Anomalous behaviour of the in-plane electrical conductivity of the layered superconductor  -(BEDT-TTF)<sub>2</sub>Cu(NCS)<sub>2</sub>

Singleton, John; Mielke, C. H.; Hayes, W.; Schlueter, John A.

doi:10.1088/0953-8984/15/12/103

Cited by 16 publications

(30 citation statements)

References 34 publications

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“…14 Local variations in crystal structure could lead to regions that are either predisposed to remain metallic or form an insulating state such as a density wave. 14,25 Additional support for this picture of coexisting "insulating" and "metallic" regions is given by the rather varied behavior of samples with nominally the same composition ͓see, e.g., Figs. 1͑a͒-1͑c͔͒, which could be explained by variations in the relative proportions of the two components.…”

Section: Resultsmentioning

confidence: 97%

“…A more likely scenario that could potentially lead to much the same resistivity behavior is the segregation of the sample into insulating and metallic-superconducting domains, 14,25 with the insulating regions ͑again, perhaps due to density-wave formation͒ forming at the characteristic temperature T MI . This mixture of phases may be the consequence of the mechanisms for intrinsic disorder, both static and dynamic, known to occur in the ␤Љ-͑BEDT-TTF͒ 4 ͓͑H 3 O͒M͑C 2 O 4 ͒ 3 ͔ · Y salts.…”

Section: Resultsmentioning

confidence: 99%

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Robust superconducting state in the low-quasiparticle-density organic metalsβ″−(BEDT−TTF)4[(
Bangura
¹
,
Coldea
²
,
Singleton
³

et al. 2005
Phys. Rev. B

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We report magnetotransport measurements on the quasi-two-dimensional charge-transfer salts ␤Љ-͑BEDT-TTF͒ 4 ͓͑H 3 O͒M͑C 2 O 4 ͒ 3 ͔Y, with Y =C 6 H 5 NO 2 and C 6 H 5 CN using magnetic fields of up to 45 T and temperatures down to 0.5 K. A surprisingly robust superconducting state with an in-plane upper critical field B c2ʈ Ϸ 33 T, comparable to the highest critical field of any BEDT-TTF superconductor, and critical temperature T c Ϸ 7 K is observed when M = Ga and Y =C 6 H 5 NO 2 . The presence of magnetic M ions reduces the in-plane upper critical field to Ϸ18 T for M = Cr and Y =C 6 H 5 NO 2 and M = Fe and Y =C 6 H 5 CN. Prominent Shubnikov-de Haas oscillations are observed at low temperatures and high magnetic fields, showing that the superconducting salts possess Fermi surfaces with one or two small quasi-two-dimensional pockets, their total area comprising Շ6% of the room-temperature Brillouin zone; the quasiparticle effective masses were found to be enhanced when the ion M was magnetic ͑Fe or Cr͒. The low effective masses and quasiparticle densities, and the systematic variation of the properties of the ␤Љ-͑BEDT-TTF͒ 4 ͓͑H 3 O͒M͑C 2 O 4 ͒ 3 ͔Y salts with unit-cell volume points to the possibility of a superconducting groundstate with a charge-fluctuation-mediated superconductivity mechanism such as that proposed by Merino and McKenzie ͓Phys. Rev. Lett. 87, 237002 ͑2001͔͒, rather than the spin-fluctuation mechanism appropriate for the -͑BEDT-TTF͒ 2 X salts.

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Robust superconducting state in the low-quasiparticle-density organic metalsβ″−(BEDT−TTF)4[(
Bangura
¹
,
Coldea
²
,
Singleton
³

et al. 2005
Phys. Rev. B

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“…The measurements in Figs. 1 and 2 use a well-characterized crystal also employed in Refs. [4,11,15]. Additional experiments (e.g.…”

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confidence: 99%

“…A T 2 scattering rate was inferred from B = 0 resistivity measurements [25]. However, problems in deconvolving the in-plane resistivity component ρ || from ρ zz in experimental data [9,15], and the influence of the broad superconducting transition on the Tdependence of the measured resistivity [9] mean that this attribution can not be considered conclusive. By contrast, the T -dependent AMROs provide an unambiguous gauge of the scattering rate of normal-state quasiparticles, allowing the mechanism to be definitively identified.…”

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confidence: 99%

Persistence to High Temperatures of Interlayer Coherence in an Organic Superconductor

