Kozo Okada

Fermi Liquid Theory on the Basis of Periodic Anderson Hamiltonian with Orbital Degeneracy

--~ The Fermi liquid theory on the basis of the periodic Anderson Hamiltonian is extended to the case with orbital degeneracy. The general expressions for T-linear term of specific heat, spin and orbital susceptibilities and T2-term of resistivity are derived. These results confirm that the general relations derived for the single orbital case hold also in the degenerate case, though they are given in matrix forms. For example, the T2-term of resistivity is proportional to the square of the mass enhancement factor, when the Coulomb repulsion is large enough to suppress the charge fluctuation of f-electrons. Moreover, it is shown that f-orbital degeneracy suppresses the magnetic instability and the Fermi liquid theory can be applied to a larger value of U compared with the single orbital case.

STABILITY OF A VORTEX NEAR THE SURFACE OF FERROMAGNETIC SUPERCONDUCTORS.

Near the surface of ferromagnetic superconductors, the free energy difference between the single vortex state and the no vortex state is calculated as a function of the distance between the vortex and the surface for various values of temperature T and external magnetic field H 0 . It is shown that the vortex is bound near the surface at T < T 0 under H 0 higher than a critical value, where T 0 is the characteristic temperature below which the external magnetic field penetrates into the crystal in an oscillatory fashion. The interaction between the vortex and the penetrating magnetic field plays an important role in the stability of the vortex near the surface. A possibility of the self-induced vortex state near the surface is predicted.

Mixed states of films of ferromagnetic superconductors

The magnetization process in films of ferromagnetic superconductors is studied theoretically by concentrating mainly on the region near the lower critical field H c1 . Below a characteristic temperature, where the magnetic interaction energy plays an important role, the following are predicted: the unusual dependence of H c1 on the film thickness, the discontinuity of the magnetization curve due to the change of the vortex lattice structure and the change of the transition type from II/1 to II/2 with decreasing the film thickness. The possibility of another type (II/3) of phase transition is also discussed. The mechanisms of these results are analyzed with particular attention to the roles of the interaction between each vortex and the magnetic field penetrating from the surface, the surface-affected intervortex interaction and the saturation effect of the magnetization which is mainly caused by the penetrating field.