Ames Laboratory and Department of Physics & Astronomy, Iowa State University, Ames, Iowa 50011, USA.
Department of Physics, Brookhaven National Laboratory, Upton, New York 11973, USA.
Phys Rev Lett. 2015 Jan 16;114(2):027003. doi: 10.1103/PhysRevLett.114.027003. Epub 2015 Jan 15.
The London penetration depth λ(T) was measured in single crystals of Ce_{1-x}R_{x}CoIn_{5}, R=La, Nd, and Yb down to T_{min}≈50 mK (T_{c}/T_{min}∼50) using a tunnel-diode resonator. In the cleanest samples Δλ(T) is best described by the power law Δλ(T)∝T^{n}, with n∼1, consistent with the existence of line nodes in the superconducting gap. Substitutions of Ce with La, Nd, and Yb lead to similar monotonic suppressions of T_{c}; however, the effects on Δλ(T) differ. While La and Nd substitution leads to an increase in the exponent n and saturation at n∼2, as expected for a dirty nodal superconductor, Yb substitution leads to n>3, suggesting a change from nodal to nodeless superconductivity. This superconducting gap structure change happens in the same doping range where changes of the Fermi-surface topology were reported, implying that the nodal structure and Fermi-surface topology are closely linked.
使用隧道二极管谐振器，我们在 Ce_{1-x}R_{x}CoIn_{5}（R=La、Nd 和 Yb）的单晶中测量了伦敦穿透深度 λ(T)，最低温度 T_{min}≈50 mK（T_{c}/T_{min}∼50）。在最干净的样品中，Δλ(T)最好用幂律 Δλ(T)∝T^{n}来描述，其中 n∼1，与超导能隙中的线节点的存在一致。用 La、Nd 和 Yb 替代 Ce 会导致 T_{c}的单调抑制；然而，对 Δλ(T)的影响不同。虽然 La 和 Nd 取代导致指数 n 的增加和 n∼2 的饱和，这与脏节点超导体的预期一致，但 Yb 取代导致 n>3，表明从节点到无节点超导性的转变。这种超导能隙结构的变化发生在报道费米表面拓扑结构变化的相同掺杂范围内，这意味着节点结构和费米表面拓扑结构密切相关。