et al. 2007

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The interlayer magnetoresistance ρzz of the organic metal κ-(BEDT-TTF)2Cu(NCS)2 is studied in fields of up to 45 T and at temperatures T from 0.5 K to 30 K. The peak in ρzz seen in inplane fields, a definitive signature of interlayer coherence, remains to T s exceeding the Anderson criterion for incoherent transport by a factor ∼ 30. Angle-dependent magnetoresistance oscillations are modeled using an approach based on field-induced quasiparticle paths on a 3D Fermi surface, to yield the T dependence of the scattering rate τ −1 . The results suggest that τ −1 does not vary strongly over the Fermi surface, and that it has a T 2 dependence due to electron-electron scattering.PACS numbers: 74.70. Kn, 71.20.Rv, 78.20.Ls The past two decades have seen a tremendous blossoming of interest in compounds that possess quasi-twodimensional (Q2D) electronic bandstructure; examples include crystalline organic metals [1,2,3,4], cuprates [5] and layered ruthenates [6]. These materials may be described by a tight-binding Hamiltonian in which the ratio of the interlayer transfer integral t ⊥ to the average intralayer transfer integral t || is ≪ 1 [1,2,3,4]. The question arises as to whether the interlayer charge transfer is coherent or incoherent in these materials, i.e. whether or not the Fermi surface (FS) is three dimensional (3D), extending in the interlayer direction. Various criteria for interlayer incoherence have been proposed, including [7] where T is the temperature. In this picture, thermal fluctuations "wipe out" details of the interlayer periodicity [7]. The consequent interlayer incoherence is used as a justification for a number of theories which are thought to be pivotal in the understanding of Q2D materials (see e.g. [7,8,9,10]). It is therefore important to test assertions such as Eq. 1. To this end, we have measured the magnetic-field-orientation dependence of the resistance of the organic metal κ-(BEDT-TTF) 2 Cu(NCS) 2 [9] using fields of up to 45 T and T s of up to 30 K (Fig. 1). This material was chosen because its FS is well known [9, 11] (see Fig. 2(c)), previous low-T experiments have shown that the interlayer transfer integral is t a = 0.065 ± 0.007 meV [11,12] and modest T s allow the inequality in Eq. 1 to be exceeded by orders of magnitude (t a /k B ≈ 0.5 K). Our data show that interlayer coherence survives to at least k B T > ∼ 30t a (c.f. Eq. 1). In addition, the results in this paper determine the low-T scattering rate τ −1 for the quasiparticles. Recent works stress that an understanding of the effects of the scattering mechanism in organic metals gives vital information about the mechanism for superconductivity [13,14]. Electrical contacts were made to single crystals (∼ 0.7 × 0.5 × 0.1 mm 3 ) of κ-(BEDT-TTF) 2 Cu(NCS) 2 using 12.5 µm Pt wire bonded by graphite paste; contact resistances were ∼ 10 Ω. Current and voltage terminals were arranged such that the measured resistance R zz is proportional to the interlayer component of the resistivity tensor, ρ zz [11]. The measurements in Figs. 1 and ...

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“…Notably, the precise meaning of lifetimes extracted from quantum oscillations in magnetotransport and from cyclotron resonance experiments is still a matter of discussion in the literature. 29,35,36,[39][40][41][42] If a lifetime determined from AMRO data using a relaxationtime approximation is to be usefully compared with those obtained elsewhere then its physical significance must be clarified. 11,27,39 Addressing this issue is the main purpose of this paper.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic scattering in angular-dependent magnetoresistance oscillations of quasi-two-dimensional and quasi-one-dimensional metals: Beyond the relaxation-time approximation

Smith

McKenzie

2008

Phys. Rev. B

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The electrical resistivity for a current moving perpendicular to layers ͑chains͒ in quasi-two-dimensional ͑2D͒ ͓quasi-one-dimensional ͑1D͔͒ metals under an applied magnetic field of varying orientation is studied using Boltzmann transport theory. We consider the simplest nontrivial quasi-2D and quasi-1D Fermi surfaces but allow for an arbitrary elastic collision integral ͑i.e., a scattering probability with arbitrary dependence on momentum transfer͒ and obtain an expression for the resistivity which generalizes that previously found using a single relaxation-time approximation. The dependence of the resistivity on the angle between the magnetic field and current changes depending on the momentum dependence of the scattering probability. So, whereas zero-field intralayer transport is sensitive only to the momentum-averaged scattering probability ͑the transport relaxation rate͒, the resistivity perpendicular to layers measured in a tilted magnetic field provides detailed information about the momentum-dependence of interlayer scattering. These results help us to clarify the meaning of the relaxation rate determined from fits of angular-dependent magnetoresistance oscillations ͑AM-ROs͒ experimental data to theoretical expressions. Furthermore, we suggest how AMRO might be used to probe the dominant scattering mechanism.

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Anomalous behaviour of the in-plane electrical conductivity of the layered superconductor -(BEDT-TTF)₂Cu(NCS)₂

Cited by 16 publications

References 34 publications

Robust superconducting state in the low-quasiparticle-density organic metalsβ″−(BEDT−TTF)4[(
Bangura
¹
,
Coldea
²
,
Singleton
³

et al. 2005
Phys. Rev. B

Robust superconducting state in the low-quasiparticle-density organic metalsβ″−(BEDT−TTF)4[(
Bangura
¹
,
Coldea
²
,
Singleton
³

et al. 2005
Phys. Rev. B

Persistence to High Temperatures of Interlayer Coherence in an Organic Superconductor

Anisotropic scattering in angular-dependent magnetoresistance oscillations of quasi-two-dimensional and quasi-one-dimensional metals: Beyond the relaxation-time approximation

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Anomalous behaviour of the in-plane electrical conductivity of the layered superconductor -(BEDT-TTF)2Cu(NCS)2

Cited by 16 publications

References 34 publications

Robust superconducting state in the low-quasiparticle-density organic metalsβ″−(BEDT−TTF)4[(Bangura1, Coldea2, Singleton3 et al. 2005Phys. Rev. B

Robust superconducting state in the low-quasiparticle-density organic metalsβ″−(BEDT−TTF)4[(Bangura1, Coldea2, Singleton3 et al. 2005Phys. Rev. B

Persistence to High Temperatures of Interlayer Coherence in an Organic Superconductor

Anisotropic scattering in angular-dependent magnetoresistance oscillations of quasi-two-dimensional and quasi-one-dimensional metals: Beyond the relaxation-time approximation

Contact Info

Product

Resources

About

Anomalous behaviour of the in-plane electrical conductivity of the layered superconductor -(BEDT-TTF)₂Cu(NCS)₂

Robust superconducting state in the low-quasiparticle-density organic metalsβ″−(BEDT−TTF)4[(
Bangura
¹
,
Coldea
²
,
Singleton
³

et al. 2005
Phys. Rev. B

Robust superconducting state in the low-quasiparticle-density organic metalsβ″−(BEDT−TTF)4[(
Bangura
¹
,
Coldea
²
,
Singleton
³

et al. 2005
Phys. Rev. B