Skip to main content

Thank you for visiting 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.

A distinct bosonic mode in an electron-doped high-transition-temperature superconductor


Despite recent advances in understanding high-transition-temperature (high-Tc) superconductors, there is no consensus on the origin of the superconducting ‘glue’: that is, the mediator that binds electrons into superconducting pairs. The main contenders are lattice vibrations1,2 (phonons) and spin-excitations3,4, with the additional possibility of pairing without mediators5. In conventional superconductors, phonon-mediated pairing was unequivocally established by data from tunnelling experiments6. Proponents of phonons as the high-Tc glue were therefore encouraged by the recent scanning tunnelling microscopy experiments on hole-doped Bi2Sr2CaCu2O8-δ (BSCCO) that reveal an oxygen lattice vibrational mode whose energy is anticorrelated with the superconducting gap energy scale7. Here we report high-resolution scanning tunnelling microscopy measurements of the electron-doped high-Tc superconductor Pr0.88LaCe0.12CuO4 (PLCCO) (Tc = 24 K) that reveal a bosonic excitation (mode) at energies of 10.5 ± 2.5 meV. This energy is consistent with both spin-excitations in PLCCO measured by inelastic neutron scattering (resonance mode)8 and a low-energy acoustic phonon mode9, but differs substantially from the oxygen vibrational mode identified in BSCCO. Our analysis of the variation of the local mode energy and intensity with the local gap energy scale indicates an electronic origin of the mode consistent with spin-excitations rather than phonons.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Prominent low energy spectral features on PLCCO at a temperature of 5.5 K.
Figure 2: Gap distribution, statistics and temperature dependence.
Figure 3: Statistics of the mode observed as peaks in d2I /d V2.
Figure 4: Variation of local mode energy and intensity with the local gap energy scale.


  1. 1

    McQueeney, R. J. et al. Anomalous dispersion of LO phonons in La1. 85Sr0. 15CuO4 at low temperatures. Phys. Rev. Lett. 82, 628–631 (1999)

    CAS  Article  ADS  Google Scholar 

  2. 2

    Lanzara, A. et al. Evidence for ubiquitous strong electron–phonon coupling in high-temperature superconductors. Nature 412, 510–514 (2001)

    CAS  Article  ADS  Google Scholar 

  3. 3

    Rossat-Mignod, J. et al. Neutron scattering study of the YBa2Cu3O6+x system. Physica C 185–189, 86–92 (1991)

    Article  ADS  Google Scholar 

  4. 4

    Norman, M. R. et al. Unusual dispersion and line shape of the superconducting state spectra of Bi2Sr2CaCu2O8+δ . Phys. Rev. Lett. 79, 3506–3509 (1997)

    CAS  Article  ADS  Google Scholar 

  5. 5

    Anderson, P. W. Is there glue in cuprate superconductors? Science 316, 1705–1707 (2007)

    CAS  Article  Google Scholar 

  6. 6

    McMillan, W. L. & Rowell, J. M. Lead phonon spectrum calculated from superconducting density of states. Phys. Rev. Lett. 14, 108–112 (1965)

    CAS  Article  ADS  Google Scholar 

  7. 7

    Lee, J. et al. Interplay of electron-lattice interactions and superconductivity in Bi2Sr2CaCu2O8+δ . Nature 442, 546–550 (2006)

    CAS  Article  ADS  Google Scholar 

  8. 8

    Wilson, S. D. et al. Resonance in the electron-doped high-transition-temperature superconductor Pr0. 88LaCe0. 12CuO4–δ . Nature 442, 59–62 (2006)

    CAS  Article  ADS  Google Scholar 

  9. 9

    d’Astuto, M. et al. Anomalous dispersion of longitudinal optical phonons in Nd1. 86Ce0. 14CuO4+δ determined by inelastic X-ray scattering. Phys. Rev. Lett. 88, 167002 (2002)

    Article  ADS  Google Scholar 

  10. 10

    Pan, Z.-H. et al. Universal quasiparticle decoherence in hole- and electron-doped high-T c cuprates. Preprint at 〈〉 (2006)

  11. 11

    Kashiwaya, S. et al. Tunneling spectroscopy of superconducting Nd1. 85Ce0. 15CuO4–δ . Phys. Rev. B 57, 8680–8686 (1998)

    CAS  Article  ADS  Google Scholar 

  12. 12

    Littlewood, P. B. & Varma, C. M. Anisotropic tunneling and resistivity in high-temperature superconductors. Phys. Rev. B 45, 12636 (1992)

    CAS  Article  ADS  Google Scholar 

  13. 13

    Kirtley, J. R. & Scalapino, D. J. Inelastic-tunneling model for the linear conductance background in the high-T c superconductors. Phys. Rev. Lett. 65, 798–800 (1990)

