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

Abstract

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 $J\ensuremath{\rightarrow}0$ for any ${U}_{c}$ with an exponential form, ${\ensuremath{\Delta}}_{s}\ensuremath{\propto}\mathrm{exp}[\ensuremath{-}\frac{1}{\ensuremath{\alpha}({U}_{c})J\ensuremath{\rho}}]$. The exponent, $\ensuremath{\alpha}({U}_{c})$, is determined as a function of ${U}_{c}$. The charge gap is generally much larger than the spin gap. In the limit of $J\ensuremath{\rightarrow}0$, the charge gap vanishes as ${\ensuremath{\Delta}}_{c}=\frac{1}{2}J$ 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.