EXACT SOLUTION OF THE ONE-DIMENSIONAL HUBBARD-MODEL IN A MAGNETIC-FIELD

By means of the Bethe-ansatz method, the one-dimensional Hubbard model with repulsive on-site coupling in an external magnetic field is solved exactly. It is found that the energy of the ground state depends on the magnetic flux phi through the ring formed by a periodic lattice chain, and the lowest-energy state corresponds to phi = n (hc/2e), with n an integer and -e the electron charge. The calculations illustrate that the strongly correlated Hubbard ring with periodic boundary conditions in its ground state is a superconducting ring. It can also be shown that the system possesses an internal SU(2) X SU(2) symmetry.