{
  "id": "1707.05522",
  "version": "v1",
  "published": "2017-07-18T08:36:46.000Z",
  "updated": "2017-07-18T08:36:46.000Z",
  "title": "Quantum phase transitions in effective spin-ladder models for graphene zigzag nanoribbons",
  "authors": [
    "Cornelie Koop",
    "Stefan Wessel"
  ],
  "comment": "12 pages, 15 figures",
  "categories": [
    "cond-mat.mes-hall",
    "cond-mat.str-el"
  ],
  "abstract": "We examine the magnetic correlations in quantum spin models that were derived recently as effective low-energy theories for electronic correlation effects on the edge states of graphene nanoribbons. For this purpose, we employ quantum Monte Carlo simulations to access the large-distance properties, accounting for quantum fluctuations beyond mean-field-theory approaches to edge magnetism. For certain chiral nanoribbons, antiferromagnetic inter-edge couplings were previously found to induce a gapped quantum disordered ground state of the effective spin model. We find that the extended nature of the intra-edge couplings in the effective spin model for zigzag nanoribbons leads to a quantum phase transition at a large, finite value of the inter-edge coupling. This quantum critical point separates the quantum disordered region from a gapless phase of stable edge magnetism at weak intra-edge coupling, which includes the ground states of spin-ladder models for wide zigzag nanoribbons. To study the quantum critical behavior, the effective spin model can be related to a model of two antiferromagnetically coupled Haldane-Shastry spin-half chains with long-ranged ferromagnetic intra-chain couplings. The results for the critical exponents are compared also to several recent renormalization group calculations for related long-ranged interacting quantum systems.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-07-18T08:36:46.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "quantum phase transition",
      "graphene zigzag nanoribbons",
      "effective spin-ladder models",
      "effective spin model",
      "quantum monte carlo simulations"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 12,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}