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arXiv · 2102.02643

Exact surface energy and helical spinons in the XXZ spin chain with arbitrary non-diagonal boundary fields

Yi Qiao·Junpeng Cao·Wen-Li Yang·Kangjie Shi·Yupeng Wang
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Abstract

An analytic method is proposed to compute the surface energy and elementary excitations of the XXZ spin chain with generic non-diagonal boundary fields. For the gapped case, in some boundary parameter regimes the contributions of the two boundary fields to the surface energy are non-additive. Such a correlation effect between the two boundaries also depends on the parity of the site number $N$ even in the thermodynamic limit $N\to\infty$. For the gapless case, contributions of the two boundary fields to the surface energy are additive due to the absence of long-range correlation in the bulk. Although the $U(1)$ symmetry of the system is broken, exact spinon-like excitations, which obviously do not carry spin-$\frac12$, are observed. The present method provides an universal procedure to deal with quantum integrable systems either with or without $U(1)$ symmetry.

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Yi Qiao, Junpeng Cao, Wen-Li Yang, Kangjie Shi, Yupeng Wang. 2021-01-31. Exact surface energy and helical spinons in the XXZ spin chain with arbitrary non-diagonal boundary fields. https://doi.org/10.1103/physrevb.103.l220401

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