title: Off-diagonal Bethe ansatz and exact solution of a topological spin ring.
abstract: 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 a Möbius-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 are discussed in detail. It is found that the excitation spectrum indeed shows a nontrivial topological nature.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Junpeng
authors.initials: J
authors.lastname: Cao
authors.forename: Wen-Li
authors.initials: WL
authors.lastname: Yang
authors.forename: Kangjie
authors.initials: K
authors.lastname: Shi
authors.forename: Yupeng
authors.initials: Y
authors.lastname: Wang