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_c2 ^S for the small gap band (of order H_c2/100). We present results on the skutterudite heavy-fermion compound PrOs₄Sb ₁₂ (T_c ≈ 1.8K), 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 CeCoIn₅ (T _c ≈ 2.3K). Although the proximity of this last system to a quantum critical point prevents quantitative analysis of the values of the gaps as in PrOs₄Sb₁₂, it shows even stronger multigap effects (H _c2^S ≈ H_c2/1000...), backing the ideas that the multiband behavior is intimately related to the role of the f electrons in the pairing mechanism.