Electron-hole liquids in transition-metal oxide heterostructures

Appropriately designed transition-metal-oxide heterostructures involving small band-gap Mott insulators are argued to support spatially separated electron and hole gasses at equilibrium. Spatial separations and carrier densities favoring the formation of excitonic states are achievable. The excitonic states may exhibit potentially novel properties. Energetic estimates are given, candidate material systems are discussed, and the possibility of large photovoltaic effects is mentioned.