Frustrated Spin System inθ-(BEDT-TTF)2RbZn(SCN)4

Seo, Hitoshi; Fukuyama, Hidetoshi

doi:10.1143/jpsj.67.1848

Cited by 14 publications

(10 citation statements)

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“…32,33) As regards the 2D case, the importance of this V i,j has been clarified recently in a 1/4-filled transition metal oxide NaV 2 O 5 , where a similar interplay between U , V i,j and the dimerization is present, and its ground state is proposed to be a peculiar type of CO state due to this V i,j . 34) As for the organic systems, the calculations without V i,j for θ d -type structure predict the ground state to be Mott insulating state, 35) inconsistent with the existence of CO disclosed by the experiments mentioned above. Thus, studies including V i,j are needed to understand CO phenomena in the above 2D organic conductors, although CO itself has already been suggested in α-type structures from the Hartree-Fock calculations by KF.…”

Section: §1 Introductionmentioning

confidence: 83%

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Charge Ordering in Organic ET Compounds

2000

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The charge ordering phenomena in quasi two-dimensional 1/4-filled organic compounds (ET) 2 X (ET=BEDT-TTF) are investigated theoretically for the θ and α-type structures, based on the Hartree approximation for the extended Hubbard models with both on-site and intersite Coulomb interactions. It is found that charge ordered states of stripe-type are stabilized for the relevant values of Coulomb energies, while the spatial pattern of the stripes sensitively depends on the anisotropy of the models. By comparing the results of calculations with the experimental facts, where the effects of quantum fluctuation is incorporated by mapping the stripe-type charge ordered states to the S = 1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating phases of θ-(ET) 2 M M ′ (SCN) 4 and α-(ET) 2 I 3 are deduced. Furthermore, to obtain a unified view among the θ, α and κ-(ET) 2 X families, the stability of the charge ordered state in competition with the dimeric antiferromagnetic state viewed as the Mott insulating state, which is typically realized in κ-type compounds, and with the paramagnetic metallic state, is also pursued by extracting essential parameters.KEYWORDS: charge ordering, organic conductors, BEDT-TTF, extended Hubbard model, Hartree approxima-The family of quasi two-dimensional (2D) organic conductors (ET) 2 X (ET=BEDT-TTF) is known to exhibit a variety of interesting electronic properties. 1) Their structure consists of alternating layers of anionic X − with the closed shell, and cationic ET 1/2+ whose π-band is 3/4-filled(1/4-filled in terms of holes) if all the ET molecules are equivalent. The variety in physical properties reflects that of spatial arrangements of ET molecules in the layer, which are classified by greek characters such as κ, α, θ, β, etc., together with the rather strong mutual Coulomb interaction among π-electrons. 2) Theoretical studies of Kino and Fukuyama 3, 4, 5, 6) (KF) developed a systematic way to understand the diversity in their ground state properties by taking into account the explicit anisotropy of the transfer integrals between ET molecules for each compound, and by *

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Section: §1 Introductionmentioning

confidence: 83%

“…It can be seen there that when V is increased the charge pattern of energy difference (eV) energy t p3 , which is known to be stable for V = 0. 35) When V p /V c is varied, the solution which gives the lowest energy easily changes as in the case of θ-phase. In Fig.…”

Section: θ D -Typementioning

confidence: 99%

Charge Ordering in Organic ET Compounds

2000

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“…Moreover in a MF study on the Hubbard model for the other CO material θ-ET 2 RbZn(SCN) 4 , CO state is not even stabilized. 117 Following these works, V ij added to the Hubbard model retaining the full anisotropy in t ij , i.e., the EHM for ET 2 X on the anisotropic triangular lattice, has been introduced by Seo, 118 who discussed the CO states there based on the MF approximation. As in the quasi-1D systems discussed in § 2, the intersite Coulomb interaction is also crucial for CO in the quasi-2D materials.…”

