Yamashita Takuya, Takenaka Takaaki, Tokiwa Yoshifumi, Wilcox Joseph A, Mizukami Yuta, Terazawa Daiki, Kasahara Yuichi, Kittaka Shunichiro, Sakakibara Toshiro, Konczykowski Marcin, Seiro Silvia, Jeevan Hirale S, Geibel Christoph, Putzke Carsten, Onishi Takafumi, Ikeda Hiroaki, Carrington Antony, Shibauchi Takasada, Matsuda Yuji
Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan.
Sci Adv. 2017 Jun 23;3(6):e1601667. doi: 10.1126/sciadv.1601667. eCollection 2017 Jun.
In exotic superconductors, including high- 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 CeCuSi, 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 CeCuSi, 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.
在包括高铜氧化物在内的奇异超导体中，介导电子库珀对的相互作用被广泛认为具有磁性起源而非传统的电子 - 声子起源。对这种奇异配对的兴趣始于1979年在CeCuSi中发现重费米子超导性，该材料表现出强烈的反铁磁涨落。由各向异性排斥相互作用导致的非常规配对的一个标志是，超导能隙随电子动量的变化而改变符号，这通常会导致能隙在某些点处变为零，即节点的出现。我们报告了对CeCuSi的低温比热、热导率和磁穿透深度的测量结果，证明在费米面的任何点都不存在能隙节点。此外，电子辐照实验表明，即使电子平均自由程变得比超导相干长度短得多，超导性依然存在。这表明超导性对杂质具有鲁棒性，意味着能隙函数没有符号变化。这些结果表明，与长期以来的观点相反，具有极强库仑排斥力的重电子可以凝聚成一个完全能隙的s波超导态，该态具有在位吸引配对相互作用。
