Theoretical studies on many-band effects in superconductivity and magnetism


  • Dedicated to Professor Kizashi Yamaguchi for his 60th birthday.


We present a two-dimensional two-sublattice system to investigate two-band effects in magnetism and superconductivity. The spin susceptibility of the sublattice system is calculated, and the expression of the effective exchange integral in Heisenberg model for the sublattice is derived in the framework of the Hubbard model. We find the possibility of the appearance of ferromagnetic order around half-filling in a two-band system. Within the extended Hubbard model, a coupled gap equation for the two-band superconductivity is also derived by using a mean-field approximation. The results suggest that the superconducting order becomes larger by the pair-scattering process. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004