Anisotropic resistivity and thermopower of the organic superconductor (ET)<sub>2</sub>Cu[ N(CN)<sub>2</sub>] Br

Buravov, L. I.; Kushch, N.D.; Merzhanov, V. A.; Osherov, M. V.; Khomenko, A.G.; Yagubskii, Eduard B.

doi:10.1051/jp1:1992207

Cited by 39 publications

(37 citation statements)

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“…3b) crystals at different pressure values. For both samples, we find a pronounced maximum in dρ/dT at about the same temperature T max = 44 K in accor-dance with previous results on an HR crystal 21 . With increasing pressure, the maximum becomes reduced in size, rounded and shifted to higher temperatures.…”

Section: Methodssupporting

confidence: 90%

Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-two-dimensional organic superconductorκ−(BEDT−TTF)2Cu[N

et al. 2005

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Resistivity measurements have been performed on a low (LR)-and high (HR)-resistance variant of the κ-(BEDT-TTF)2Cu[N(CN)2]Br superconductor. While the HR sample was synthesized following the standard procedure, the LR crystal is a result of a somewhat modified synthesis route. According to their residual resistivities and residual resistivity ratios, the LR crystal is of distinctly superior quality. He-gas pressure was used to study the effect of hydrostatic pressure on the different transport regimes for both variants. The main results of these comparative investigations are (i) a significant part of the inelastic-scattering contribution, which causes the anomalous ρ(T ) maximum in standard HR crystals around 90 K, is sample dependent, i.e. extrinsic in nature, (ii) the abrupt change in ρ(T ) at T * ≈ 40 K from a strongly temperature-dependent behavior at T > T * to an only weakly T-dependent ρ(T ) at T < T * is unaffected by this scattering contribution and thus marks an independent property, most likely a second-order phase transition, (iii) both variants reveal a ρ(T) ∝ AT 2 dependence at low temperatures, i.e. for Tc ≤ T ≤ T0, although with strongly sample-dependent coefficients A and upper bounds for the T 2 behavior measured by T0. The latter result is inconsistent with the T 2 dependence originating from coherent Fermi-liquid excitations.

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Section: Methodssupporting

confidence: 90%

Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-two-dimensional organic superconductorκ−(BEDT−TTF)2Cu[N

et al. 2005

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“…In the following, it is expressed as κ-(ET) 2 X for an abbreviation. These compounds have quasi-two-dimensional electronic structures, which have been confirmed by the Shubnikov-de Haas experiments [ 123] and by the strong anisotropy in the electronic transport [ 124]. The conduction band is mainly constructed from ET molecules.…”

Section: Organic Superconductormentioning

confidence: 70%

Theory of superconductivity in strongly correlated electron systems

et al. 2003

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In this article we review essential natures of superconductivity in strongly correlated electron systems (SCES) from a universal point of view. First we summarize experimental results on SCES by focusing on typical materials such as cuprates, BEDT-TTF organic superconductors, and ruthenate Sr 2 RuO 4 . Experimental results on other important SCES, heavy-fermion systems, will be reviewed separately. The formalism to discuss superconducting properties of SCES is shown based on the Dyson-Gor'kov equations. Here two typical methods to evaluate the vertex function are introduced: One is the perturbation calculation up to the third-order terms with respect to electron correlation. Another is the fluctuationexchange (FLEX) method based on the Baym-Kadanoff conserving approximation. The results obtained by the FLEX method are in good agreement with those obtained by the perturbation calculation. In fact, a reasonable value of T c for spin-singlet d-wave superconductivity is successfully reproduced by using both methods for SCES such as cuprates and BEDT-TTF organic superconductors. As for Sr 2 RuO 4 exhibiting spin-triplet superconductivity, it is quite difficult to describe the superconducting transition by using the FLEX calculation. However, the superconductivity can be naturally explained by the perturbation calculation, since the third-order terms in the anomalous self-energy play the essential role to realize the triplet superconductivity. Another important purpose of this article is to review anomalous electronic properties of SCES near the Mott transition, since the nature of the normal state in SCES has been one of main issues to be discussed. Especially, we focus on pseudogap phenomena observed in under-doped cuprates and organic superconductors. A variety of scenarios to explain the pseudogap phenomena based on the superconducting and/or spin fluctuations are critically reviewed and examined in comparison with experimental results. According to the recent theory, superconducting fluctuations, inherent in the quasi-two-dimensional and strong-coupling superconductors, are the origin of the pseudogap formation. In these compounds, superconducting fluctuations induce a kind of resonance between the Fermi-liquid quasi-particle and the Cooper-pairing states. This resonance gives rise to a large damping effect of quasi-particles and reduces the spectral weight near the Fermi energy. We discuss the magnetic and transport properties as well as the single-particle spectra in the pseudogap state by the microscopic theory of the superconducting fluctuations. As for heavy-fermion superconductors, experimental results are reviewed and several theoretical analyses on the mechanism are provided based on the same viewpoint as explained above.

