Superconductivity from a non-Fermi-liquid metal: Kondo fluctuation mechanism in slave-fermion theory

Abstract

We find new mechanism of superconductivity beyond the spin-fluctuation theory, the standard model for unconventional superconductivity in the weak coupling approach, where Kondo fluctuations result in multi-gap superconductivity around an antiferromagnetic quantum critical point of the slave-fermion theory. Fingerprints of the hybridization mechanism are two kinds of resonance modes in not only spin but also charge fluctuations, originating from $d-wave$ pairing of conduction electrons and spinless holons, respectively, thus differentiated from the spin-fluctuation mechanism. We show that the ratio between each superconducting gap for conduction electrons $\Delta_{c}$ and holons $\Delta_{f}$ and the transition temperature $T_{c}$ is $2\Delta_{c} / T_{c} \sim 9$ and $2\Delta_{f} / T_{c} \sim \mathcal{O}(10^{-1})$, remarkably consistent with $CeCoIn_{5}$.