Synthesis, superconductivity, X-ray structure and electronic band structure of λ-(BETS)2GaCl4

Montgomery, L. K.; Burgin, T.; Huffman, John C.; Ren, J.; Whangbo, Myung‐Hwan

doi:10.1016/0921-4534(94)90404-9

Cited by 34 publications

(33 citation statements)

References 18 publications

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“…Recall also that (TMTTF) 2 PF 6 , which is certainly on the 1D side of the 1D-2D boundary, is nonsuperconducting. In contrast, λ-BETS does become superconducting and that too at a T c that is considerably higher than that in the (TMTSF) 2 X, indicating what we believe to be strongly 2D character 86 . We believe that the solution to this puzzle lies in recognizing the ρ =1/2 character of the (BETS) 2 X.…”

mentioning

confidence: 82%

“…Magnetic susceptibility studies indicate absence of anisotropy in the susceptibility, and no spin-flop transition (signature of antiferromagnetism) was found down to 10 K, which is close to the maximum superconducting critical temperature T c (onset 7.5 K, and even higher in certain samples) 84 . The absence of the SDW is particularly perplexing here in view of the strong twodimensionality predicted within extended Hückel band calculations 86 . The lattice structures of the λ-(BETS) 2 GaBr z Cl 4−z are known 84 .…”

Section: E λ-(Bets)2gabrzcl4−z (Bets = Bedt-tsf)mentioning

confidence: 99%

“…These materials, discovered only recently [84][85][86] , are superconducting for 0 < z ≤ 0.8 and semiconducting for 0.8 < z < 2.0. Thus the proximity between a semiconducting and a superconducting state that characterizes the TMTSF and the BEDT-TTF is also a characteristic feature of the λ-BETS.…”

Section: E λ-(Bets)2gabrzcl4−z (Bets = Bedt-tsf)mentioning

confidence: 99%

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Bond-order and charge-density waves in the isotropic interacting two-dimensional quarter-filled band and the insulating state proximate to organic superconductivity

2000

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We report three surprising results regarding the nature of the spatial broken symmetries in the two-dimensional (2D), quarter-filled band with strong electron-electron interactions that provides a microscopic model of the 2:1 cationic organic charge transfer solids (CTS). First, in direct contradiction to the predictions of one-electron theory, we find a coexisting "bond-order and chargedensity wave" (BCDW) insulating ground state in the 2D rectangular lattice for all anisotropies, including the isotropic limit. Second, in contrast to the interacting half-filled band, which exhibits one singlet-to-antiferromagnet (AFM) transition as the interchain coupling is increased from zero, there occur in the interacting quarter-filled band two distinct transitions: a similar singlet-toantiferromagnet/spin-density wave (AFM/SDW) transition at small interchain coupling, giving rise to a bond-charge-spin density wave (BCSDW) state, followed by a second AFM/SDW-to-singlet transition at large interchain coupling. Third, we show that our conclusions remain unchanged if one assumes the conventional "effective 1/2-filled" lattice of dimer sites for the CTS: the dimer lattice unconditionally dimerizes again to give the same BCDW found in the quarter-filled band. We make detailed comparisons to recent experiments in the tetramethyl-tetrathiafulvalene (TMTTF), tetramethyl-tetraselenafulvalene (TMTSF), bisethylenedithio-tetrathiafulvalene (BEDT-TTF) and bisethylenedithio-tetraselenafulvalene (BETS)-based CTS. Our theory explains the mixed chargespin density waves observed in TMTSF and certain BEDT-TTF systems, as well as the absence of antiferromagnetism in the BETS-based systems. An important consequence of this work is the suggestion that organic superconductivity is related to the proximate Coulomb-induced BCDW, with the SDW that coexists for large anisotropies being also a consequence of the BCDW, rather than the driver of superconductivity. We point out that the BCDW and BCSDW states are analogous to four different classes of "paired" semiconductors that are obtained within certain models of exotic superconductivity. That all four of these models can in principle give rise to superconductivity in the weakly incommensurate regime provides further motivation for the notion that the BCDW may be driving the superconductivity in the organics.

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confidence: 82%

Section: E λ-(Bets)2gabrzcl4−z (Bets = Bedt-tsf)mentioning

confidence: 99%

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Bond-order and charge-density waves in the isotropic interacting two-dimensional quarter-filled band and the insulating state proximate to organic superconductivity

2000

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“…When the innermost four sulphur atoms of BEDT-TTF [1] are replaced by selenium to produce BETS (where BETS stands for bis(ethylenedithio)tetraselenafulvalene), electrocrystallization gives rise to a range of charge-transfer salts with notably different properties compared to their BEDT-TTF counterparts [10,11,12,13]. Salts of the λ-phase morphology are presently unique to the BETS series, and λ-(BETS) 2 GaCl 4 (T c ≈ 5 K) remains the only superconducting BETS charge-transfer salt found thus far [12,14].…”

Section: Background Informationmentioning

confidence: 99%

“…Salts of the λ-phase morphology are presently unique to the BETS series, and λ-(BETS) 2 GaCl 4 (T c ≈ 5 K) remains the only superconducting BETS charge-transfer salt found thus far [12,14].…”

Section: Background Informationmentioning

confidence: 99%

Superconducting properties and Fermi-surface topology of the quasi-two-dimensional organic superconductor λ-(BETS)₂GaCl₄(BETS≡bis(ethylene-dithio)tetraselenafulvalene)

