Nontrivial point-gap topology and non-Hermitian skin effect in photonic crystals

We show that two-dimensional non-Hermitian photonic crystals made of lossy material can exhibit non-trivial point gap topology in terms topological winding its complex frequency band structure. Such be either isotropic media which is reciprocal, or magneto-optical non-reciprocal. discuss the effects reciprocity on properties topology. also such a leads to skin effect when crystal truncated. In contrast most previous studies used tight-binding models, our work indicates studied crystals, represent more realistic system has technological significance.