A key aspect of unconventional pairing by the antiferromagnetic spin-fluctuation mechanism is that the superconducting energy gap must have 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 λ(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.
@article{arxiv.1705.06075,
title = {Full-gap superconductivity robust against disorder in heavy-fermion CeCu2Si2},
author = {T. Takenaka and Y. Mizukami and J. A. Wilcox and M. Konczykowski and S. Seiro and C. Geibel and Y. Tokiwa and Y. Kasahara and C. Putzke and Y. Matsuda and A. Carrington and T. Shibauchi},
journal= {arXiv preprint arXiv:1705.06075},
year = {2017}
}
Comments
5 pages, 4 figures + Supplemental Material (1 page, 1 figure). Will appear in Phys. Rev. Lett