Multi-photon excited states of two-dimensional strongly correlated electron systems

The effective Hamiltonian of the Hubbard model for the multi-photon excited states is derived by assuming strong Coulomb repulsion. By diagonalizing the effective Hamiltonian exactly, the lowest energy state in two-photon excited manifold is calculated in the two-dimensional Hubbard model at half-filling, and its physical properties are investigated. The antiferromagnetic spin order characteristic of the ground state is destroyed by two-photon excitation and three phases which have different electronic orders from that of the ground state are photo-generated. The analysis of several correlation functions suggests that they are of spiral spin state and two different d-wave superconducting states.