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

Takaaki Takenaka, Yuta Mizukami, Joe A Wilcox, Marcin Konczykowski, Silvia Seiro, Christoph Geibel, Yoshifumi Tokiwa, Yuichi Kasahara, Y Matsuda, Antony Carrington, Takasada Shibauchi

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

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 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.
Original languageEnglish
Article number077001
JournalPhysical Review Letters
Volume119
Issue number7
DOIs
Publication statusPublished - 18 Aug 2017

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