η -pairing in correlated fermion models with spin-orbit coupling

The authors study the $\ensuremath{\eta}$-pairing phenomenon in correlated fermion models with spin-orbit coupling. Spin-orbit coupled systems are usually thought to possess no continuous symmetries, except the conventional U(1) particle-number symmetry. The $\ensuremath{\eta}$-pairing reveals an exact SU(2) pseudospin symmetry in a broad class of spin-orbit coupled Hubbard models. Furthermore, the authors construct an exactly solvable interacting Dirac-semimetal model that exhibits an exact pseudospin symmetry with fine-tuned parameters. This model hosts $\ensuremath{\eta}$-pairing and charge density wave ground states, which meet at an exactly solvable multicritical line.