Metastable electron-pair states in a two-dimensional crystal

We study possible quantum states of two correlated electrons in a two-dimensional crystal and find a metastable energy band of the electron pair between the two lowest single-electron bands. These metastable states result from the interplay of electron correlations and the strength of the crystal potential. The two paired electrons are bound in the same unit cell in relative coordinates with an average distance between them about one third of the crystal period. Furthermore, we show how such electron-pairs can be stabilized in a many-electron system.