The London penetration depth λ(T) was measured in single crystals of Ce1-xRxCoIn5, R = La, Nd, and Yb down to Tmin ≈ 50mK (Tc/Tmin ∼ 50) using a tunnel-diode resonator. In the cleanest samples Δλ(T) is best described by the power law Δλ(T) α Tn, 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 Tc; 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.
H. Kim et al., "Nodal to Nodeless Superconducting Energy-Gap Structure Change Concomitant with Fermi-Surface Reconstruction in the Heavy-Fermion Compound CeCoIn₅," Physical Review Letters, vol. 114, no. 2, article no. 27003, American Physical Society (APS), Jan 2015.
The definitive version is available at https://doi.org/10.1103/PhysRevLett.114.027003
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© 2015 American Physical Society (APS), All rights reserved.
15 Jan 2015