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 U-c. It is shown that both the spin and charge gaps increase with increasing J and U-c. The spin gap vanishes in the limit of J-->0 for any U-c with an exponential form, Delta(s) proportional to exp[1/alpha(U-c)J rho]. The exponent, alpha(U-c), is determined as a function of U-c. The charge gap is generally much larger than the spin gap. In the limit of J-->0 the charge gap vanishes as Delta(c)=1/2J for U-c=0 but for a finite U-c it tends to a finite value, which is the charge gap of the Hubbard model.