Section: Direct Observation Of the Co Transition In Quasi-2dmentioning

confidence: 99%

Theoretical Aspects of Charge Ordering in Molecular Conductors

et al. 2006

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Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: El acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription (Received February 4, 2008) Theoretical studies on charge ordering phenomena in quarter-filled molecular (organic) conductors are reviewed. Extended Hubbard models including not only the on-site but also the inter-site Coulomb repulsion are constructed in a straightforward way from the crystal structures, which serve for individual study on each material as well as for their systematic understandings. In general the inter-site Coulomb interaction stabilizes Wigner crystal-type charge ordered states, where the charge localizes in an arranged manner avoiding each other, and can drive the system insulating. The variety in the lattice structures, represented by anisotropic networks in not only the electron hopping but also in the inter-site Coulomb repulsion, brings about diverse problems in low-dimensional strongly correlated systems. Competitions and/or co-existences between the charge ordered state and other states are discussed, such as metal, superconductor, and the dimer-type Mott insulating state which is another typical insulating state in molecular conductors. Interplay with magnetism, e.g., antiferromagnetic state and spin gapped state for example due to the spin-Peierls transition, is considered as well. Distinct situations are pointed out: influences of the coupling to the lattice degree of freedom and effects of geometrical frustration which exists in many molecular crystals. Some related topics, such as charge order in transition metal oxides and its role in new molecular conductors, are briefly remarked.

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“…Important progress in understanding the origin of the charge correlations in θ-(BEDT-TTF) 2 X was made by Seo, who included the nearest neighbor off-site repulsions V p and V c in the model Hamiltonian (see figure 2) [15] in addition to the on-site interaction U , which had already been considered in the seminal studies of organic conductors by Kino and Fukuyama [19] and Seo and Fukuyama [20]. Mori estimated the interaction parameters by directly calculating the Coulomb interaction using the highest occupied molecular orbitals of BEDT-TTF, neglecting the screening effect [21].…”

Section: Theoretical Modelmentioning

confidence: 99%

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X

Kuroki

2009

Science and Technology of Advanced Materials

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A review is given on the theoretical studies of charge correlations in θ-(BEDT-TTF) 2 X . Various studies show that within a purely electronic model on the θ-type lattice with on-site U and nearest neighbor V p and V c interactions, the diagonal stripe, c-axis three-fold, and the vertical stripe charge correlations are favored in the regime V p < V c , V p ∼ V c , and V p > V c , respectively. In the realistic parameter regime of V p ∼ V c , there is competition between the c-axis three fold state and diagonal stripe state. Since these are different from the experimentally observed a-axis three fold and the horizontal stripe charge correlations, additional effects have to be included in order to understand the experiments. The electron-lattice coupling, which tends to distort the lattice into the θ d -type, is found to favor the horizontal stripe state, suggesting that the occurrence of this stripe ordering in the actual materials may not be of purely electronic origin. On the other hand, distant electron-electron interactions have to be considered in order to understand the a-axis three fold correlation, whose wave vector is close to the nesting vector of the Fermi surface. These studies seem to suggest that the minimal model to understand the charge correlation in θ-(BEDT-TTF) 2 X may be more complicated than expected. Future problems regarding the competition between different types of charge correlations are discussed.

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Frustrated Spin System inθ-(BEDT-TTF)₂RbZn(SCN)₄

Cited by 14 publications

References 15 publications

Charge Ordering in Organic ET Compounds

Charge Ordering in Organic ET Compounds

Theoretical Aspects of Charge Ordering in Molecular Conductors

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X

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Frustrated Spin System inθ-(BEDT-TTF)2RbZn(SCN)4

Cited by 14 publications

References 15 publications

Charge Ordering in Organic ET Compounds

Charge Ordering in Organic ET Compounds

Theoretical Aspects of Charge Ordering in Molecular Conductors

Theoretical aspects of charge correlations in θ-(BEDT-TTF)2X

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Product

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Frustrated Spin System inθ-(BEDT-TTF)₂RbZn(SCN)₄

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X