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.

7 pages, 6 figures, extended version as published in PRB

References in corpus (8)

• The spin state transition in LaCoO${}_3$; revising a revision
• Electron correlation and Fermi surface topology of Na${}_x$CoO${}_2$
• Evidence of a single nonmagnetic Co3+ state in the Na1CoO2 cobaltate
• Complete d-Band Dispersion and the Mobile Fermion Scale in NaxCoO2
• Na Induced Correlations in Na${}_x$CoO${}_2$
• Quasiparticle coherence and the nature of the metal-insulator phase transition in Na${}_x$CoO${}_2$
• Magnetic properties of spin-orbital polarons in lightly doped cobaltates
• Direct observation of strong correlations near the band insulator regime of Bi misfit cobaltates

Cited by in corpus (1)

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