Mielke

Singleton

Nam

et al. 2001

J. Phys.: Condens. Matter

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Abstract. The Fermi surface topology of the organic superconductor λ-(BETS) 2 GaCl 4 has been determined using the Shubnikov-de Haas and magnetic breakdown effects and angle-dependent magnetoresistance oscillations. The former experiments were carried out in pulsed fields of up to 60 T, whereas the latter employed quasistatic fields of up to 30 T. All of these data show that the Fermi-surface topology of λ-(BETS) 2 GaCl 4 is very similar to that of the most heavily-studied organic superconductor, κ-(BEDT-TTF) 2 Cu(NCS) 2 , except in one important respect; the interplane transfer integral in λ-(BETS) 2 GaCl 4 is a factor ∼ 5 larger than that in κ-(BEDT-TTF) 2 Cu(NCS) 2 . The increased three-dimensionality of λ-(BETS) 2 GaCl 4 is manifested in radiofrequency penetration-depth measurements, which show a clear dimensional crossover in the behaviour of H c2 (T ). The radiofrequency measurements have also been used to extract the Labusch parameter determining the fluxoid interactions as a function of temperature, and to map the flux-lattice melting curve.

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λ‐Type BETS salts containing a mixed halide gallium anion, GaX_x Y_4−x^⊖ [X, Y = F, Cl, Br; BETS = Bis(ethylenedithio)tetraselenafulvalene]

et al. 1996

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Since the discovery of the first organic superconductor TMTSF2PF6, ['] the number of organic superconductors has rapidly increased. However, the mechanism of superconducting transition is still unclear. Therefore, the design of new organic superconductors with enhanced T, is very difficult. In order to break through this difficulty, the development of new types of conductors which permit systematic studies of superconducting behavior in organic systems is highly desirable. The discovery of a series of P-type ET superconductors (ET = Bis(ethy1enedithio)tetrathiafulvalene) indicated the correlation between T, (the superconducting transition temperature) and the unit cell volume, which can be altered by using various anions of different sizes.12] Similar correlations have been found in analogous ET superconductor^.^^^ Some K-type organic superconductors with a value of T, around 10 K have the characteristic broad resistivity-maximum above Tc, which indicates that the metallic nature of K-type organic superconductor is not simple. However, the depression of T, at high pressure can be easily explained. With increasing pressure, the intermolecular overlap of molecular orbitals becomes greater, and increasing the band width causes the state densities of the Fermi surface (D(+)) to decrease. Thus, it may be supposed that altering the cell volume via a change in anion size can control the band width, and produces the same effect as applying pressure. Increasing cell volume implies applying "negative pressure", enhancing the value of T,. A very attractive goal would be to find a way to control T, by modifying molecular structures and packings. Bis(ethy1enedithio)tetraselenafulvalene(BETS, see Fig. 1) and tetrahedral monoanions MX4@ (M = Ga, Fe, In; X = C1, Br) have produced many highly conductive comp o u n d~. '~~ One is an organic superconductor h-BETS*-GaCl4.l5] Isostructural h-BETS2FeC14 exhibits a sharp MI (Metal-Insulator) transition around 8 K, where a magnetic

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Synthesis, superconductivity, X-ray structure and electronic band structure of λ-(BETS)2GaCl4

Cited by 34 publications

References 18 publications

Bond-order and charge-density waves in the isotropic interacting two-dimensional quarter-filled band and the insulating state proximate to organic superconductivity

Bond-order and charge-density waves in the isotropic interacting two-dimensional quarter-filled band and the insulating state proximate to organic superconductivity

Superconducting properties and Fermi-surface topology of the quasi-two-dimensional organic superconductor λ-(BETS)₂GaCl₄(BETS≡bis(ethylene-dithio)tetraselenafulvalene)

λ‐Type BETS salts containing a mixed halide gallium anion, GaX_x Y_4−x^⊖ [X, Y = F, Cl, Br; BETS = Bis(ethylenedithio)tetraselenafulvalene]

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Synthesis, superconductivity, X-ray structure and electronic band structure of λ-(BETS)2GaCl4

Cited by 34 publications

References 18 publications

Bond-order and charge-density waves in the isotropic interacting two-dimensional quarter-filled band and the insulating state proximate to organic superconductivity

Bond-order and charge-density waves in the isotropic interacting two-dimensional quarter-filled band and the insulating state proximate to organic superconductivity

Superconducting properties and Fermi-surface topology of the quasi-two-dimensional organic superconductor λ-(BETS)2GaCl4(BETS≡bis(ethylene-dithio)tetraselenafulvalene)

λ‐Type BETS salts containing a mixed halide gallium anion, GaXx Y4−x⊖ [X, Y = F, Cl, Br; BETS = Bis(ethylenedithio)tetraselenafulvalene]

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Superconducting properties and Fermi-surface topology of the quasi-two-dimensional organic superconductor λ-(BETS)₂GaCl₄(BETS≡bis(ethylene-dithio)tetraselenafulvalene)

λ‐Type BETS salts containing a mixed halide gallium anion, GaX_x Y_4−x^⊖ [X, Y = F, Cl, Br; BETS = Bis(ethylenedithio)tetraselenafulvalene]