The origin of strong correlations and superconductivity in Na${}_x$CoO${}_2$

Abstract

We propose a minimal model resolving a puzzle of enigmatic correlations observed in sodium-rich Na${}_x$CoO${}_2$ where one expects a simple, free motion of the dilute $S=1/2$ holes doped into a band insulator NaCoO${}_2$. The model also predicts singlet superconductivity at experimentally observed compositions. The model is based on a key property of cobalt oxides -- the spin-state quasidegeneracy of CoO${}_6$ octahedral complex -- leading to an unusual physics of, {\it e.g.}, LaCoO${}_3$. We show that correlated hopping between $t_{2g}$ and $e_g$ states leads to the spin-polaron physics at $x\sim 1$, and to an extended s-wave pairing at larger doping when coherent fermionic bands are formed.

arXiv comment7 pages, 6 figures, extended version as published in PRB

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Cited by in corpus (9)

• New mechanism and exact theory of superconductivity from strong repulsive interaction
• Strong correlations enhanced by charge-ordering in highly doped cobaltates
• From Hubbard bands to spin-polaron excitations in the doped Mott material Na${}_x$CoO${}_2$
• Origin of the electron disproportionation in the metallic sodium cobaltates
• A possibility of high spin hole states in doped CoO${}_2$ layered systems
• Enhanced low energy fluctuations and increasing out-of-plane coherence in vacancy ordered NaxCoO2
• Ab-initio studying of spin states of sodium cobaltate Na${}_{2/3}$CoO${}_2$
• Superconductivity in the spin-state crossover materials: Nickelates with planar-coordinated low-spin Ni${}^{2+}$ ions
• Statistical fluxes and the Curie-Weiss metal state