{
  "abstract": "Extreme stiffness contrasts between loading modes usually require architected metamaterials with compliant hinges, whereas covalent crystals rarely exhibit such behavior intrinsically. Here, density functional theory calculations of the complete in-plane elastic tensors of four tetragonal carbon monolayers reveal a more than 50-fold spread in shear stiffness, despite less than a twofold variation in axial stiffness and the same symmetry-allowed tensor form. Twin T-graphene shows the strongest contrast: its shear constant, $C_{66}=3.03$~N m$^{-1}$, is 47 times smaller than in graphene and yields a shear Kelvin eigenvalue 29 times below the two normal-strain eigenvalues, while the Born stability criteria hold. This shear constant revises an earlier inference of elastic isotropy based on normal strains alone. Constrained relaxations and symmetry-resolved mode analysis identify the mechanism as a $B_{2g}$ counter-torsion of the carbon sublayers about the mid-plane bonds, which removes 96.3% of the clamped-ion shear stiffness with bond-length changes below 0.15%. An internal-coordinate model quantifies this cancellation, identifying internal relaxation, rather than weak bonding, as the origin of the soft channel. The resulting anisotropy predicts transverse sound velocities of 1.95 km s$^{-1}$ along [100] and 10.62 km s$^{-1}$ along [110], a testable acoustic signature. Phonon calculations, ab initio molecular dynamics at 300 K, and large-deformation simulations indicate that the soft channel is dynamically stable, preserves the local bonding, and persists beyond the harmonic regime. Our results show how bonding topology enables extreme mode-selective elasticity through internal relaxation in a mechanically stable covalent crystal.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.19168",
  "author_total": 3,
  "authors": [
    {
      "name": "J. W. González"
    },
    {
      "name": "M. Pacheco"
    },
    {
      "name": "J. D. Correa"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7kpt1b01mt08q.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.19168",
  "fulltext_url": null,
  "id": "7kpt1b01mt08q",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.19168",
  "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.mtrl-sci"
    ],
    [
      "openalex",
      "2505|Graphene research and applications"
    ]
  ],
  "openalex": "W7222326147",
  "pdf_url": "https://arxiv.org/pdf/2610.19168",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-26",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7kpt1b01mt08q.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:35:35Z",
      "native_id": "2610.19168",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.19168"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.mtrl-sci",
      "subfield": "condensed-matter"
    }
  ],
  "title": "Symmetry-selected extreme shear compliance in a stable carbon monolayer",
  "title_text": "Symmetry-selected extreme shear compliance in a stable carbon monolayer",
  "type": "preprint",
  "updated_at": "2026-10-30T12:35:35Z",
  "url": "https://research.draconitic.com/paper/7kpt1b01mt08q",
  "venue": "arXiv",
  "versions": []
}