Orbital angular momentum in crystalline solids: non-equilibrium theory

@misc{sharma2026orbital,
  title = {{Orbital angular momentum in crystalline solids: non-equilibrium theory}},
  author = {Sangeeta Sharma and Peter Elliott and Samuel Shallcross},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.00496},
  eprint = {2610.00496},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.00496},
}

TY  - UNPB
TI  - Orbital angular momentum in crystalline solids: non-equilibrium theory
AU  - Sangeeta Sharma
AU  - Peter Elliott
AU  - Samuel Shallcross
PY  - 2026
DA  - 2026/10/01
PB  - arXiv
DO  - 10.48550/arxiv.2610.00496
UR  - https://arxiv.org/abs/2610.00496
AB  - We develop a general operator theory of orbital angular momentum (OAM) in periodic solids that applies equally to equilibrium and coherently driven states. Employing the crystal momentum representation of Adams and Blount, we construct a periodic-solid OAM operator exactly corresponding to the symmetrized r̂×v̂ observable, and show that it separates into local circulation (LC) and itinerant circulation (IC) sectors that are Hermitian and U(1), and more generally U(N), gauge covariant. In equilibrium, the LC and IC sectors reduce to the established modern theory of orbital magnetism; out of equilibrium, the same operator structure exposes new contributions generated by laser-written momentum-space textures and interband coherence. Applied to gapped graphene, we uncover a rich phenomenology of ultrafast non-equilibrium orbital angular momentum, including a quasi-stationary light-induced OAM. This latter finding, underpinned by a close connection between band-manifold phase texture and nonequilibrium OAM, points towards new possibilities for light control over OAM in solids as well as a potentially rich role for topological band structures in designed OAM materials.
ER  -