Exact surface energy and helical spinons in the XXZ spin chain with arbitrary nondiagonal boundary fields

Yi Qiao, Junpeng Cao, 2, 3, 4 Wen-Li Yang, 5, 6, 7, ∗ Kangjie Shi, and Yupeng Wang 4, 8, † Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, China Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China Peng Huanwu Center for Fundamental Theory, Xian 710127, China Institute of Modern Physics, Northwest University, Xian 710127, China School of Physics, Northwest University, Xian 710127, China Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xian 710127, China The Yangtze River Delta Physics Research Center, Liyang, Jiangsu 213300, China