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Magnetically driven superconductivity in CeCu2Si2

Nature Physics volume 7, pages 119–124 (2011)Cite this article

Abstract

The origin of unconventional superconductivity, including high-temperature and heavy-fermion superconductivity, is still a matter of controversy. Spin excitations instead of phonons are thought to be responsible for the formation of Cooper pairs. Using inelastic neutron scattering, we present the first in-depth study of the magnetic excitation spectrum in momentum and energy space in the superconducting and the normal states of CeCu2Si2. A clear spin excitation gap is observed in the superconducting state. We determine a lowering of the magnetic exchange energy in the superconducting state, in an amount considerably larger than the superconducting condensation energy. Our findings identify the antiferromagnetic excitations as the main driving force for superconducting pairing in this prototypical heavy-fermion compound located near an antiferromagnetic quantum critical point.

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Figure 1: Schematic phase diagram around the QCP, crystal structure and nearly isotropic spin fluctuations of CeCu2Si2.
Figure 2: Inelastic neutron scattering spectra in the normal and superconducting states of CeCu2Si2.
Figure 3: Magnetic response, relaxation rate and spin gap at the AF wave vector of CeCu2Si2.
Figure 4: Dispersion of the magnetic response in superconducting CeCu2Si2.
Figure 5: Schematic plot of the imaginary part of the dynamic spin susceptibility Imχ(QAF,ω) in the normal and superconducting states.

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Acknowledgements

We greatly acknowledge helpful discussions with A. Chubukov, P. Coleman, T. Dahm, I. Eremin, B. Fåk, A. Hiess, D. Scalapino and P. Thalmeier. This work was supported by the Deutsche Forschungsgemeinschaft through Forschergruppe 960 ‘Quantum phase transitions’, as well as by the NSF Grant No. DMR-1006985 and the Robert A. Welch Foundation Grant No. C-1411.

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Authors and Affiliations

  1. Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany

    O. Stockert, J. Arndt, C. Geibel, H. S. Jeevan, S. Kirchner & F. Steglich

  2. Institut für Festkörperphysik, Technische Universität Dresden, 01062 Dresden, Germany

    E. Faulhaber & M. Loewenhaupt

  3. Gemeinsame Forschergruppe Helmholtz-Zentrum Berlin — TU Dresden, 85747 Garching, Germany

    E. Faulhaber

  4. I. Physikalisches Institut, Universität Göttingen, 37077 Göttingen, Germany

    H. S. Jeevan

  5. Max-Planck-Institut für Physik komplexer Systeme, 01187 Dresden, Germany

    S. Kirchner

  6. Jülich Centre for Neutron Science, Forschungszentrum Jülich, Outstation at Institut Laue–Langevin, 38042 Grenoble, France

    K. Schmalzl & W. Schmidt

  7. Department of Physics and Astronomy, Rice University, Houston, Texas, 77005, USA

    Q. Si

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  1. O. Stockert
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Contributions

H.S.J. and C.G. synthesised the sample. O.S., J.A., E.F., M.L., K.S. and W.S. carried out the measurements. O.S., J.A. and S.K. analysed the data. S.K. and Q.S. carried out theoretical calculations. O.S., S.K., Q.S. and F.S. wrote the manuscript. O.S., S.K., Q.S. and F.S. planned and managed the project.

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Correspondence to O. Stockert.

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The authors declare no competing financial interests.

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Stockert, O., Arndt, J., Faulhaber, E. et al. Magnetically driven superconductivity in CeCu2Si2. Nature Phys 7, 119–124 (2011). https://doi.org/10.1038/nphys1852

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