Spin Fluctuations and the Pseudogap in Organic Superconductors

Abstract

We show that there are strong similarities in the spin lattice relaxation of non-magnetic organic charge transfer salts, and that these similarities can be understood in terms of spin fluctuations. Further, we show that, in all of the kappa-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 k-(BEDT-TTF)_2Cu[N(CN)_2]Br, k-(BEDT-TTF)_2Cu(NCS)_2, and k-(BEDT-TTF)_2Cu[N(CN)_2]Cl (under pressure) the pseudogap opens at the same temperature as coherence emerges in the (intralayer) transport. We argue that this is because the spin correlations are cut off 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 pressure). However, we find important differences in the metallic state of k-(BEDT-TTF)_2Cu_2(CN)_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 (TMTSF)_2ClO_4 is the same as superconducting critical temperature, which may be evidence that spin fluctuations mediate the superconductivity in the Bechgaard salts.

7 pages, 4 figures; to appear in PRB

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Cited by in corpus (14)

• Quantum frustration in organic Mott insulators: from spin liquids to unconventional superconductors
• Thermodynamics of a bad metal-Mott insulator transition in the presence of frustration
• Effective Coulomb interactions within BEDT-TTF dimers
• Pseudogap and singlet formation in cuprate and organic superconductors
• Mott transition, Widom line and pseudogap in the half-filled triangular lattice Hubbard model
• Dynamical reduction of the dimensionality of exchange interactions and the "spin-liquid" phase of $\kappa$-(BEDT-TTF)${}_{2}X$
• Anisotropy of electronic correlations: On the applicability of local theories to layered materials
• Quantum critical local spin dynamics near the Mott metal-insulator transition in infinite dimensions
• Stretched exponential spin relaxation in organic superconductors
• Antiferromagnetic fluctuations in the quasi-two-dimensional organic superconductor detected by Raman spectroscopy
• Quantum oscillations suggest hidden quantum phase transition in the cuprate superconductor Pr${}_2$CuO${}_{4\pm \delta }$
• Fate of the Hebel-Slichter peak in superconductors with strong antiferromagnetic fluctuations
• Hybridization-Controlled Pseudogap State in the Quantum Critical Superconductor CeCoIn5
• Superconducting fluctuations in organic molecular metals enhanced by Mott criticality