-type thermoelectrics in oxide superlattices exploiting interface polarity*

Transition metal oxides and in particular their heterostructures are attractive for thermoelectric applications. We explore the implications of interface polarity in LaNiO₃/SrTiO₃(001) superlattices on structural, electronic, and thermoelectric properties by combining DFT+U calculations and Boltzmann transport theory. While superlattices containing (LaO)⁺/(TiO₂)⁰ interfaces result in an n-type material, a (NiO₂)^-/(SrO)⁰ stacking leads to p-type doping. We find that significant octahedral tilts are induced in the SrTiO₃ region and that the La-Sr distances act as a fingerprint of the interface type. In contrast to LaAlO₃/SrTiO₃(001), the electrostatic doping is accommodated in the metallic nickelate layers. The electronic structure displays an orbital-selective quantization of Ni-3d-derived quantum well states. Complex cylindrical Fermi surfaces emerge, which show a tendency towards nesting that depends on the interface polarity. Finally, we demonstrate that the thermoelectric response of the superlattice can be selectively controlled by a targeted interface design. This opens a route for constructing oxide-based thermoelectric generators [1].

[1] B. Geisler et al., PRB 95, 125301 (2017); patent pending