  Metallic interfaces between insulating perovskites are often observed in
heterostructures combining polar and nonpolar materials. In these systems, the
polar discontinuity across the interface may drive an electronic reconstruction
inducing free carriers at the interface. Here, we theoretically show that a
metallic interface between a Mott- and a band-insulator can also form in the
absence of a polar discontinuity. The condition for the appearance of such a
metallic state is consistent with the classical Mott criterion: the metallic
state is stable if the screening length falls below the effective Bohr radius
of a particle-hole pair. In this case, the metallic state bears a remarkable
similarity to the one found in polar/nonpolar heterostructures. On the other
hand, if the screening length approaches the size of the effective Bohr radius,
particles and holes are bound to each other resulting in an overall insulating
phase. We analyze this metal-insulator transition, which is tunable by the
dielectric constant, in the framework of the slave-boson mean-field theory for
a lattice model with both onsite and long-range Coulomb interactions. We
discuss ground-state properties and transport coefficients, which we derive in
the relaxation-time approximation. Interestingly, we find that the
metal-insulator transition is accompanied by a strong enhancement of the
Seebeck coefficient in the band-insulator region in the vicinity of the
interface. The implications of our theoretical findings for various
experimental systems such as nonpolar (110) interfaces are also discussed.
