Exact solutions and elementary excitations in the XXZ spin chain with   unparallel boundary fields
  By using a set of gauge transformations, the exact solutions of the XXZ spin chain with unparallel boundary magnetic fields are derived in the framework of the algebraic Bethe ansatz. In the easy-plane case, we show the elementary excitations are some kind of spinons without definite spin because the U(1) symmetry is broken, while in the easy-axis ferromagnetic case a spiral state is realized in the ground state. The correlation functions, the spin torque as well as the spin voltage for the later case are also derived. 
Junpeng Cao, Hai-Qing Lin, Kang-jie Shi, Yupeng Wang