Possible effects of charge frustration inNaxCoO2: Bandwidth suppression, charge orders, and resurrected resonating valence bond superconductivity

Abstract

Charge frustration due to further neighbor Coulomb repulsion can have dramatic effects on the electronic properties of NaxCoO2 in the full doping range. It can significantly reduce the effective mobility of the charge carriers, leading to a low degeneracy temperature ǫF T . Such strongly renormalized Fermi liquid has rather unusual properties-from the point of view of the ordinary metals with ǫF ≫ T -but similar to the properties that are actually observed in the NaxCoO2 system. For example, we show that the anomalous thermopower and Hall effect observed in Na0.7CoO2 may be interpreted along these lines. If the repulsion is strong, it can also lead to charge order; nevertheless, away from the commensurate dopings, the configurational constraints allow some mobility for the charge carriers, i.e., there remains some "metallic" component. Finally, the particularly strong bandwidth suppression around the commensurate x = 1/3 can help resurrect the RVB superconductivity, which would otherwise not be expected near this high doping. These suggestions are demonstrated specifically for a tJ-like model with an additional nearest neighbor repulsion.

Sodium vacancy ordering and the co-existence of localized spins and itinerant charges in NaxCoO2

“…The Hall constant R H is predicted to be linear in T > T F , a special consequence of hopping on a triangular lattice. [22] Experimentally R H is linear in T above ∼ 100 K, and saturates to a very small value at low temperature. [2] The latter may be a consequence of cancellations between the small electron and hole pocket mentioned earlier.…”

High‐Temperature Electrical Transport and Thermoelectric Power of Partially Substituted Ca3Co4O9‐Based Ceramics

“…The large thermoelectric power is mainly related to spin degeneracy, electronic structure, and charge frustration in the vicinity of a Mott metal-insulator transition. 5 It is well known that Ca 3 Co 4 O 9 is a misfit-layered oxide, which consists of alternating layers of a distorted CaO-CoO-CaO rock-salt-type layer and a CdI 2 -type CoO 2 layer stacked in the c-axis direction. 6,7 These two layers have similar lattice parameters, i.e., a, c, and b, but different b lattice parameters.…”

From Hubbard bands to spin-polaron excitations in the doped Mott materialNaxCoO2

“…Several works have shown [15,[20][21][22][23] that, due to the t 2g filling and trigonal crystal-field effects, the bulk of the essential cobaltate physics may be described already within an interacting effective one-band model of dominant a 1g character. Charge self-consistent combined density functional theory and DMFT calculations within a three-band model confirm the validity of the single-band treatment: At x = 0.3, the e g -like hole pockets are suppressed.…”