Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu2Si2

Takuya Yamashita, Takaaki Takenaka, Yoshifumi Tokiwa, Joe Wilcox, Yuta Mizukami, Daiki Terazawa, Yuichi Kasahara, Shunichiro Kittaka, Toshiro Sakakibara, Marcin Konczykowski, Silvia Seiro, Hirale Jeevan, Chrisoph Geibel, Carsten Putzke, Takafumi Onishi, Hiroaki Ikeda, Antony Carrington, Takasada Shibauchi, Yuji Matsuda

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

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Abstract

In exotic superconductors, including high-Tc copper oxides, the interactions mediating electron Cooper pairing are widely considered to have a magnetic rather than a conventional electron-phonon origin. Interest in this exotic pairing was initiated by the 1979 discovery of heavy-fermion superconductivity in CeCu2Si2, which exhibits strong antiferromagnetic fluctuations. A hallmark of unconventional pairing by anisotropic repulsive interactions is that the superconducting energy gap changes sign as a function of the electron momentum, often leading to nodes where the gap goes to zero. We report low-temperature specific heat, thermal conductivity, and magnetic penetration depth measurements in CeCu2Si2, demonstrating the absence of gap nodes at any point on the Fermi surface. Moreover, electron irradiation experiments reveal that the superconductivity survives even when the electron mean free path becomes substantially shorter than the superconducting coherence length. This
indicates that superconductivity is robust against impurities, implying that there is no sign change in the gap function. These results show that, contrary to long-standing belief, heavy electrons with extremely strong Coulomb repulsions can condense into a fully gapped s-wave superconducting state, which has an on-site attractive pairing interaction.
Original languageEnglish
Article numbere1601667
Number of pages7
JournalScience Advances
Volume3
Issue number6
DOIs
Publication statusPublished - 23 Jun 2017

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