{
  "abstract": "Optical second-harmonic generation (SHG) is a powerful probe of ferroelectric order, yet its microscopic origin and dynamical control are often understood primarily from symmetry considerations rather than from the underlying electronic processes. Here, we develop a microscopic theory of terahertz-controlled optical SHG in displacive ferroelectrics, establishing a direct connection between THz-driven polar lattice distortions and the resulting electronic nonlinear optical response. Starting from a complete Bloch-band representation, we show that an inversion-breaking lattice distortion reconstructs electronic Bloch wave functions, modifies optical dipole matrix elements, and activates nonlinear optical pathways that are forbidden in the centrosymmetric structure. We derive the second-order susceptibility in terms of the distortion-induced reconstruction of electronic states and optical transition matrix elements, and demonstrate that the electronic SHG susceptibility is linear in the polar distortion, $χ^{(2)}({\\bf Q})\\propto{\\bf Q}$, leading to an SHG intensity quadratic in the inversion-breaking order parameter. When the polar mode is coherently driven by a terahertz electric field, the resulting time-dependent lattice distortion dynamically reconstructs the electronic states and thereby modulates the optical SHG response, with $I_{2ω}(t)\\propto|{\\bf Q}(t)|^2$ to leading order. This framework distinguishes the THz-driven lattice dynamics from the electronic interband processes responsible for optical SHG, which is particularly important in insulating ferroelectrics where low-energy carrier dynamics are absent. Our theory thus provides a microscopic bridge between nonequilibrium polar lattice dynamics and ultrafast electronic nonlinear optics.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2608.30665",
  "author_total": 4,
  "authors": [
    {
      "name": "Hong-Kui Liu"
    },
    {
      "name": "Zi-Chen Qin"
    },
    {
      "name": "Jun-Song Wu"
    },
    {
      "name": "Yue Yuan"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/6bvcm22m324gg.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2608.30665",
  "fulltext_url": null,
  "id": "6bvcm22m324gg",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2608.30665",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "cond-mat.mtrl-sci"
    ],
    [
      "openalex",
      "2505|Ferroelectric and Piezoelectric Materials"
    ]
  ],
  "openalex": "W7204954429",
  "pdf_url": "https://arxiv.org/pdf/2608.30665",
  "pmcid": null,
  "pmid": null,
  "published": "2026-08-31",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/6bvcm22m324gg.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:41Z",
      "native_id": "2608.30665",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2608.30665"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.mtrl-sci",
      "subfield": "condensed-matter"
    }
  ],
  "title": "Terahertz Control of Optical Second-Harmonic Generation in Displacive Ferroelectrics: Electronic Bloch-State Reconstruction",
  "title_text": "Terahertz Control of Optical Second-Harmonic Generation in Displacive Ferroelectrics: Electronic Bloch-State Reconstruction",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:41Z",
  "url": "https://research.draconitic.com/paper/6bvcm22m324gg",
  "venue": "arXiv",
  "versions": []
}