    CAS  Article  ADS  Google Scholar 

  14. 14

    Matsui, H. et al. Direct observation of a nonmonotonic d x 2 − y 2 -wave superconducting gap in the electron-doped high-Tc superconductor Pr0. 89LaCe0. 11CuO4 . Phys. Rev. Lett. 95, 017003 (2005)

    CAS  Article  Google Scholar 

  15. 15

    Shan, L. et al. An universal law of the superconducting gap in the electron-doped cuprate superconductors. Phys. Rev. B (in the press). Preprint at 〈〉 (2007)

  16. 16

    Pilgram, S., Rice, T. M. & Sigrist, M. Role of inelastic tunneling through the insulating barrier in scanning-tunneling-microscope experiments on cuprate superconductors. Phys. Rev. Lett. 97, 117003 (2006)

    CAS  Article  ADS  Google Scholar 

  17. 17

    Zhao, J. et al. Neutron-spin resonance in optimally electron-doped superconductor Nd1. 85Ce0. 15CuO4 . Phys. Rev. Lett. 99, 017001 (2007)

    Article  ADS  Google Scholar 

  18. 18

    Zhu, J. X. et al. Fourier-transformed local density of states and tunneling into a d-wave superconductor with bosonic modes. Phys. Rev. B 73, 014511 (2006)

    Article  ADS  Google Scholar 

  19. 19

    Lavrov, A. N. et al. Spin-flop transition and the anisotropic magnetoresistance of Pr1. 3-xLa0. 7CexCuO4: Unexpectedly strong spin-charge coupling in the electron doped cuprates. Phys. Rev. Lett. 92, 227003 (2004)

    CAS  Article  ADS  Google Scholar 

  20. 20

    Pintschovius, L. et al. Inelastic neutron scattering study of La2CuO4 . Prog. High Temp. Supercond. 21, 36–45 (1989)

    Google Scholar 

  21. 21

    Renker, B. et al. Electron–phonon coupling in HTC superconductors evidenced by inelastic neutron scattering. Physica B 180, 450–452 (1992)

    Article  ADS  Google Scholar 

  22. 22

    Pintschovius, L. & Reichardt, W. in Physical Properties of High Temperature Superconductors Vol. IV (ed. Ginsberg, D. M.) 295 (World Scientific, London, 1994)

    Google Scholar 

  23. 23

    Crawford, M. K. et al. Infrared active phonons in (Pr2–x Ce x )CuO4 . Solid State Commun. 73, 507–509 (1990)

    CAS  Article  ADS  Google Scholar 

  24. 24

    Homes, C. C. et al. Optical properties of Nd1. 85Ce0. 15CuO4 . Phys. Rev. B 56, 5525–5534 (1997)

    CAS  Article  ADS  Google Scholar 

  25. 25

    Lynn, J. W. et al. Phonon density of states and superconductivity in Nd1. 85Ce0. 15CuO4 . Phys. Rev. Lett. 66, 919–922 (1991)

    CAS  Article  ADS  Google Scholar 

  26. 26

    Persson, B. N. J. & Baratoff, A. Inelastic electron tunneling from a metal tip: the contribution from resonant processes. Phys. Rev. Lett. 59, 339–342 (1987)

    CAS  Article  ADS  Google Scholar 

  27. 27

    Hwang, J., Timusk, T. & Carbotte, J. P. Scanning-tunneling spectra of cuprates. Nature 446, E3–E4 (2007)

    CAS  Article  ADS  Google Scholar 

  28. 28

    Scalapino, D. J. Superconductivity: Pairing glue or inelastic tunnelling? Nature Phys. 2, 593–594 (2006)

    CAS  Article  ADS  Google Scholar 

  29. 29

    Eliashberg, G. M. Interactions between electrons and lattice vibrations in a superconductor. Sov. Phys. JETP 11, 696–702 (1960)

    MathSciNet  MATH  Google Scholar 

Download references


We thank A. V. Balatsky, E. W. Hudson, P. Richard, G. Murthy, J. Engelbrecht and J. C. Davis for discussions and comments. This work was supported by the NSF and the DOE.

Author information



Corresponding author

Correspondence to V. Madhavan.

Supplementary information

Supplementary Information

This file contains Supplementary Figures 1-5 with Legends and a brief summary of experimental parameters and methods. (PDF 3524 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Niestemski, F., Kunwar, S., Zhou, S. et al. A distinct bosonic mode in an electron-doped high-transition-temperature superconductor. Nature 450, 1058–1061 (2007).

Download citation

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.


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