Publication details

Unusual Electron Correlations in NaxCoO2 Due to the Spin-State Quasidegeneracy of Cobalt Ions



Year of publication 2008
Type Article in Periodical
Magazine / Source Progress of Theoretical Physics Supplement
MU Faculty or unit

Faculty of Science

Field Solid matter physics and magnetism
Keywords sodium cobaltates; superconductivity; electron correlations
Description Recent studies exposed many remarkable properties of layered cobaltates NaxCoO2. Surprisingly, many-body effects have been found to increase at sodium-rich compositions of NaxCoO2 where one expects a simple, nearly free motion of the dilute S=1/2 holes doped into a band insulator NaCoO2. Here we discuss the origin of enigmatic correlations that turn a doped NaCoO2 into a strongly correlated electronic system. A minimal model including orbital degeneracy is proposed and its predictions are discussed. The model is based on a key property of cobalt oxides - the spin-state quasidegeneracy of CoO6 octahedral complex - which has been known, e.g., in the context of an unusual physics of LaCoO3 compound. Another important ingredient of the model is the 90 Co-O-Co bonding in NaxCoO2 which allows nearest-neighbor t2g-eg hopping.
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