<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">Ab</mml:mi><mml:mspace width="0.3em" /><mml:mi mathvariant="italic">initio</mml:mi></mml:math>evaluation of the local effective interactions in the superconducting compound<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">Na</mml:mi><mml:mn>0.35</mml:mn></mml:msub><mml:mi mathvariant="normal">Co</mml:mi><mml:msub><mml:mi mathvariant=

Landron, Sylvain; Lepetit, Marie-Bernadette

doi:10.1103/physrevb.74.184507

Cited by 45 publications

(48 citation statements)

References 32 publications

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“…The LDA value fit by Zhou et al is roughly ∆ = −10meV , and therefore the on-site orbital energies are nearly degenerate. Alternatively, quantum chemistry calculations [14] yield a value of 300meV , so one might anticipate −10meV ≤ ∆ ≤ 300meV .…”

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confidence: 99%

Quasiparticle Dispersion and Heat Capacity ofNa0.3CoO2: A Dynamical Mean-Field Theory Study

2007

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We use the dynamical mean-field theory (DMFT) to calculate the angle resolved photoemission spectrum (ARPES) and heat capacity for Na0.3CoO2. Both the traditional Hirsch-Fye Quantum Monte-Carlo technique and the newly developed continuous time quantum Monte-Carlo technique are used to solve the DMFT impurity problem. We show that the eg' hole pockets on the Fermi surface are suppressed as the on-site coulomb repulsion is increased. A quantitative comparison with ARPES experiments and bulk heat capacity measurements indicate that the on-site coulomb repulsion is large relative to the LDA bandwidth.The cobaltates have demonstrated a wide variety complex behavior. The Na rich region of the phase diagram displays various degrees of anomalous behavior, such as Curie-Weiss behavior near a band insulator[1], charge disproportionation [2], and non-Fermi-liquid behavior in the resistivity [1]. Alternatively, the Na poor region of the phase diagram appears to be a Fermi-liquid. The magnetic susceptibility displays Pauli behavior, the resistivity is roughly quadratic at low temperatures [1], and the system appears to be homogeneous [2]. Therefore, the Na poor region of the phase diagram seems like a natural starting point to attempt to explain the ARPES experiments and heat capacity measurements from a quantitative standpoint.In Na x CoO 2 , the cubic component of the oxygen crystal field splits the Co d manifold into a set of 3-fold t 2g orbitals and 2-fold e g orbitals, while the trigonal component will further split the t 2g orbitals into a 1g and e ′ g . The nominal valence of Co in this system will be 4 − x, so the Fermi-energy will fall within the t 2g manifold. The LDA band structure displays two degenerate eigenvalues and one non-degenerate eigenvalue at the Γ-point, corresponding to the e ′ g and a 1g eigenvectors. The splitting between the eigenvalues is roughly 1 eV with the e ′ g levels below the Fermi energy and the a 1g above. Despite this distinct splitting at the Γ-point, the on-site orbital energies are nearly degenerate. Additionally, the projected density-of-states (DOS) clearly show that the a 1g orbital character is strongest at the top and bottom of the band while the e ′ g is present through most of the energy range of the t 2g bands. The Fermi surface consists of a large a 1g pocket around the Γ-point and six small e ′ g satellite pockets [3].Several experimental ARPES studies have been performed for Na 0.3 CoO 2 [4,5,6,7]. A general caricature of the LDA bands can be seen in the ARPES. The most notable difference as compared to LDA is the significant narrowing of the bands, and the suppression of the e ′ g pockets below the Fermi energy. Two previous studies addressed the effect of correlations on the electronic structure for x = 0.3, and they reached completely opposite conclusions. Zhou et al performed Gutzwiller calculations for a three-band model corresponding to the LDA t 2g band structure [8]. Using an infinite on-site coulomb repulsion, they show that the quasi-particle bands are significant...

