Superconducting condensation energy in a diluted Kondo lattice

Heavy fermion compounds are host to many interesting but poorly understood strong correlation effects, leading in exceptional cases to unconventional superconductivity. CeCoIn5 is such an example of an ambient pressure heavy fermion superconductor with a Tc of 2.3K. Such compounds are best described as a Kondo lattice, where Ce, Yb or U ions form a periodic lattice of magnetic moments coupled to the conduction electrons via antiferromagnetic exchange interaction. Dilution, or substitution, of the Kondo ion with a lanthanide, actinide or alkali-earth element that does not participate in the Kondo lattice, results in the so-called Kondo hole. The electron scattering off the Kondo hole leads to significant changes in both the normal and superconducting properties. We have investigated the suppression of superconductivity in CeCoIn5 diluted with La, Yb, Y, Ca, Th, Gd, Er, Eu and Lu via specific heat measurements on well characterized single crystals. The suppression of the superconducting condensation energy exhibits a remarkable departure from the Abrikosov-Gorkov impurity pair breaking picture, emphasizing that the Kondo holes are no ordinary pair-breakers.