Spin and charge gaps in the one-dimensional Kondo-lattice model with Coulomb interaction between conduction electrons

The density-matrix renormalization-group method is applied to the one-dimensional Kondo-lattice model with the Coulomb interaction between the conduction electrons. The spin and charge gaps are calculated as a function of the exchange constant J and the Coulomb interaction Uc. It is shown that both the spin and charge gaps increase with increasing J and Uc. The spin gap vanishes in the limit of J→0 for any Uc with an exponential form, Δₛ∝exp[-1α(Uc)Jρ]. The exponent, α(Uc), is determined as a function of Uc. The charge gap is generally much larger than the spin gap. In the limit of J→0, the charge gap vanishes as Δc=1/2J for Uc=0 but for a finite Uc it tends to a finite value, which is the charge gap of the Hubbard model.