Off-diagonal Bethe ansatz and exact solution of a topological spin ring

Understand

A general method is proposed for constructing the Bethe ansatz equations of integrable models without U(1) symmetry.

• As an example, the exact spectrum of the XXZ spin ring with M{\" o}bius like topological boundary condition is derived by constructing a modified T-Q relation based on the functional connection between the eigenvalues of the transfer matrix and the quantum determinant of the monodromy matrix.
• With the exact solution, the elementary excitations of the topological XX spin ring is discussed in detail.
• It is found that the excitation spectrum indeed shows a nontrivial topological nature.