μSR studies of magnetic superconductors based on the BETS molecule

Pratt, F. L.; Blundell, Stephen J.; Marshall, I.M.; Lancaster, Tom; Lee, Stephen; Drew, Alan J.; Divakar, Ujjual; Matsui, Hiroshi; Toyota, Naoki

doi:10.1016/s0277-5387(03)00254-7

Cited by 20 publications

(33 citation statements)

References 16 publications

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“…This approximate scaling of T c with ρ 3/2 s , or equivalently λ −3 , in 2D organic superconductors was noted previously and discussed in terms of the 2D physics of layered superconductors [7,8,23]. However, it now appears that the scaling relations between T c , ρ s and σ 0 are more universal, encompassing examples of q1D and 3D molecular superconductors alongside the 2D systems.…”

Section: Label Materialssupporting

confidence: 71%

“…2.3(1) [7] 250 (25) . From this data it can be seen that 1/λ 2 exhibits a power law dependence on σ0 that is completely opposite to that of the molecular systems.…”

Section: Label Materialsmentioning

confidence: 99%

“…1(a) shows ρ s /c 2 (= ne 2 /m * ǫ 0 c 2 ) and T c derived from µSR measurements in the vortex state [5,6], plotted against σ 0 (T c ) in the highest conductivity direction for a series of molecular superconductors. The materials range from a highly anisotropic quasi-one-dimensional (q1D) organic superconductor ((TMTSF) 2 ClO 4 ), through systems of two-dimensional (2D) layered organic superconductors (BETS and ET salts) to examples of three-dimensional (3D) fulleride superconductors; full details are listed in Table 1 [7,8,9,10,11,12,13,14,15,16,17,18,19,20]. Note that the parameter values vary over several orders of magnitude, which is important for successful determination of scaling properties.…”

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confidence: 99%

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Universal scaling relations in molecular superconductors

Pratt

2006

Comptes Rendus. Chimie

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Scaling relations between the superconducting transition temperature Tc, the superfluid stiffness ρs and the normal state conductivity σ0(Tc) are identified within the class of molecular superconductors. These new scaling properties hold as Tc varies over two orders of magnitude for materials with differing dimensionality and contrasting molecular structure, and are dramatically different from the equivalent scaling properties observed within the family of cuprate superconductors. These scaling relations place strong constraints on theories for molecular superconductivity. PACS numbers: 76.75.+i, 74.25.Nf, 74.25.Fy, 74.70.Kn, 74.20.De Understanding the phenomenon of superconductivity, now observed in quite disparate systems, such as metallic elements, cuprates and molecular metals, involves searching for universal trends across different materials, which might provide pointers towards the underlying mechanisms. One such trend is the linear scaling between the superconducting transition temperature (T c ) and the superfluid stiffness (ρ s = c 2 /λ 2 , where λ is the London penetration depth), first identified by Uemura et al for the underdoped cuprates [1]. Recently, scaling relations between ρ s and the normal state conductivity σ 0 have also been suggested and a linear relation between ρ s and the product σ 0 (T c )T c was demonstrated for cuprates and some elemental superconductors [2]. Here we show that these specific linear scaling relations do not hold for molecular superconductors, but a different form of powerlaw scaling is found to link ρ s , σ 0 (T c ) and T c . These scaling properties hold as T c varies over several orders of magnitude for materials with differing dimensionality and contrasting molecular structure, and the scaling is dramatically different from that of the cuprates. Our findings have considerable implications for the theory of superconductivity in molecular systems.Molecular superconductors are generally regarded as members of the wider group of 'exotic' superconductors that have attracted much research effort in recent years. However, the number of different examples of molecular superconductors is now sufficiently large that systematic studies of their properties may be made independently of the other non-molecular exotic superconductors. A general feature of all these exotic superconductors is the large carrier scattering rate observed in the normal state [3] leading to a picture of them as 'bad metals' [4]. The scattering rate at temperatures near T c may have particular relevance for the superconductivity, since it is expected that similar carrier interaction mechanisms would be dominant in the normal state resistance and in the pairing of carriers that leads to the formation of the superconducting state. It is therefore useful to study the correlation between σ 0 (T c ) and superconducting parameters such as T c and ρ s . Fig. 1(a) shows ρ s /c 2 (= ne 2 /m * ǫ 0 c 2 ) and T c derived from µSR measurements in the vortex state [5,6], plotted against σ 0 (T c ) in the highest c...

