Electrical permittivity driven metal-insulator transition in heterostructures of nonpolar Mott- and band insulators

摘要

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