Upper critical field in the superconducting Kondo lattice

The upper critical field Hc2 in the Kondo lattice was theoretically studied in connection with superconductivity in CeCu2Si2 and UBe13. To describe the coherent state in the Kondo lattice, a periodic Anderson model with multiple conduction bands was used. With the use of a single-site approximation for the self-energy of the f electron, a Fermi-liquid state was derived in the presence of external magnetic field. By assuming a singlet superconductivity of the Fermi liquid, Hc2 was calculated as a function of temperature and the scattering potentials due to impurities. In comparison with the experiments in CeCu2Si2 and UBe13, the nature of superconductivity in these compounds that is, singlet or triplet superconductivity was discussed.