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Section: Label Materialssupporting

confidence: 71%

“…2.3(1) [7] 250 (25) . From this data it can be seen that 1/λ 2 exhibits a power law dependence on σ0 that is completely opposite to that of the molecular systems.…”

Section: Label Materialsmentioning

confidence: 99%

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confidence: 99%

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Universal scaling relations in molecular superconductors

Pratt

2006

Comptes Rendus. Chimie

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“…The possibility of a quantum critical point somewhere in the vicinity of the pressure where the superconducting critical temperature goes to zero may have important consequences for the observation that the materials with the lowest superconducting critical temperatures have extremely small superfluid stiffnesses and are very different from BCS superconductors. 5,52 Finally, we sketch an explanation of the observed phase diagram ͑Fig. 4͒.…”

Section: High Pressuresmentioning

confidence: 99%

“…With some materials having superfluid stiffnesses ͑n s ϰ 1 / 2 ͒ that are an order of magnitude smaller than the prediction of BCS theory. 5,52 We are only aware of one NMR experiment at high pressures in these materials. Reference 29 reports data for -͑ET͒ 2 Cu͓N͑CN͒ 2 ͔Br at 3 kbar ͑which leads to T c Ӎ 3.8 K͒ ͑Ref.…”

Section: High Pressuresmentioning

confidence: 99%

Spin fluctuations and the pseudogap in organic superconductors

Powell¹,

Yusuf²,

McKenzie³

2009

Phys. Rev. B

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We show that there are strong similarities in the spin-lattice relaxation of nonmagnetic organic chargetransfer salts and that these similarities can be understood in terms of spin fluctuations. Further, we show that, in all of the -phase organic superconductors for which there is nuclear-magnetic-resonance data, the energy scale for the spin fluctuations coincides with the energy scale for the pseudogap. This suggests that the pseudogap is caused by short-range spin correlations. In the weakly frustrated metals -͑BEDT-TTF͒ 2 Cu͓N͑CN͒ 2 ͔Br, -͑BEDT-TTF͒ 2 Cu͑NCS͒ 2 , and -͑BEDT-TTF͒ 2 Cu͓N͑CN͒ 2 ͔Cl ͑under pressure͒ the pseudogap opens at the same temperature as coherence emerges in the ͑intralayer͒ transport. We argue that this is because the spin correlations are cutoff by the loss of intralayer coherence at high temperatures. We discuss what might happen to these two energy scales at high pressures, where the electronic correlations are weaker. In these weakly frustrated materials the data is well described by the chemical pressure hypothesis ͑that anion substitution is equivalent to hydrostatic pressure͒. However, we find important differences in the metallic state of -͑BEDT-TTF͒ 2 Cu 2 ͑CN͒ 3 , which is highly frustrated and displays a spin liquid-insulating phase. We also show that the characteristic temperature scale of the spin fluctuations in ͑TMTSF͒ 2 ClO 4 is the same as superconducting critical temperature, which may be evidence that spin fluctuations mediate the superconductivity in the Bechgaard salts.

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Muon spin rotation of organic compounds

Blundell

NMR-MRI, ΜSR and Mössbauer Spectroscopies in Molecular Magnets

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μSR studies of magnetic superconductors based on the BETS molecule

Cited by 20 publications

References 16 publications

Universal scaling relations in molecular superconductors

Universal scaling relations in molecular superconductors

Spin fluctuations and the pseudogap in organic superconductors

Muon spin rotation of organic compounds

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