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confidence: 99%

Quasiparticle Dispersion and Heat Capacity ofNa0.3CoO2: A Dynamical Mean-Field Theory Study

2007

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“…Using instead an H eff derived from a multiband Co-O model H mb through a low-energy reduction procedure, 17 and the value = 315 meV obtained from quantum-chemistry configuration-interaction calculations, 18 these pockets are absent and the electronic dispersion near the Fermi energy agrees with experiment. 15 In this procedure, no LDA results were used.…”

Section: Introductionmentioning

confidence: 56%

“…20,21 Summarizing previous results, if is taken as a parameter, a positive has the effect of shrinking the pockets, and for large enough , the pockets disappear from the Fermi surface, reconciling theory with ARPES experiments. 12,13,15 A positive value has been obtained by quantum-chemistry methods 18 and a negative one is obtained fitting the LDA dispersion with H eff . 9,10 Thus the origin of the discrepancy between different methods and the actual value of remains a subject of interest.…”

Section: Introductionmentioning

confidence: 99%

Effect of covalency and interactions on the trigonal splitting in NaxCoO2

Aligia

2013

Phys. Rev. B

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We calculate the effective trigonal crystal field that splits the t 2g levels of effective models for Na x CoO 2 as the local symmetry around a Co ion is reduced from O h to D 3d . To this end, we solve numerically a CoO 6 cluster containing a Co ion with all 3d states and their interactions included, and its six nearest-neighbor O atoms, with the geometry of the system, in which the CoO 6 octahedron is compressed along a C 3 axis. We obtain ≈ 130 meV, with the sign that agrees with previous quantum chemistry calculations but disagrees with first-principles results in the local density approximation (LDA). We find that is very sensitive to a Coulomb parameter that controls the Hund coupling and charge distribution among the d orbitals. The origin of the discrepancy with LDA results is discussed.

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“…The chemical compression of the CoO 2 layers along the caxis direction yields the trigonal deformation of the CoO 6 octahedra, and the on-site t 2g -triplet states become splitted into the ground e ′ g and excited a 1g orbital states with the axially symmetric a 1g wave functions extended along the c-direction. 53 Then, to obtain the asymmetry of the local d-shells, one has to take into account transitions of the holes into their anisotropic e ′ g orbital states along with the a 1g orbitals. However, the ab-initio calculations for the cobaltates indicate that the energies ≈ 300 meV of these LS e ′ g -excitations of the holes 53 match the typical energy ≈ 250 − 300 meV of excitations of the Co 3+ ions from their spinless to HS e g -states in the transition metal oxides.…”

Section: Discussionmentioning

confidence: 99%

Origin of electron disproportionation in metallic sodium cobaltates

et al. 2016

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Recently the unusual metallic state with a substantially non-uniform distribution of a charge and magnetic density in CoO2 planes was found experimentally in the NaxCoO2 compound with x > 0.6. We have investigated an origin of such electron disproportionation in the lamellar sodium cobaltates by calculating the ion states as a function of a strength of the electron correlations in the d(Co)-shells within the GGA+U approximation for the system with a realistic crystal structure. It was found that the nonuniformity of spin and charge densities are induced by an ordering of the sodium cations and enhanced correlations. Two important magnetic states of cobalt lattice competing with each other at realistic values of the correlation parameter were found -low spin hexagons (LS) and higher spin kagome lattice (HS-KSL). In the heterogeneous metallic HS-KSL phase magnetic Co ions form a kagomé structure. In LS phase the kagomé pattern is decomposed into hexagons and Co ions possess minimal values of their spin. Coexistence of these states could explain the emergence of the disproportionation with the peculiar kagomé structure experimentally revealed in previous studies of the cobaltates.

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Abinitioevaluation of the local effective interactions in the superconducting compoundNa0.35Co

Cited by 45 publications

References 32 publications

Quasiparticle Dispersion and Heat Capacity ofNa0.3CoO2: A Dynamical Mean-Field Theory Study

Quasiparticle Dispersion and Heat Capacity ofNa0.3CoO2: A Dynamical Mean-Field Theory Study

Effect of covalency and interactions on the trigonal splitting in NaxCoO2

Origin of electron disproportionation in metallic sodium cobaltates

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