Letter | Published:

Fluctuating superconductivity in organic molecular metals close to the Mott transition

Nature volume 449, pages 584587 (04 October 2007) | Download Citation


On cooling through the transition temperature Tc of a conventional superconductor, an energy gap develops as the normal-state charge carriers form Cooper pairs; these pairs form a phase-coherent condensate that exhibits the well-known signatures of superconductivity: zero resistivity and the expulsion of magnetic flux (the Meissner effect1). However, in many unconventional superconductors, the formation of the energy gap is not coincident with the formation of the phase-coherent superfluid. Instead, at temperatures above the critical temperature a range of unusual properties, collectively known as ‘pseudogap phenomena’, are observed2. Here we argue that a key pseudogap phenomenon—fluctuating superconductivity occurring substantially above the transition temperature—could be induced by the proximity of a Mott-insulating state. The Mott-insulating state in the κ-(BEDT-TTF)2X organic molecular metals3,4,5 can be tuned, without doping, through superconductivity into a normal metallic state as a function of the parameter t/U, where t is the tight-binding transfer integral characterizing the metallic bandwidth and U is the on-site Coulomb repulsion. By exploiting a particularly sensitive probe of superconducting fluctuations, the vortex-Nernst effect, we find that a fluctuating regime develops as t/U decreases and the role of Coulomb correlations increases.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    Introduction to Superconductivity 2nd edn (Dover Publications, Mineola, New York, 2004)

  2. 2.

    & The pseudogap in high-temperature superconductors: an experimental survey. Rep. Prog. Phys. 62, 61–122 (1999)

  3. 3.

    , & Organic Superconductors 2nd edn (Springer, Berlin, 2006)

  4. 4.

    Similarities between organic and cuprate superconductors. Science 278, 820–821 (1997)

  5. 5.

    et al. Mott transition, antiferromagnetism, and unconventional superconductivity in layered organic superconductors. Phys. Rev. Lett. 85, 5420–5423 (2000)

  6. 6.

    Metal–insulator transition in κ-(ET)2X and (DCNQI)2M: Two contrasting manifestation of electron correlation. J. Phys. Soc. Jpn 75, 051007 (2006)

  7. 7.

    , , , & C-13 study of a quasi-2-dimensional organic superconductor κ-(ET)2Cu[N(CN)2]Br. Europhys. Lett. 28, 205–210 (1994)

  8. 8.

    & Strong electronic correlations in superconducting organic charge transfer salts. J. Phys. Condens. Matter 18, R827–R866 (2006)

  9. 9.

    et al. Magnetotransport studies of the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 under pressure: the relationship between carrier effective mass and critical temperature. J. Phys. Condens. Matter 6, 2911–2924 (1994)

  10. 10.

    , & Unconventional critical behaviour in a quasi-two-dimensional organic conductor. Nature 436, 534–537 (2005)

  11. 11.

    et al. From semiconductor-semiconductor transition (42 K) to the highest Tc organic superconductor, κ-(ET)2Cu[N(CN)2]Cl (Tc = 12.5 K)]. Inorg. Chem. 29, 3272–3274 (1990)

  12. 12.

    , , , & Vortex-like excitations and the onset of superconducting phase fluctuation in underdoped La2-xSrxCuO4. Nature 406, 486–488 (2000)

  13. 13.

    et al. High field phase diagram of cuprates derived from the Nernst effect. Phys. Rev. Lett. 88, 257003 (2002)

  14. 14.

    et al. Dependence of upper critical field and pairing strength on doping in cuprates. Science 299, 86–89 (2003)

  15. 15.

    , & Nernst effect in high-Tc superconductors. Phys. Rev. B 73, 024510 (2006)

  16. 16.

    The theory of the galvanomagnetic and thermomagnetic effects in metals. Proc. R. Soc. Lond. Ser. A 193, 484–512 (1948)

  17. 17.

    et al. Observation of the Nernst signal generated by fluctuating cooper pairs. Nature Phys. 2, 683–686 (2006)

  18. 18.

    et al. Anomalous Nernst effect in the mixed state of the two-band organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Br and κ-(BEDT-TTF)2Cu(NCS)2. Physica C 264, 261–267 (1996)

  19. 19.

    et al. Effect of irradiation-induced disorder on the conductivity and critical temperature of the organic superconductor κ-(BEDT-TTF)2Cu(SCN)2. Phys. Rev. Lett. 96, 177002 (2006)

  20. 20.

    et al. Low-temperature vortex liquid states induced by quantum fluctuations in the quasi-two-dimensional organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. Phys. Rev. B 66, 224513 (2002)

  21. 21.

    et al. Angle dependence of the upper critical field in the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 (BEDT-TTF ≡ bis(ethylene-dithio)tetrathiafulvalene). J. Phys. Condens. Matter 11, L477–L484 (1999)

  22. 22.

    et al. Low-temperature penetration depth of κ-(ET)2Cu[N(CN)2]Br and κ-(ET)2Cu(NCS)2. Phys. Rev. Lett. 83, 4172–4175 (1999)

  23. 23.

    , & Doping a Mott insulator: physics of high-temperature superconductivity. Rev. Mod. Phys. 78, 17–85 (2006)

  24. 24.

    & Importance of phase fluctuations in superconductors with small superfluid density. Nature 374, 434–437 (1995)

  25. 25.

    & On the relationship between the critical temperature and the London penetration depth in layered organic superconductors. J. Phys. Condens. Matter 16, L367–L373 (2004)

  26. 26.

    , , & Magnetic penetration depth of κ-(BEDT-TTF)2Cu[N(CN)2]Br, determined from the reversible magnetization. Phys. Rev. B 46, 5822–5825 (1992)

  27. 27.

    , , , & Pressure dependence of the magnetic penetration depth in κ-(BEDT-TTF)2Cu(NCS)2. Phys. Rev. B 64, 144514 (2001)

  28. 28.

    & Universal scaling relations in molecular superconductors. Phys. Rev. Lett. 94, 097006 (2005)

  29. 29.

    Quantum fluctuations in two-dimensional superconductors. Phys. Rev. B 24, 5063–5070 (1981)

  30. 30.

    The resonating valence bond state in La2CuO4 and superconductivity. Science 235, 1196–1198 (1987)

  31. 31.

    & Half-filled layered organic superconductors and the resonating-valence-bond theory of the Hubbard-Heisenberg model. Phys. Rev. Lett. 94, 047004 (2005)

  32. 32.

    , & Theory of gossamer and resonating valence bond superconductivity. Phys. Rev. B 71, 014508 (2005)

  33. 33.

    , & Gaussian superconducting fluctuations, thermal transport, and the Nernst effect. Phys. Rev. Lett. 89, 287001 (2002)

Download references


Work at Oxford is funded by the EPSRC. Work at Argonne National Laboratory is supported by the Office of Basic Energy Sciences, Division of Materials Science, US Department of Energy. A.A. is supported by the Royal Society. We thank J. M. Bhaseen, K. Burnett, P. M. Chaikin, J. T. Chalker, L. Forro, D. Jaksch, N. P. Ong and I. A. Walmsley for discussions.

Author information


  1. Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU, UK

    • Moon-Sun Nam
    • , Arzhang Ardavan
    •  & Stephen J. Blundell
  2. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

    • John A. Schlueter


  1. Search for Moon-Sun Nam in:

  2. Search for Arzhang Ardavan in:

  3. Search for Stephen J. Blundell in:

  4. Search for John A. Schlueter in:

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Arzhang Ardavan.

About this article

Publication history






Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.