DC and high-frequency conductivity of the organic metals -(BEDT-TTF)2SF5RSO3 (R=CH2CF2 and CHF)

Glied, M.; Yasin, S.; Kaiser, Stefan; Drichko, Natalia; Dressel, Martin; Wosnitza, J.; Schlueter, John A.; Gard, Gary L.

doi:10.1016/j.synthmet.2009.01.027

Cited by 8 publications

(6 citation statements)

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“…The observed splitting suggests that the system is tuned into a state with a charge disproportionantion ∆ρ ≈ 0.2e between neighboring lattice sites [27]. Nevertheless the compound stays metallic with only a slight change in the slope of d.c. resistivity temperature dependence below 200 K [28]. We interpret the result as a formation of a weak fluctuating CO.…”

Section: (A)]mentioning

confidence: 61%

Bandwidth Tuning Triggers Interplay of Charge Order and Superconductivity in Two-Dimensional Organic Materials

et al. 2010

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We observe charge-order fluctuations in the quasi-two-dimensional organic superconductor β ′′ -(BEDT-TTF)2SF5CH2CF2SO3 both by means of vibrational spectroscopy, locally probing the fluctuating charge order, and investigating the in-plane dynamical response by infrared reflectance specctroscopy. The decrease of effective electronic interaction in an isostructural metal suppresses both charge-order fluctuations and superconductivity, pointing on their interplay. We compare the results of our experiments with calculations on the extended Hubbard model. PACS numbers: 74.70.Kn, 74.25.Gz, 71.30.+h, 71.10.Hf From a naive point of view, superconducting and ordered insulating states are incompatible. This is true, for example, for the competition of charge-density wave and superconductivity [1], or stripes in cuprates [2,3]. However, experimental and theoretical studies on materials with strong electronic correlations suggest that fluctuations of an ordered state may mediate superconductivity. Prime candidates for this mechanism are magnetic order in heavy fermions [4,5] and high-temperature superconductors [6], incommensurate charge-density waves in dichalcogenides [7], or fluctuating charge order in quasitwo-dimensional organic conductors [8][9][10][11][12][13][14].In BEDT-TTF-based 1/4-filled conductors the ground state can be tuned by modifying effective electronic correlations via changing the bandwidth [15,16] (Fig. 1a): A charge-ordered insulating state is observed when the effective Coulomb repulsion is large enough [16][17][18][19][20], while compounds with weaker effective electronic correlations are metallic [21]. In the metallic state close to the metalinsulator phase boundary, charge fluctuations are observed [9,20,22], while the response of coherent carriers is still present. These experimental results are in agreement to calculations on the extended Hubbard model. It is the minimum model that can describe a metalinsulator transition in quasi-two-dimensional molecular conductors with 1/4-filled conduction band [7]. It takes into account the effective on-site U/t and inter-site V /t Coulomb repulsion, where t is the hopping integral related to the bandwidth. This model predicts that fluctuations of checker-board charge order (CO) can act as an attractive interaction of quasiparticles forming Cooper pairs and lead to a superconducting state [8,23]. In this Letter we present an experimental evidence for a bandwidth tuned CO fluctuations in the normal state of β ′′ family of quasi-2D organic conductors. We see an unambiguous relation between the presence of CO fluctuations and superconductivity and discuss its origin. The studied materials are layered compounds, where a slightly anisotropic quasi-two-dimensional conducting electronic system of the (ab) plane is created by the overlap of the neighboring BEDT-TTF (bis-(ethylenedithio)tetrathiafulvalene) molecules [24] (Fig. 1b). The bandwidth is tuned by changing the size of the anion, by so called 'chemical pressure'. β ′′ -(BEDT-TTF) 2 SF 5 CH 2 CF 2 SO 3 (...

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Section: (A)]mentioning

confidence: 61%

Bandwidth Tuning Triggers Interplay of Charge Order and Superconductivity in Two-Dimensional Organic Materials

et al. 2010

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“…By lowering T , the resistivity of β ′′ -SC exhibits a change in slope around 150 K, where the spectral signatures of a frozen CO clearly appear, and the fluctuations starts to slow down. In contrast, no anomalies are observed in the temperature-dependent resistivity of β ′′ -M. 27 As shown in Fig. 9, the optical conductivity within the ab plane contains three main features which are common to both salts: 15 • A broad band around 2000-3000 cm −1 , associated with site-to-site transitions within fluctuating CO patterns;…”

Section: Discussionmentioning

confidence: 92%

Charge-order fluctuations and superconductivity in two-dimensional organic metals

et al. 2014

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We report comprehensive Raman and infrared investigations of charge-order (CO) fluctuations in the organic metal β ′′ -(BEDT-TTF)2SF5CHFSO3 and superconductor β ′′ -(BEDT-TTF)2SF5CH2CF2SO3. The charge-sensitive vibrational bands are analyzed through an extension of the well-known Kubo model for the spectral signatures of an equilibrium between two states. At room temperature, both salts exhibit charge fluctuations between two differently charged molecular states with an exchange frequency of about 6 × 10 11 s −1 . The exchange rate of the metallic salt remains roughly constant down to 10 K, while in the superconductor the exchange velocity starts to decrease below 200 K, and a "frozen" charge-ordered state emerges, and coexists with the charge-order fluctuation state down to the superconducting temperature. These findings are confronted with other spectroscopic experiments, and a tentative phase diagram is proposed for the β ′′ BEDT-TTF quarter-filled salts.

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“…The question now arises, whether charge disproportionation is still present in the superconducting phase; in other words, is there a region where charge-order and superconductivity coexist? While the normal and superconducting states of β ′′ -SC and β ′′ -d 8 SC have been exhaustively studied 15,19,20,24,[28][29][30] , the interplay of charge order and superconductivity is still unexplored and the border region remains terra incognita. In analogy to superconductivity in the vicinity of a magnetically ordered phase, where a certain range of coexistence was identified 5,7 , one could imagine that also charge disproportionation and superconductivity appear simultaneously in a specific region of the phase diagram.…”

Section: B Charge Order and Superconductivitymentioning

confidence: 99%

Coexistence of charge order and superconductivity in β″−(BEDT−TTF)2SF5CH2<

et al. 2019

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In the all-organic paramagnetic correlated metal β ′′ -(BEDT-TTF)2SF5CH2CF2SO3 spin fluctuations can be ruled out as glue to superconductivity below Tc = 5.5 K. Instead, we demonstrate the coupling of charge degrees of freedom to the superconducting state, which occurs adjacent to a charge-ordered insulating phase. Comparison to isostructural β ′′ -(BEDT-TTF)2SF5RSO3 compounds reveals that superconductivity is suppressed when the system is tuned away from the insulator towards the metal; enhanced charge imbalance, on the other hand, leads to an increase in Tc suggesting an involvement of charge fluctuations. By locally probing the charge disproportionation through the superconducting transition, we discover slight modifications of the Fano coupling constant and intensity at Tc indicating the effect of the paired electrons on the molecular vibrations.

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DC and high-frequency conductivity of the organic metals -(BEDT-TTF)2SF5RSO3 (R=CH2CF2 and CHF)

Cited by 8 publications

References 44 publications

Bandwidth Tuning Triggers Interplay of Charge Order and Superconductivity in Two-Dimensional Organic Materials

Bandwidth Tuning Triggers Interplay of Charge Order and Superconductivity in Two-Dimensional Organic Materials

Charge-order fluctuations and superconductivity in two-dimensional organic metals

Coexistence of charge order and superconductivity in β″−(BEDT−TTF)2SF5CH2<

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