Theory of Carrier Concentration-Dependent Electronic Behavior in Layered Cobaltates

Li, H.; Clay, R. Torsten; Mazumdar, S.

doi:10.1103/physrevlett.106.216401

Cited by 10 publications

(15 citation statements)

References 47 publications

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“…Layered cobaltates are unique in that ρ can be varied over a wide range by varying x . We have shown that the ρ ‐dependent electronic behavior of anhydrous Na x CoO 2 can be explained through an identical mechanism as in the CTS . In the hydrated superconducting Na‐cobaltate with

x = 0.35

, the water enters as H 3 O + ions, and the Co valence is set by both Na doping and the amount of H 3 O + .…”

Section: The Ubiquity Of Unconventional ρ=12 Superconductorsmentioning

confidence: 90%

The chemical physics of unconventional superconductivity

Mazumdar

Clay

2014

Int J of Quantum Chemistry

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Attempts to explain correlated-electron superconductivity (SC) have largely focused on the proximity of the superconducting state to antiferromagnetism. Yet, there exist many correlated-electron systems that exhibit insulatorsuperconducting transitions where the insulating state exhibits spatial broken symmetry different from antiferromagnetism. Here, we focus on a subset of such compounds which are seemingly very different in which specific chemical stoichiometries play a distinct role, and small deviations from stoichiometry can destroy SC. These superconducting materials share a unique carrier concentration, at which we show there is a stronger than usual tendency to form local spinsinglets. We posit that SC is a consequence of these pseudomolecules becoming mobile as was suggested by Schafroth a few years prior to the advent of the Bardeen-CooperSchrieffer (BCS) theory.

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x = 0.35

, the water enters as H 3 O + ions, and the Co valence is set by both Na doping and the amount of H 3 O + .…”

Section: The Ubiquity Of Unconventional ρ=12 Superconductorsmentioning

confidence: 90%

The chemical physics of unconventional superconductivity

Mazumdar

Clay

2014

Int J of Quantum Chemistry

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“…We have taken t > 0. Elsewhere we have argued that the U/jtj and V/jtj in the cobaltates are similar to that in the CTS [8]. With the exception of a few N e , the ground state is always in the lowest spin state (0(1/2) for N e ¼ even(odd)) for t > 0.…”

mentioning

confidence: 85%

Is there a common theme behind the correlated‐electron superconductivity in organic charge‐transfer solids, cobaltates, spinels, and fullerides?

Mazumdar

Clay

2012

Physica Status Solidi (b)

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We posit that there exist deep and fundamental relationships between the above seemingly very different materials. The carrier concentration-dependences of the electronic behavior in the conducting organic charge-transfer solids and layered cobaltates are very similar. These dependences can be explained within a single theoretical model, the extended Hubbard Hamiltonian with significant nearest neighbor Coulomb repulsion. Interestingly, superconductivity in the cobaltates seems to be restricted to bandfilling exactly or close to one-quarter, as in the organics. We show that dynamic JahnTeller effects and the resultant orbital ordering can lead to 1/4-filled band descriptions for both superconducting spinels and fullerides, which show evidence for both strong electronelectron and electron-phonon interactions. The orbital orderings in antiferromagnetic lattice-expanded bcc M 3 C 60 and the superconductor are different in our model. Strong correlations, quarter-filled band and lattice frustration are the common characteristics shared by these unusual superconductors.

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“…Note that previous works already showed the importance of nonlocal correlations [32,33]. From a 'molecular orbitals' viewpoint, the CDW transition is driven by orbital polarization: the intersite interaction drives the symmetric orbital |u towards half-filling (hence suscep- tible to a MIT), while the two asymmetric orbitals |d 1,2 are completely filled (with in total 5 = 3(1 + y) electrons in each EKL unit cell).…”

mentioning

confidence: 90%

Strong Correlations Enhanced by Charge Ordering in Highly Doped Cobaltates

2011

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We present an explanation for the puzzling spectral and transport properties of layered cobaltates close to the band-insulator limit, which relies on the key effect of charge ordering. Blocking a significant fraction of the lattice sites deeply modifies the electronic structure in a way that is shown to be quantitatively consistent with photoemission experiments. It also makes the system highly sensitive to interactions (especially to intersite ones), hence accounting for the strong correlations effects observed in this regime, such as the high effective mass and quasiparticle scattering rate. These conclusions are supported by a theoretical study of an extended Hubbard model with a realistic band structure on an effective kagomé lattice.The layered cobaltate metals are famous for their remarkable electronic properties [1], ranging from a large thermoelectric response [2] charge-ordering [3,4] and puzzling magnetic behavior, to superconductivity when intercalated with water [5]. Because of the universality of the physical properties throughout the cobaltate family, it is believed that most of these properties have their roots in the electronic structure of the CoO 2 layers. Those are formed of edge-sharing octahedra, with the Co ions forming a triangular lattice. Either alkali(-earth) metals (Na, Li, Ca etc., as in Na x CoO 2 ) or more complex building blocks (e.g. rocksalt BiO or SrO planes in misfit cobaltates [6]) separate the layers and serve as electron donors. Varying the composition of the intercalated compounds controls the doping x ∈ [0, 1], resulting in a nominal Co (4−x)+ (3d 5+x ) valence in the low-spin configuration within the t 2g manifold. The latter is split by the local trigonal symmetry into one a 1g and two e g states. Strong Coulomb interactions have been documented [7] to occur within this orbital subspace.

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Theory of Carrier Concentration-Dependent Electronic Behavior in Layered Cobaltates

Cited by 10 publications

References 47 publications

The chemical physics of unconventional superconductivity

The chemical physics of unconventional superconductivity

Is there a common theme behind the correlated‐electron superconductivity in organic charge‐transfer solids, cobaltates, spinels, and fullerides?

Strong Correlations Enhanced by Charge Ordering in Highly Doped Cobaltates

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