Professor Chigak Itoi
Nihon University, Japan

Title: Exact ground states with interface in a deformed flat-band Hubbard model

Abstract: I find a set of exact ground states in a deformed flat-band Hubbard model. This model is obtained from the flat-band Hubbard model by reducing the original SU(2) symmetry to U(1) symmetry. This model has two ferromagnetic ground states which are translationally invariant. On the other hand, other ground states have an interface which breaks the translational symmetry. The magnon excitation above the translationally invariant ground states has an energy gap, while the excitation above the interface ground states becomes gapless.