We study the open XXZ spin chain in the anti-ferromagnetic regime and for generic longitudinal magnetic fields at the two boundaries. We discuss the ground state via the Bethe ansatz and we show that, for a chain of even length L and in a regime where both boundary magnetic fields are equal and bounded by a critical field, the spectrum is gapped and the ground state is doubly degenerate up to exponentially small corrections in L. We connect this degeneracy to the presence of a boundary root, namely an excitation localized at one of the two boundaries. We compute the local magnetization at the left edge of the chain and we show that, due to the existence of a boundary root, this depends also on the value of the field at the opposite edge, even in the half-infinite chain limit. Moreover we give an exact expression for the large time limit of the spin autocorrelation at the boundary, which we explicitly compute in terms of the form factor between the two quasi-degenerate ground states. This, as we show, turns out to be equal to the contribution of the boundary root to the local magnetization. We finally discuss the case of chains of odd length.
Cited by 4
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Phys. Rev. B 101, 085133 (2020) [Crossref]
Pei et al., On scalar products and form factors by separation of variables: the antiperiodic XXZ model
J. Phys. A: Math. Theor. 55, 015205 (2022) [Crossref]
Buča et al., Bethe ansatz approach for dissipation: exact solutions of quantum many-body dynamics under loss
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De Nardis et al., Delta-Bose gas on a half-line and the Kardar–Parisi–Zhang equation: boundary bound states and unbinding transitions
J. Stat. Mech. 2020, 043207 (2020) [Crossref]
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- 1 Laboratoire de Physique Théorique et Modèles Statistiques [LPTMS]
- 2 Universiteit Gent / Ghent University
- Agence Nationale de la Recherche [ANR]
- Centre National de la Recherche Scientifique / French National Centre for Scientific Research [CNRS]
- Fonds Wetenschappelijk Onderzoek (FWO) (through Organization: Fonds voor Wetenschappelijk Onderzoek - Vlaanderen / Research Foundation - Flanders [FWO])
- Simons Foundation