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“…In some of the materials the intralayer resistivity also has a maximum as a function of temperature, but at a higher temperature T ʈ max ϾT Ќ max . 2,4,5 An important question concerns how the interlayer transport is effected by the coherence ͑or existence͒ of quasiparticles within the layers. 6,7 Recent angle-resolved photoemission spectroscopy ͑ARPES͒ experiments on two different layered cobalt oxide compounds 6 found that peaks were only observed in the electronic spectral function ͑cor-responding to coherent quasiparticle excitations within the layers͒ below a temperature T coh that was comparable to T Ќ max .…”

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confidence: 99%

Indications of coherence-incoherence crossover in layered metallic transport

Lundin

McKenzie

2003

Phys. Rev. B

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For many strongly correlated metals with layered crystal structure the temperature dependence of the interlayer resistance is different to that of the intralayer resistance. We consider a small polaron model which exhibits this behavior, illustrating how the interlayer transport is related to the coherence of quasiparticles within the layers. Explicit results are also given for the electron spectral function, interlayer optical conductivity, and the interlayer magnetoresistance. All these quantities have two contributions: one coherent ͑domi-nant at low temperatures͒ and the other incoherent ͑dominant at high temperatures͒. DOI: 10.1103/PhysRevB.68.081101 PACS number͑s͒: 71.38.Ht, 72.90.ϩy Many of the most interesting strongly correlated electron materials have a layered crystal structure and highly anisotropic electronic properties. Examples include the cuprates, 1 colossal magnetoresistance materials, 2 organic molecular crystals, 3,4 strontium ruthenate, 5 and cobalt oxides. 6 One poorly understood property is that the resistivity perpendicular to the layers can have quite a different temperature dependence to that parallel to the layers.7 This is in contrast to what is expected for an anisotropic Fermi liquid: the parallel and perpendicular resistivities then have the same temperature dependence, being determined by the intralayer scattering rate ⌫(T). In many of these materials the interlayer resistivity is a nonmonotonic function of temperature with a maximum at some temperature T Ќ max . In some of the materials the intralayer resistivity also has a maximum as a function of temperature, but at a higher temperature T ʈ max ϾT Ќ max . 2,4,5 An important question concerns how the interlayer transport is effected by the coherence ͑or existence͒ of quasiparticles within the layers.6,7 Recent angle-resolved photoemission spectroscopy ͑ARPES͒ experiments on two different layered cobalt oxide compounds 6 found that peaks were only observed in the electronic spectral function ͑cor-responding to coherent quasiparticle excitations within the layers͒ below a temperature T coh that was comparable to T Ќ max . Although many theoretical papers have considered the problem of interlayer transport ͑see Ref. 8 and references therein͒ we are unaware of any theory which starts with a many-body Hamiltonian and produces the three temperature scales T coh , T Ќ max , and T ʈ max . 9,10In this Rapid Communication we consider a simple microscopic model which elucidates the connection between interlayer transport and the coherence of quasiparticles. We find that the interlayer conductivity has two contributions. The coherent ͑incoherent͒ contribution is characterized by the intralayer momentum of the quasiparticle being ͑not being͒ conserved in the interlayer tunneling process and is dominant at low ͑high͒ temperatures. We show that experimentally the two different contributions could be clearly distinguished at finite frequencies or in a magnetic field parallel to the layers. The model is a layered version of Holstein's molecu...

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Anisotropic resistivity and thermopower of the organic superconductor (ET)₂Cu[ N(CN)₂] Br

Cited by 39 publications

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Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-two-dimensional organic superconductorκ−(BEDT−TTF)2Cu[N

Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-two-dimensional organic superconductorκ−(BEDT−TTF)2Cu[N

Theory of superconductivity in strongly correlated electron systems

Indications of coherence-incoherence crossover in layered metallic transport

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Anisotropic resistivity and thermopower of the organic superconductor (ET)2Cu[ N(CN)2] Br

Cited by 39 publications

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Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-two-dimensional organic superconductorκ−(BEDT−TTF)2Cu[N

Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-two-dimensional organic superconductorκ−(BEDT−TTF)2Cu[N

Theory of superconductivity in strongly correlated electron systems

Indications of coherence-incoherence crossover in layered metallic transport

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Anisotropic resistivity and thermopower of the organic superconductor (ET)₂Cu[ N(CN)₂] Br