Pressure-induced insulator-metal transitions in the spinless Falicov-Kimball model

The possibilities for pressure-driven insulator-metal transitions in the spinless Falicov-Kimball model are studied using small-cluster exact-diagonalization calculations. It is shown that for small values of the interaction strength U the Falicov-Kimball model undergoes an insulator-metal transition, which is accompanied by a discontinuous change of the energy gap. Thus, in the pressure-induced case, the model is capable of describing the insulator-metal transitions observed in some rare-earth compounds, e.g., in ${\mathrm{SmB}}_6$. In the general case, the valence transitions for small U have a staircase structure formed by the most homogeneous configurations with the smallest periods; however, the transitions between two such configurations (unlike the case of large U, where they are very sharp) are now gradual.