Multigap Superconductivity in Heavy Fermion Systems

Heavy fermion superconductors are largely studied for the rich variety of their unconventional ground states. But the discovery of new Pr and Ce based systems which are superconducting at zero pressure, revealed multigap effects with a remarkably low “critical" field scale H c 2 S for the small gap band (of order H c 2 /100). We present results on the skutterudite heavy-fermion compound PrOs 4 Sb 12 ( T c ≈1.8 K), where both the low field and the low temperature behavior of its thermal conductivity yield evidence for multigap superconductivity as well as new ongoing results on CeCoIn 5 ( T c ≈2.3 K). Although the proximity of this last system to a quantum critical point prevents quantitative analysis of the values of the gaps as in PrOs 4 Sb 12 , it shows even stronger multigap effects ( H c 2 S ≈ H c 2 /1000...), backing the ideas that the multiband behavior is intimately related to the role of the f electrons in the pairing mechanism.