2025/11/18 by Wildeboer, Julia, Lajer, Marton, Konik, Robert M.
Computer Science · Physics and Astronomy · #Anisotropy #Antiferromagnetism #FOS: Physical sciences #Meson #Physics of Superconductivity and Magnetism #Quantum #Quantum Information and Cryptography #Quantum chaos #Quantum entanglement #Quantum many-body systems #Spectral line #Spin (aerodynamics) #Spinon #Strongly Correlated Electrons (cond-mat.str-el)
paper · open access · doi:10.48550/arxiv.2511.14847
published in arXiv (Cornell University) (Cornell University)
openalex publication_date 2025/11/18 · openalex created_date 2025/11/23 · openalex updated_date 2026/07/28
Confinement of fractionalized excitations can strongly restructure many-body spectra. We investigate this phenomenon in the gapped spin-(1)/(2) XXZ chain subject to a staggered field, where spinons bind into domain-wall ``mesons'' deep in the antiferromagnetic phase. We present evidence that this non-integrable model exhibits both Hilbert space fractionalization and quantum scar formation as controlled by the anisotropy parameter Δ. Exact diagonalization across symmetry-resolved sectors reveals a crossover from Gaussian-orthogonal (chaotic) level statistics at weak anisotropy Δ∼ 1 to non-ergodic behavior deep in the antiferromagnetic regime Δ≫ 1 through scrutinizing the adjacent gap ratios, accompanied by a striking banding of eigenstates by domain-wall number in correlation and entanglement measures. The Page-like entanglement dome characteristic of chaotic spectra gives way to suppressed, band-resolved entanglement consistent with emergent quasi-conservation of domain walls. To investigate further the formation mechanism of mesonic scar states, we carry out meson spectroscopy near the two-spinon threshold and compare with the analytic ladder predicted by Rutkevich [Phys. Rev. B 106, 134405 (2022)]. We test the theory through continuum-relative bindings, an offset-removed Airy scaling collapse, and explicit two-meson thresholds that determine the number of stable meson levels. The low-lying spectrum shows close quantitative agreement, while deviations at higher energies are consistent with finite-size and subleading corrections. These results establish a unified account of confinement-induced nonergodicity and provide a template for quantitative meson spectroscopy in quantum spin chains.