Real Space Imaging of the Metal–Insulator Phase Separation in the Band Width Controlled Organic Mott System κ-(BEDT-TTF)<sub>2</sub>Cu[N(CN)<sub>2</sub>]Br

Sasaki, T.; Yoneyama, N.; Suzuki, Ai; Kobayashi, Norio; Ikemoto, Yuka; Kimura, Hiroaki

doi:10.1143/jpsj.74.2351

Cited by 51 publications

(78 citation statements)

References 62 publications

(116 reference statements)

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“…In particular one needs to take care to account for the possible coexistence of metallic and insulating phases; this is expected as the Mott transition is first order in the organic charge-transfer salts. 62,63 The existence of a pseudogap has also been suggested in -͑BEDT-TSF͒ 2 GaCl 4 ͑Ref. 64͒ from microwave conductivity measurements.…”

Section: Open Problems and Future Experimentsmentioning

confidence: 91%

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

2007

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We give a quantitative analysis of the previously published nuclear magnetic resonance ͑NMR͒ experiments in the -͑ET͒ 2 X family of organic charge-transfer salts. The temperature dependence of the nuclear-spin relaxation rate 1 / T 1 , the Knight shift K s , and the Korringa ratio K is compared to the predictions of the phenomenological spin-fluctuation model of Moriya and Millis, Monien, and Pines ͑M-MMP͒, that has been used extensively to quantify antiferromagnetic spin fluctuations in the cuprates. For temperatures above T NMR Ӎ 50 K, the model gives a good quantitative description of the data in the metallic phases of several -͑ET͒ 2 X materials. These materials display antiferromagnetic correlation lengths which increase with decreasing temperature and grow to several lattice constants by T NMR . It is shown that the fact that the dimensionless Korringa ratio is much larger than unity is inconsistent with a broad class of theoretical models ͑such as dynamical mean-field theory͒ which neglects spatial correlations and/or vertex corrections. For materials close to the Mott insulating phase the nuclear-spin relaxation rate, the Knight shift, and the Korringa ratio all decrease significantly with decreasing temperature below T NMR . This cannot be described by the M-MMP model and the most natural explanation is that a pseudogap, similar to that observed in the underdoped cuprate superconductors, opens up in the density of states below T NMR . Such a pseudogap has recently been predicted to occur in the dimerized organic charge-transfer salts materials by the resonating valence bond ͑RVB͒ theory. We propose specific experiments on organic superconductors to elucidate these issues. For example, measurements to see if high magnetic fields or high pressures can be used to close the pseudogap would be extremely valuable.

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Section: Open Problems and Future Experimentsmentioning

confidence: 91%

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

2007

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“…This decrease may be due to the metalinsulator phase separation caused by the first-order Mott transition. 11,12,25 The metallic domains resulting from the phase separation become superconducting below H c2 and reduce the total resistivity of the dominant Mott insulator. Therefore, on the resistivity curves for samples with x ranging 0.5-0.8 under magnetic fields, the jumps in and the temperature hysteresis of the resistivity should be attributed to the Mott insulating domains, which are dominant in the bulk sample; moreover the decrease in the resistivity and its recovery by applying magnetic fields may be caused by the metallic/superconducting minor fragments.…”

Section: 818mentioning

confidence: 99%

Mott transition and superconductivity in the strongly correlated organic superconductorκ−(BEDT−TTF)2Cu[N(<

