of ferromagnetism as well as charge ordering tendencies favoring an effective kagome lattice close to $x$=0.67 in agreement with experiment. The charge order also substantially effects the spectral and transport properties, giving rise to a specific low-energy scale susceptible to nonlocal correlations. \\[4pt] [1] F. Lechermann, Phys. Rev. Lett. 102, 046403 (2009).\\[0pt] [2] C. Piefke, L. Boehnke, A. Georges and F. Lechermann, Phys. Rev. B 82, 165118 (2010).\\[0pt] [3] L. Boehnke and F. Lechermann, arXiv:1012.5943.\\[0pt] [4] Oleg E. Peil, A. Georges and F. Lechermann, arXiv:1107.437