Pairing Symmetry Competition in Organic Superconductors

Kuroki, Kazuhiko

doi:10.1143/jpsj.75.051013

Cited by 66 publications

(67 citation statements)

References 162 publications

(265 reference statements)

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“…In fact, the presence of such a distant interaction has also been pointed out theoretically [45][46][47]49] for quasi-one-dimensional organic compounds (TMTSF) 2 X in the context of coexisting 2k F spin and 2k F charge density waves [50,51] and spin triplet pairing superconductivity for a review e.g. [48,49], [52][53][54][55][56]. Quite recently, Tahara et al estimated the electron-electron interaction in κ-(BEDT-TTF) 2 X from a first principles calculation, and also obtained a long ranged interaction [57].…”

Section: Resultsmentioning

confidence: 90%

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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Section: Resultsmentioning

confidence: 90%

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

Kuroki

2009

Science and Technology of Advanced Materials

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“…[29][30][31][32] In this material, coexistence of 2k F SDW and 2k F CDW has been experimentally observed in the insulating phase sitting next to the superconducting phase in the pressure-temperature phase diagram. 46,47 This coexistence cannot be understood within a model that considers only the on-site U and the nearest neighbor repulsion V , and the effect of the second nearest neighbor repulsion V ′ is crucial, 27-29, 31, 33, 34 sharing similarity with the present case.…”

Section: Comparison With (Tmtsf) 2 Xmentioning

confidence: 80%

The Origin of the Charge Ordering and Its Relevance to Superconductivity in θ-(BEDT-TTF)₂X: The Effect of the Fermi Surface Nesting and the Distant Electron–Electron Interactions

Kuroki

2006

J. Phys. Soc. Jpn.

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The origin of the charge ordering in organic compounds θ-(BEDT-TTF)2X (X = M M ′ (SCN)4, M =Tl,Rb,Co, M ′ =Cs,Zn) is studied using an extended Hubbard model. Calculating the charge susceptibility within random phase approximation (RPA), we find that the (3 × 3) ∼ (3 × 4) charge ordering observed at relatively high temperatures can be considered as a consequence of a cooperation between the Fermi surface nesting, controlled by the hopping integral in the c direction, and the electron-electron interactions, where the distant (next nearest neighbor) interactions that have not been taken into account in most of the previous studies play an important role. Mean field analysis at T = 0 also supports the RPA results, and further shows that in the 3 × 3 charge ordered state, some portions of the Fermi surface remain ungapped and are nested with a nesting vector close to the modulation wave vector of the horizontal stripe ordering observed at low temperatures in X = M M ′ (SCN)4. We further study the possibility of superconductivity by taking into account the distant off-site repulsions and the band structure corresponding to X =I3, in which superconductivity is experimentally observed. We find that there is a close competition between dxy-wave-like singlet pairing and px+2y-wave-like triplet pairing due to a cooperation between the charge and the spin fluctuations. The present analysis provides a possible unified understanding of the experimental phase diagram of the θ-(BEDT-TTF)2X family, ranging from a charge ordered insulator to a superconductor.

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“…[2][3][4] One of the main challenges of present research activities remains the determination of the microscopic origin of the Cooper pairing, 5 an issue all the more interesting because of the accumulating evidences in favor of unconventional d-wave symmetry superconductivity at least for the quasi-one-dimensional (quasi-1D) Bechgaard salts. 6 In the latter salts, it has been proposed 7 that the d-wave Cooper pairing is achieved through spin-density-wave (SDW) fluctuations, which arise because of the close proximity of a SDW ground state.…”

Section: Introductionmentioning

confidence: 99%

Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

et al. 2013

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We present a detailed low-temperature investigation of the statics and dynamics of the anions and methyl groups in the organic conductors (TMTSF) 2 PF 6 and (TMTSF) 2 AsF 6 (TMTSF: tetramethyl-tetraselenafulvalene). The 4 K neutron-scattering structure refinement of the fully deuterated (TMTSF) 2 PF 6 -D12 salt allows locating precisely the methyl groups at 4 K. This structure is compared to the one of the fully hydrogenated (TMTSF) 2 PF 6 -H12 salt previously determined at the same temperature. Surprisingly, it is found that deuteration corresponds to the application of a negative pressure of 5 × 10 2 MPa to the H12 salt. Accurate measurements of the Bragg intensity show anomalous thermal variations at low temperature both in the deuterated PF 6 and AsF 6 salts. Two different thermal behaviors have been distinguished. Small Bragg-angle measurements reflect the presence of low-frequency modes at characteristic energies θ E = 8.3 K and θ E = 6.7 K for the PF 6 -D12 and AsF 6 -D12 salts, respectively. These modes correspond to the low-temperature methyl group motion. Large Bragg-angle measurements evidence an unexpected structural change around 55 K, which probably corresponds to the linkage of the anions to the methyl groups via the formation of F. . .D-CD 2 bonds observed in the 4 K structural refinement. Finally we show that the thermal expansion coefficient of (TMTSF) 2 PF 6 is dominated by the librational motion of the PF 6 units. We quantitatively analyze the low-temperature variation of the lattice expansion via the contribution of Einstein oscillators, which allows us to determine for the first time the characteristic frequency of the PF 6 librations: θ E ≈ 50 K and θ E = 76 K for the PF 6 -D12 and PF 6 -H12 salts, respectively.

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Pairing Symmetry Competition in Organic Superconductors

Cited by 66 publications

References 162 publications

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

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

The Origin of the Charge Ordering and Its Relevance to Superconductivity in θ-(BEDT-TTF)₂X: The Effect of the Fermi Surface Nesting and the Distant Electron–Electron Interactions

Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

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Pairing Symmetry Competition in Organic Superconductors

Cited by 66 publications

References 162 publications

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

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

The Origin of the Charge Ordering and Its Relevance to Superconductivity in θ-(BEDT-TTF)2X: The Effect of the Fermi Surface Nesting and the Distant Electron–Electron Interactions

Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

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

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

The Origin of the Charge Ordering and Its Relevance to Superconductivity in θ-(BEDT-TTF)₂X: The Effect of the Fermi Surface Nesting and the Distant Electron–Electron Interactions