@article{21547,
  abstract     = {Flatbands have become a cornerstone of contemporary condensed-matter physics
and photonics. In electronics, flatbands entail comparable energy bandwidth and
Coulomb interaction, leading to correlated phenomena such as the fractional
quantum Hall effect and recently those in magic-angle systems. In photonics, they
enable properties including slow light1 and lasing2. Notably, flatbands support
supercollimation—diffractionless wavepacket propagation—in both systems3,4.
Despite these intense parallel efforts, flatbands have never been shown to affect the
core interaction between free electrons and photons. Their interaction, pivotal for
free-electron lasers5, microscopy and spectroscopy6,7, and particle accelerators8,9,
is, in fact, limited by a dimensionality mismatch between localized electrons and
extended photons. Here we reveal theoretically that photonic flatbands can overcome
this mismatch and thus remarkably boost their interaction. We design flatband
resonances in a silicon-on-insulator photonic crystal slab to control and enhance the
associated free-electron radiation by tuning their trajectory and velocity. We observe
signatures of flatband enhancement, recording a two-order increase from the
conventional diffraction-enabled Smith–Purcell radiation. The enhancement enables
polarization shaping of free-electron radiation and characterization of photonic
bands through electron-beam measurements. Our results support the use of
flatbands as test beds for strong light–electron interaction, particularly relevant for
efficient and compact free-electron light sources and accelerators.},
  author       = {Yang, Yi and Roques-Carmes, Charles and Kooi, Steven E. and Tang, Haoning and Beroz, Justin and Mazur, Eric and Kaminer, Ido and Joannopoulos, John D. and Soljačić, Marin},
  issn         = {1476-4687},
  journal      = {Nature},
  pages        = {42--47},
  publisher    = {Springer Nature},
  title        = {{Photonic flatband resonances for free-electron radiation}},
  doi          = {10.1038/s41586-022-05387-5},
  volume       = {613},
  year         = {2023},
}