The substitution of ytterbium for cerium in the unconventional superconductor cerium–cobalt–indium (CeCoIn5) reveals a completely unexpected example of a nodeless energy gap—an energy range forbidden to electrons. CeCoIn5 is believed to have an energy-momentum structure with d-wave gap symmetry. This d-wave gap symmetry is shaped like a four-petal flower with special points where the energy gap becomes zero, called nodes. The team discovered that ytterbium substitution resulted in an anomalous transformation of the nodal d-wave gap into a nodeless structure. Interestingly, substitution with lanthanum and neodymium did not. Furthermore, it seems that this transformation is associated with changes observed in the electronic structure, providing insight into its connection to superconductivity. Identifying the superconducting gap symmetry, one of the central properties of superconductors, provides vital new information into the fundamental mechanisms responsible for this phenomenon.
Nodal to Nodeless Superconducting Energy Gap Structure Change Concomitant with Fermi Surface Reconstruction in the Heavy-Fermion CeCoIn5