Takenaka T, Mizukami Y, Wilcox J A, Konczykowski M, Seiro S, Geibel C, Tokiwa Y, Kasahara Y, Putzke C, Matsuda Y, Carrington A, Shibauchi T
Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan.
H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, England.
Phys Rev Lett. 2017 Aug 18;119(7):077001. doi: 10.1103/PhysRevLett.119.077001.
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 CeCu_{2}Si_{2} 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 CeCu_{2}Si_{2}. 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.
反铁磁自旋涨落机制下非传统配对的一个关键方面是，超导能隙在费米面的不同部分必须具有相反的符号。鉴于重费米子超导体CeCu₂Si₂长期以来一直被视为库珀对由磁介导的超导体的典型例子，最近对其非节点能隙结构的观测结果就显得非常令人惊讶。在此，我们展示了一项关于电子辐照引入的可控点缺陷对CeCu₂Si₂中与温度相关的磁穿透深度λ(T)影响的研究。我们发现完全能隙态对无序具有鲁棒性，这表明对于符号变化的能隙结构所预期的低能束缚态并非由非磁性杂质诱导产生。这为无符号反转的s₊₊波超导性提供了体证据。
