Observation of light-induced Haldane gap in graphene

@misc{wang2026observation,
  title = {{Observation of light-induced Haldane gap in graphene}},
  author = {Fei Wang and Xuanxi Cai and Wanying Chen and Xiao Tang and Jinze Li and Benshu Fan and Tianshuang Sheng and Jinxi Lu and Jiansong Li and Hongyun Zhang and Pu Yu and Peizhe Tang and Wenhui Duan and Angel Rubio and Zhiyuan Sun and Shuyun Zhou},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.42115},
  eprint = {2610.42115},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.42115},
}

TY  - UNPB
TI  - Observation of light-induced Haldane gap in graphene
AU  - Fei Wang
AU  - Xuanxi Cai
AU  - Wanying Chen
AU  - Xiao Tang
AU  - Jinze Li
AU  - Benshu Fan
AU  - Tianshuang Sheng
AU  - Jinxi Lu
AU  - Jiansong Li
AU  - Hongyun Zhang
AU  - Pu Yu
AU  - Peizhe Tang
AU  - Wenhui Duan
AU  - Angel Rubio
AU  - Zhiyuan Sun
AU  - Shuyun Zhou
PY  - 2026
DA  - 2026/10/30
PB  - arXiv
DO  - 10.48550/arxiv.2610.42115
UR  - https://arxiv.org/abs/2610.42115
AB  - Symmetry and topology, encoded in electronic wavefunctions, play a central role in the electronic properties and emergent phenomena of quantum materials. While these properties are conventionally determined by the equilibrium Hamiltonian, strong optical fields offer a fundamentally different route by reshaping the Hamiltonian on ultrafast timescales, turning symmetry and topology into dynamically controllable degrees of freedom. Graphene provides a paradigmatic platform for realizing this concept, where circularly polarized light has long been predicted to dynamically break time-reversal symmetry (TRS) and open a topologically nontrivial gap at the Dirac point. Despite extensive experimental efforts, direct observation of this Dirac gap-the defining spectroscopic signature of the dynamical TRS-breaking induced topological phase-has remained missing. Here we directly observe this light-induced Dirac gap in monolayer graphene. Time- and angle-resolved photoemission spectroscopy reveals that the gap emerges simultaneously with the optical field and exclusively under circularly polarized driving, directly linking its opening to dynamical TRS breaking. Together with Floquet theory, we identify the gap with a light-induced Haldane mass and reveal the associated nontrivial Floquet Berry curvature and Chern topology. By demonstrating dynamical TRS breaking in a prototypical non-magnetic material, our results establish optical driving as a route to ultrafast engineering of symmetry and topology, opening opportunities for dynamically tunable quantum matter beyond equilibrium.
ER  -