Demonstration of a two-dimensional $${\cal P}{\cal T}$$PT-symmetric crystal

@article{Kremer2019DemonstrationOA,
  title={Demonstration of a two-dimensional \$\$\{\cal P\}\{\cal T\}\$\$PT-symmetric crystal},
  author={Mark Kremer and Tobias Biesenthal and Lukas J. Maczewsky and Matthias Heinrich and Ronny Thomale and Alexander Szameit},
  journal={Nature Communications},
  year={2019},
  volume={10},
  pages={1-7}
}
With the discovery of $${\cal P}{\cal T}$$PT-symmetric quantum mechanics, it was shown that even non-Hermitian systems may exhibit entirely real eigenvalue spectra. This finding did not only change the perception of quantum mechanics itself, it also significantly influenced the field of photonics. By appropriately designing one-dimensional distributions of gain and loss, it was possible to experimentally verify some of the hallmark features of $${\cal P}{\cal T}$$PT-symmetry using… 
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