Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Fluctuating superconductivity in organic molecular metals close to the Mott transition

Nature volume 449, pages 584–587 (2007)Cite this article

Abstract

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.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Structure and phase diagram of κ-(BEDT-TTF) 2X.
Figure 2: The Nernst effect in κ-NCS.
Figure 3: The Nernst effect in κ-Br.

Similar content being viewed by others

References

  1. Tinkham, M. Introduction to Superconductivity 2nd edn (Dover Publications, Mineola, New York, 2004)

    Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  3. Ishiguro, T., Yamaji, K. & Saito, G. Organic Superconductors 2nd edn (Springer, Berlin, 2006)

    Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  Google Scholar 

  7. Mayaffre, H., Wzietek, P., Lenoir, C., Jerome, D. & Batail, P. C-13 study of a quasi-2-dimensional organic superconductor κ-(ET)2Cu[N(CN)2]Br. Europhys. Lett. 28, 205–210 (1994)

    Article  ADS  CAS  Google Scholar 

  8. Powell, B. J. & McKenzie, R. H. Strong electronic correlations in superconducting organic charge transfer salts. J. Phys. Condens. Matter 18, R827–R866 (2006)

    Article  ADS  CAS  Google Scholar 

  9. Caulfield, J. 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)

    Article  ADS  CAS  Google Scholar 

  10. Kagawa, F., Miyagawa, K. & Kanoda, K. Unconventional critical behaviour in a quasi-two-dimensional organic conductor. Nature 436, 534–537 (2005)

    Article  ADS  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  12. Xu, Z. A., Ong, N. P., Wang, Y., Kakeshita, T. & Uchida, S. Vortex-like excitations and the onset of superconducting phase fluctuation in underdoped La2-xSrxCuO4 . Nature 406, 486–488 (2000)

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  15. Wang, Y., Li, L. & Ong, N. P. Nernst effect in high-T c superconductors. Phys. Rev. B 73, 024510 (2006)

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  18. Logvenov, G. Y. 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)

    Article  ADS  CAS  Google Scholar 

  19. Analytis, J. G. 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)

    Article  ADS  Google Scholar 

  20. Sasaki, T. 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)

    Article  ADS  Google Scholar 

  21. Nam, M.-S. 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)

    Article  CAS  Google Scholar 

  22. Carrington, A. 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)

    Article  ADS  CAS  Google Scholar 

  23. Lee, P. A., Nagosa, N. & Wen, X.-G. Doping a Mott insulator: physics of high-temperature superconductivity. Rev. Mod. Phys. 78, 17–85 (2006)

    Article  ADS  CAS  Google Scholar 

  24. Emery, V. J. & Kivelson, S. A. Importance of phase fluctuations in superconductors with small superfluid density. Nature 374, 434–437 (1995)

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  27. Larkin, M. I., Kinkhabwala, A., Uemura, Y. J., Sushko, Y. & Saito, G. Pressure dependence of the magnetic penetration depth in κ-(BEDT-TTF)2Cu(NCS)2 . Phys. Rev. B 64, 144514 (2001)

    Article  ADS  Google Scholar 

  28. Pratt, F. L. & Blundell, S. J. Universal scaling relations in molecular superconductors. Phys. Rev. Lett. 94, 097006 (2005)

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  31. Powell, B. J. & McKenzie, R. H. Half-filled layered organic superconductors and the resonating-valence-bond theory of the Hubbard-Heisenberg model. Phys. Rev. Lett. 94, 047004 (2005)

    Article  ADS  CAS  Google Scholar 

  32. Gan, J. Y., Zhang, F. C. & Su, Z. B. Theory of gossamer and resonating valence bond superconductivity. Phys. Rev. B 71, 014508 (2005)

    Article  ADS  Google Scholar 

  33. Ussishkin, I., Sondhi, S. L. & Huse, D. A. Gaussian superconducting fluctuations, thermal transport, and the Nernst effect. Phys. Rev. Lett. 89, 287001 (2002)

    Article  ADS  Google Scholar 

Download references

Acknowledgements

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

Authors and Affiliations

  1. Department of Physics, Clarendon Laboratory, 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

Authors
  1. Moon-Sun Nam
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Arzhang Ardavan
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Stephen J. Blundell
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. John A. Schlueter
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Arzhang Ardavan.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Nam, MS., Ardavan, A., Blundell, S. et al. Fluctuating superconductivity in organic molecular metals close to the Mott transition. Nature 449, 584–587 (2007). https://doi.org/10.1038/nature06182

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature06182

This article is cited by

Comments

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.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing