Related papers: Successive Phase Transitions in Na_{0.5}CoO_{2} ba…

We investigate the electronic state of a CoO_2 plane in the layered cobalt oxides Na_xCoO_2 using the 11 band d-p model on a two-dimensional triangular lattice, where the tight-binding parameters are determined so as to fit the LDA band…

The electronic state in a CoO_2 plane of the layered cobalt oxides Na_{x}CoO_2 is investigated by using the 11 band d-p model on a two-dimensional triangular lattice, where the tight-binding parameters are determined so as to fit the LDA…

A multi-orbital model for a CoO_2-layer in Na_xCoO_2 is derived. In this model the kinetic energy for the degenerate t_2g-orbitals is given by indirect hopping over oxygen, leading naturally to the concept of four inter-penetrating Kagome…

We obtain the electronic states and structures of two-dimensional cobalt oxides, Na$_{x}$CoO$_{2}$ (x=0, 0.35, 0.5 and 0.75) by utilizing the full-potential linear muffin-tin orbitals (FP-LMTO) methods, from which some essential electronic…

We report a first-principles projector augmented wave (PAW) study on Na$_{0.5}$CoO$_2$. With the sodium ion ordered insulating phase being identified in experiments, pure density functional calculations fail to predict an insulating ground…

$^{59}$Co NMR experiments have been performed on single crystals of the layered cobaltate Na$_{x}$CoO$_{2}$ with x=0.77 which is an antiferromagnet with N\'eel temperature $T_{N}=22$~K. In this metallic phase six Co sites are resolved in…

We used quantum chemical ab initio methods to determine the effective parameters of Hubbard and $t-J$ models for the $\rm Na_{x}CoO_2$ compounds (x=0 and 0.5). As for the superconducting compound we found the $a_{1g}$ cobalt orbitals above…

Magnetism of layered cobaltites Na$_x$CoO$_2$ with $x$ = 0.6 and 0.9 has been investigated by a positive muon spin rotation and relaxation ($\mu^+$SR) spectroscopy together with magnetic susceptibility and specific heat measurements, using…

The metal-insulator transition of the quarter-filled Hubbard model on triangular lattice is studied at the mean field level. We find a quasi-one dimensional metallic state with a collinear magnetic order competes closely with an insulating…

Layered cobaltates embody novel realizations of correlated quantum matter on a spin-1/2 triangular lattice. We report a high-resolution systematic photoemission study of the insulating cobaltates (Na1/2CoO2 and K1/2CoO2). Observation of…

We report $^{23}$Na and $^{59}$Co nuclear magnetic (NMR) and quadrupolar resonance (NQR) studies for the $x=2/3$ phase of the lamellar oxide Na$_{x}$CoO$_{2}$, which allowed us to establish reliably the atomic order of the Na layers and…

On the example of TiO$_4$ layer (such as realized in Sr$_2$TiO$_4$) we study electronic structure of multi-band $d-p$ models describing transition metal perovskites. In agreement with the experiment, the studied system is predicted to be a…

The electronic structure of the CuO monolayer is investigated taking into account the intra- and interatomic Coulomb interactions on copper and oxygen atoms. Local Coulomb interactions and covalence effects are treated exactly when…

Effects of Coulomb correlation on LaOFeAs electronic structure have been investigated by LDA+DMFT(QMC) method. The calculation results show that LaOFeAs is in the regime of intermediate correlation strength with significant part of the…

The nature of electronic states due to strong correlation and geometric frustration on the triangular lattice is investigated in connection to the unconventional insulating state of Na$_x$CoO$_2$ at $x=0.5$. We study an extended Hubbard…

Using density functional theory calculations including an on-site Coulomb term, we explore electronic and possibly topologically nontrivial phases in $3d$ transition metal oxide honeycomb layers confined in the corundum structure…

The study of the strength of correlations in Na$_x$CoO$_2$ is extended to the x=0 end of the phase diagram where Mott insulating behavior has been widely anticipated. Inclusion of correlation as modeled by the LDA+U approach leads to a Mott…

The CoO$_{2}$ layers in sodium-cobaltates Na$_{x}$CoO$_{2}$ may be viewed as a spin $S=1/2$ triangular-lattice doped with charge carriers. The underlying physics of the cobaltates is very similar to that of the high $T_{c}$ cuprates. We…

The charge ordering transition in the layer compound NaV2O5 is studied by means of exact diagonalization methods for finite systems. The 2-leg ladders of the V-Trellis lattice are associated with one spin variable of the vanadium…

Using muon spin spectroscopy we have found that, for both Na$_x$CoO$_2$ (0.6 $\leq x \leq$ 0.9) and 3- and 4-layer cobaltites, a common low temperature magnetic state (which in some cases is manifest as an incommensurate spin density wave)…