Edge solitons in non-Hermitian photonic lattices with type-II Dirac cones

An edge soliton is a localized bound state that arises from the balance between diffraction broadening and nonlinearity-induced self-focusing. It typically resides either at the edge or at the domain wall of a lattice system. To the best of our knowledge, most reported edge solitons have been observed in conservative Hermitian systems; whether stable edge solitons can exist in non-Hermitian systems remains an open question. In this work, we utilize a photonic lattice that naturally exhibits type-II Dirac cones and introduce a domain wall by carefully configuring gains and losses at the three sites within each unit cell. Surprisingly, edge states localized at the domain wall can exhibit entirely real propagation constants. Building on these edge states, we demonstrate the existence of edge solitons that can propagate stably over distances significantly exceeding those in the experimental settings adopted in this study. Although these solitons eventually couple with the bulk states and ultimately collapse, they exhibit remarkable resilience. Our findings establish that a domain wall supporting loss-resistant edge solitons, which can also evade the skin effect, is achievable in non-Hermitian systems. This discovery holds promising potential for the development of compact functional optical devices.