{
  "abstract": "The alternating spin-$(1,\\tfrac12)$ Heisenberg chain with a frustrating next-nearest-neighbor coupling $J_2$ loses its Lieb--Mattis moment through a discontinuous transition to a singlet whose nature was left open. Using an SU(2)-symmetric density-matrix renormalization group, in which the total spin is a quantum-number label, we identify that phase and follow a single vacancy through it. The total spin collapses directly from $S=L/4$ to $S=0$, with no partially polarized window. The singlet phase is critical: its singlet--triplet gap closes as $1/L$, its entanglement entropy grows logarithmically with a central charge $c\\simeq1.8$, and its modulation wavevector, extrapolated from $L=80$ to $200$, is commensurate at $3π/4$ and independent of $J_2$ to $5\\times10^{-5}$. Removing the central $S=1$ site switches the ground state of the doped chain from a triplet to a singlet at $J_2^{\\ast}=0.3068(3)$, where the host shows no feature; the triplet is not bound to the vacancy but spread over one of the two segments it leaves. The transmission of correlations through the vacancy saturates at a finite value below $J_2^{\\ast}$, $T(\\infty)=0.102(15)$ and $0.036(9)$ at $J_2=0.28$ and $0.30$, and the cut-chain law $T\\propto L^{-1}$ is excluded on both sides. We also show that the longitudinal correlator is not an observable in a triplet sector.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.22140",
  "author_total": 3,
  "authors": [
    {
      "name": "R. L. Silva"
    },
    {
      "name": "R. C. Silva"
    },
    {
      "name": "A. R. Pereira"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/c4ap2qwnz7b9k.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.22140",
  "fulltext_url": null,
  "id": "c4ap2qwnz7b9k",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.22140",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "cond-mat.stat-mech"
    ],
    [
      "arxiv",
      "cond-mat.str-el"
    ],
    [
      "openalex",
      "3104|Advanced Condensed Matter Physics"
    ]
  ],
  "openalex": "W7222469926",
  "pdf_url": "https://arxiv.org/pdf/2610.22140",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-15",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/c4ap2qwnz7b9k.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:29:50Z",
      "native_id": "2610.22140",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.22140"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.str-el",
      "subfield": "condensed-matter"
    },
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.stat-mech",
      "subfield": "statistical-nonlinear"
    }
  ],
  "title": "A rigid commensurate host and a defect that switches: vacancies in the frustrated alternating spin-(1, 1/2) Heisenberg chain",
  "title_text": "A rigid commensurate host and a defect that switches: vacancies in the frustrated alternating spin-(1, 1/2) Heisenberg chain",
  "type": "preprint",
  "updated_at": "2026-10-30T12:29:50Z",
  "url": "https://research.draconitic.com/paper/c4ap2qwnz7b9k",
  "venue": "arXiv",
  "versions": []
}