Electron pairing in the Hubbard model as a result of on-site repulsion fluctuations

We focus our quantitative analysis on the stability of insulator state in the Hubbard model at half-filling. Taking into account macroscopic fluctuation of the on-site repulsion, we consider the possibility of realizing a steady state which is characterized by electron pairing. Fluctuation of the on-site repulsion leads to the formation of holes in the form of excited states. The electron liquid has two possibilities of relaxation in the state with bare on-site repulsion U: trivial, to the initial state, and nontrivial to state in which electrons polarize holes forming electron-hole pairs. A steady state is determined by minimum energy for given U and its fluctuation δU . The values U and δU , for which the states with electron pairing are stable, are calculated. The proposed pairing mechanism is to some extent similar to the formation of a long-range pairing correlation in an optically induced Hubbard chain [].