Meier, J. P. (b. 1942)

Powell, Mark Allan

doi:10.5040/9781472549839.162

Cited by 4 publications

(13 citation statements)

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“…It has recently been shown 98 that the observed variation of T c and ρ 0 for alloy β-(BEDT-TTF) 2 (I 3 ) 1−x (IBr 2 ) x for small x predicted by ( 23) is consistent with the observations of Tokumoto et al 96 Note that this theory has no free parameters once the T c0 (this work and Forro et al 105 ) and t ⊥ (AMRO experiments 132 ) have been determined.…”

Section: Interlayer Transport Theorysupporting

confidence: 84%

Dependence of the superconducting transition temperature of organic molecular crystals on intrinsically nonmagnetic disorder: A signature of either unconventional superconductivity or the atypical formation of magnetic moments

Powell

McKenzie

2004

Phys. Rev. B

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We give a theoretical analysis of published experimental studies of the effects of impurities and disorder on the superconducting transition temperature, Tc, of the organic molecular crystals κ-(BEDT-TTF)2X (where X=Cu[N(CN)2]Br and Cu(NCS)2 and BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) and β-(BEDT-TTF)2X (for X=I3 and IBr2). The Abrikosov-Gorkov (AG) formula describes the suppression of Tc both by magnetic impurities in singlet superconductors, including s-wave superconductors and by non-magnetic impurities in a non-s-wave superconductor. We show that various sources of disorder (alloying anions, fast electron irradiation, disorder accidentally produced during fabrication and cooling rate induced disorder) lead to the suppression of Tc as described by the AG formula. This is confirmed by the excellent fit to the data, the fact that these materials are in the clean limit and the excellent agreement between the value of the interlayer hopping integral, t ⊥ , calculated from this fit and the value of t ⊥ found from angular-dependant magnetoresistance and quantum oscillation experiments. There are only two scenarios consistent with the current state of experimental knowledge. If the disorder induced by all of the four methods considered in this paper is, as seems most likely, non-magnetic then the pairing state cannot be s-wave. We show that published measurements of the cooling rate dependence of the magnetisation are inconsistent with paramagnetic impurities. Triplet pairing is ruled out by NMR and upper critical field experiments. Thus if the disorder is non-magnetic then this implies that l ≥ 2, in which case Occam's razor suggests that d-wave pairing is realised in both β-(BEDT-TTF)2X and κ-(BEDT-TTF)2X. However, particularly given the proximity of these materials to an antiferromagnetic Mott transition, it is possible that the disorder leads to the formation of local magnetic moments via some novel mechanism. Thus we conclude that either β-(BEDT-TTF)2X and κ-(BEDT-TTF)2X are d-wave superconductors or else they display a novel mechanism for the formation of localised moments, possibly related to the competition between the antiferromagnetic and superconducting grounds states. We suggest systematic experiments to differentiate between these two scenarios.

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Section: Interlayer Transport Theorysupporting

confidence: 84%

Dependence of the superconducting transition temperature of organic molecular crystals on intrinsically nonmagnetic disorder: A signature of either unconventional superconductivity or the atypical formation of magnetic moments

Powell

McKenzie

2004

Phys. Rev. B

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“…These effects have been studied in the extended Hubbard (t-J ′ -V -U ) 1 model on a square lattice [22,23]. The importance, for the superconducting state, of the fact that the actual lattice has a rather lower symmetry than the square lattice has also been stressed recently [24].…”

Section: Quarter Filled Charge Transfer Salts -The β ′′ and θ Phasesmentioning

confidence: 99%

“…Note that although we have introduced these ideas in the context of BCS theory the symmetry arguments that follow are based basic truths about quantum mechanics and do not depend on the details of the microscopic theory of superconductivity. Thus symmetry analyses are a powerful framework in which to understand the phenomenology of unconventional superconductors [7,24,78].…”

Section: Pairing Symmetry (Evidence For Additional Symmetry Breaking)mentioning

confidence: 99%

“…The organic charge transfer salts form orthorhombic, monoclinic and triclinic crystals. This can lead to important differences between their superconducting states [24,94]. Orthorhombic crystals such as κ-(ET) 2 Cu[N(CN) 2 ]Br (in which the highly conducting plane is the a-c plane) are described by the D 2h point group.…”

Section: Spatial Symmetry ('S-wave' Versus 'D-wave')mentioning

confidence: 99%

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Strong electronic correlations in superconducting organic charge transfer salts

Powell

McKenzie

2006

J. Phys.: Condens. Matter

176

278

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We review the role of strong electronic correlations in quasi-twodimensional organic charge transfer salts such as (BEDT-TTF)2X, (BETS)2Y and β ′ -[Pd(dmit)2]2Z. We begin by defining minimal models for these materials. It is necessary to identify two classes of material: the first class is strongly dimerised and is described by a half-filled Hubbard model; the second class is not strongly dimerised and is described by a quarter filled extended Hubbard model. We argue that these models capture the essential physics of these materials. We explore the phase diagram of the half-filled quasi-two-dimensional organic charge transfer salts, focusing on the metallic and superconducting phases. We review work showing that the metallic phase, which has both Fermi liquid and 'bad metal' regimes, is described both quantitatively and qualitatively by dynamical mean field theory (DMFT). The phenomenology of the superconducting state is still a matter of contention. We critically review the experimental situation, focusing on the key experimental results that may distinguish between rival theories of superconductivity, particularly probes of the pairing symmetry and measurements of the superfluid stiffness. We then discuss some strongly correlated theories of superconductivity, in particular, the resonating valence bond (RVB) theory of superconductivity. We conclude by discussing some of the major challenges currently facing the field. These include: parameterising minimal models; the evidence for a pseudogap from nuclear magnetic resonance (NMR) experiments; superconductors with low critical temperatures and extremely small superfluid stiffnesses; the possible spin-liquid states in κ-(ET)2Cu2(CN)3 and β ′ -[Pd(dmit)2]2Z; and the need for high quality large single crystals.

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“…It has been shown that conformational changes in the terminal ethylene groups of BEDT-TTF can lead to intrinsically non-magnetic disorder [6,7]. In both κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br and β-(BEDT-TTF) 2 I 3 this disorder has been shown to lead to a suppression of the superconducting critical temperature [7,8]. Understanding this phenomena and the details of the conformational change involved may therefore be important in identifying the pairing symmetry of the superconducting state of these materials [7].…”

mentioning

confidence: 99%