Exact electron-pairing ground states of tight-binding models with local attractive interactions

We present a class of exactly solvable models of correlated electrons. The models are defined in any dimension d and consist of electron-hopping terms and local attractive interactions between electrons. For each even number of electrons less than or equal to 1/(d + 1)-filling, we find the exact ground state in which all electrons form pairs of a certain type, and thus the models exhibit an electron-pair condensation.