Two-electron correlated motion due to Coulomb repulsion

A Hubbard-type model is derived from the microscopic Schr"odinger equation. We found that additional terms describing direct two-electron transitions must be added to the standard Hubbard Hamiltonian. Such a Hamiltonian generates two-electron pairing due to on-site Coulomb repulsion. We demonstrate that the electron pairs with opposite spin propagate across periodic structures via direct and sequential two-electron tunneling. This mechanism can be used for a generation of entangled electron current. Numerical calculations show stability of the electron pairs.