Electrically tunable magnonic bound states in the continuum

Low-energy excitations of a magnetically ordered system are spin waves with magnon being their excitation quanta. Magnons are demonstrated to be useful for data processing and communication. To achieve magnon transport across extended distances, it is essential to minimize magnonic dissipation which can be accomplished by material engineering to reduce intrinsic damping or by spin torques that can counteract damping. This study introduces an alternative methodology to effectively reduce magnon dissipation based on magnonic bound states in the continuum (BIC). We demonstrate the approach for two antiferromagnetically coupled magnonic waveguides, with one waveguide being attached to a current carrying metallic layer. The current acts on the attached waveguide with a spin-orbit torque effectively amplifying the magnonic signal. The setup maps on a non-Hermitian system with coupled loss and more loss, enabling the formation of dissipationless magnon BIC. We investigate the necessary criteria for the formation of magnon BIC through electric currents. The influences of interlayer coupling constant, anisotropy constants, and applied magnetic field on the current-induced magnon BIC are analyzed. The identified effect can be integrated in the design of magnon delay lines, offering opportunities for the enhancement of magnonic devices and circuits.