Unconventional full-gap superconductivity in Kondo lattice with semi-metallic conduction bands*

Non-local and anisotropic Cooper pairings are favored in heavy-electron materials with nearly localized f-electrons. On the other hand, the full-gap nature of the superconducting states in CeCu2Si2 and UBe13 have been revealed by the specific heat measurements in a rotating magnetic-field. Therefore, it is desirable to propose a new mechanism of superconductivity that is specific to heavy-electron materials.
Here we theoretically study the Kondo lattice with semi-metallic conduction bands, and propose the mechanism for full-gap superconductivity in f-electron systems. Based on the mean-field approach, we reveal that the superposition between electron conduction band and hole conduction band is realized through the formation of the Kondo-singlet states. The resultant ground state spontaneously breaks the gauge symmetry to make the system superconducting. This superconducting state is characterized by the composite pairing amplitude, which has been proposed in the context of two-channel Kondo lattice. We have demonstrated here that the semi-metallic conduction bands with electron and hole Fermi surfaces are closely related to the composite pairing.