Thermodynamic Properties of the One-Dimensional Kondo Insulators Studied by the Density Matrix Renormalization Group Method

Thermodynamic properties of the one-dimensional Kondo lattice model at half-filling are studied by the density matrix renormalization group method applied to the quantum transfer matrix. Spin susceptibility, charge susceptibility, and specific heat are calculated down to T = 0.1t for various exchange constants. The obtained results clearly indicate crossover behavior from the high-temperature regime of nearly independent localized spins and conduction electrons to the low-temperature regime where the two degrees of freedom couple strongly. The low-temperature energy scales of the charge and spin susceptibilities are determined and are equal to the quasiparticle gap and the spin gap, respectively, for weak exchange couplings.