2008

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The magnetic field effect on the phase diagram of the organic Mott system κ-(BEDT-TTF)2Cu[N(CN)2]Br in which the bandwidth was tuned by the substitution of deuterated molecules was studied by means of the resistivity measurements performed in magnetic fields. The lower critical point of the first-order Mott transition, which ended on the upper critical field Hc2-temperature plane of the superconductivity, was determined experimentally in addition to the previously observed upper critical end point. The lower critical end point moved to a lower temperature with the suppression of Tc in magnetic fields and the Mott transition recognized so far as the S-shaped curve reached T = 0 when H > Hc2 in the end.PACS numbers: 74.70. Kn, 71.30.+h, 74.25.Dw Metal-insulator (MI) transitions have been one of the central issues in strongly correlated electron systems. Among the various types of MI transitions, the Mott transition is the most attractive phenomenon, which arises from an electron-electron interaction in a wide range of materials.1 Mott insulator derives from a large electrical Coulomb repulsion energy U with respect to the bandwidth W . Metal transitions can occur in two ways in a Mott insulator: one can change the strength of the interaction U/W , while maintaining the required bandfilling value and is referred to as a bandwidth-controlled Mott transition or one can introduce carriers with the required density, while maintaining U/W and is referred to as a band-filling-controlled Mott transition. The former case occurs, for example, in vanadium oxides and molecular conductors, while the latter occurs in high-T c cuprate superconductors.Organic charge transfer salts based on the donor molecule bis(ethylenedithio)-tetrathiafulvalene, abbreviated as BEDT-TTF or ET, have been recognized as a highly correlated electron system.2 Among them, κ-(ET) 2 X with X = Cu(NCS) 2 , Cu[N(CN) 2 ]Y (Y = Br and Cl), etc. has attracted considerable attention due to its strongly correlated quasi-two-dimensional electron system because the strong dimer structure consisting of two ET molecules makes the conduction band half filled.3,4 Furthermore, the softness of the lattice in molecular conductors enables us to easily modulate the bandwidth by applying small physical and chemical pressures, while maintaining the band-filling. Therefore, the κ-(ET) 2 X system has been considered to be one of the typical bandwidth-controlled Mott systems.The first-order Mott transition characterized by an Sshaped curve induces the correlated metal and superconductor phases from the Mott insulator phase by applying a small helium gas pressure or by the slight molecular substitution of the donor or anion molecules. 3,5,6,7,8 The relation and transitions among the various phases in the phase diagram have been studied extensively, both experimentally and theoretically. Several unique features have been found in association with the Mott transition. The first-order transition is terminated at T U cr ≃ 32- 40 K 6,8,9 , which is the upper critical end poin...

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“…[20,21,24,25,[55][56][57][58]. Such inhomogeneity may explain the anomalous behavior of the inplane conductivity in these materials [59].…”

Section: Some Experimental Factsmentioning

confidence: 99%

“…In table 4 we give the main parameters deduced from the experimental data of Sasaki et al [24]. − 1.…”

Section: The Case Of (Tmtsf)2clo4mentioning

confidence: 99%

“…In (TMTSF) 2 X, studies were focused particularly on the cooling rate induced disorder in (TMTSF) 2 ClO 4 [13][14][15] and disorder generated by the anion substitution in (TMTSF) 2 (ClO 4 ) 1−x (ReO 4 ) x [16][17][18][19]. In κ(ET) 2 X, disorder was introduced by rapid cooling [20][21][22][23], chemical substitution of donor or anion [24][25][26][27][28], X-ray and proton damage [28][29][30].…”

Section: Introductionmentioning

confidence: 99%

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Inhomogeneous superconductivity in organic conductors: the role of disorder and magnetic field

Haddad¹,

Charfi‐Kaddour²,

Pouget³

2011

J. Phys.: Condens. Matter

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Several experimental studies have shown the presence of spatially inhomogeneous phase coexistence of superconducting and non superconducting domains in low dimensional organic superconductors. The superconducting properties of these systems are found to be strongly dependent on the amount of disorder introduced in the sample regardless of its origin. The suppression of the superconducting transition temperature Tc shows clear discrepancy with the result expected from the Abrikosov-Gor'kov law giving the behavior of Tc with impurities. Based on the time dependent Ginzburg-Landau theory, we derive a model to account for the striking feature of Tc in organic superconductors for different types of disorder by considering the segregated texture of the system. We show that the calculated Tc quantitatively agrees with experiments. We also focus on the role of superconducting fluctuations on the upper critical fields Hc2 of layered superconductors showing slab structure where superconducting domains are sandwiched by non-superconducting regions. We found that Hc2 may be strongly enhanced by such fluctuations.

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Real Space Imaging of the Metal–Insulator Phase Separation in the Band Width Controlled Organic Mott System κ-(BEDT-TTF)₂Cu[N(CN)₂]Br

Cited by 51 publications

References 62 publications

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

Mott transition and superconductivity in the strongly correlated organic superconductorκ−(BEDT−TTF)2Cu[N(<

Inhomogeneous superconductivity in organic conductors: the role of disorder and magnetic field

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Real Space Imaging of the Metal–Insulator Phase Separation in the Band Width Controlled Organic Mott System κ-(BEDT-TTF)2Cu[N(CN)2]Br

Cited by 51 publications

References 62 publications

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

Antiferromagnetic spin fluctuations in the metallic phase of quasi-two-dimensional organic superconductors

Mott transition and superconductivity in the strongly correlated organic superconductorκ−(BEDT−TTF)2Cu[N(<

Inhomogeneous superconductivity in organic conductors: the role of disorder and magnetic field

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Real Space Imaging of the Metal–Insulator Phase Separation in the Band Width Controlled Organic Mott System κ-(BEDT-TTF)₂Cu[N(CN)₂]Br