Intrinsic and extrinsic mirror symmetry breaking in anti-dot spin-wave waveguides

We theoretically study the spin-wave spectra in magnonic waveguides periodically patterned with square anti-dots in nanoscale with pinned magnetization at the edges. We show that the breaking of the mirror symmetry of the waveguide by the structural changes can result in a magnonic band gap closing. These intrinsic symmetry breaking can be compensated by properly chosen asymmetric external bias magnetic field, i.e. in an extrinsic way. As a result the magnonic gaps existing in the ideal symmetric structure can be recovered. The model used for the explanation also suggests that this idea could be generic both for exchange and dipolar interaction regimes of spin-waves and also for other types of waves, e.g., electrons in the graphene ribbons.