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Journal Article

Full-Gap Superconductivity Robust against Disorder in Heavy-Fermion CeCu2Si2


Geibel,  C.
Christoph Geibel, Physics of Quantum Materials, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Takenaka, T., Mizukami, Y., Wilcox, J. A., Konczykowski, M., Seiro, S., Geibel, C., et al. (2017). Full-Gap Superconductivity Robust against Disorder in Heavy-Fermion CeCu2Si2. Physical Review Letters, 119(7): 077001, pp. 1-5. doi:10.1103/PhysRevLett.119.077001.

Cite as: https://hdl.handle.net/11858/00-001M-0000-002D-DE45-4
A key aspect of unconventional pairing by the antiferromagnetic spin-fluctuation mechanism is that the superconducting energy gap must have the opposite sign on different parts of the Fermi surface. Recent observations of non-nodal gap structure in the heavy-fermion superconductor CeCu2Si2 were then very surprising, given that this material has long been considered a prototypical example of a superconductor where the Cooper pairing is magnetically mediated. Here we present a study of the effect of controlled point defects, introduced by electron irradiation, on the temperature-dependent magnetic penetration depth. lambda (T) in CeCu2Si2. We find that the fully gapped state is robust against disorder, demonstrating that low-energy bound states, expected for sign-changing gap structures, are not induced by nonmagnetic impurities. This provides bulk evidence for s(||)-wave superconductivity without sign reversal.