Bi-reflection of spin waves by magnon-phonon hybridization

When a light wave propagates into the different media with an optical anisotropy, the refracted light wave splits into two depending on the polarization of the light, a phenomenon called birefringence. On the other hand, when a light wave reflects at a boundary, reflected beam is usually single ray and forms the same angle with the incident angle, a famous law of reflection. We report a split of the reflected magnetic spin waves as a result of reflection with the aid of magnon-phonon hybridization. Spin waves, collective precession of magnetic moments propagating as waves, couple with phonons via spin-orbit interaction, which is strong enough to create a new normal state, i.e. magnon-phonon hybridized waves. The hybridized wave inherits the properties of phonons, leading to abnormal reflection dynamics. In this talk, we report the result of time-resolved magneto-optical microscopy of the reflection dynamics of the hybridized waves. Our experimental results and theoretical modeling demonstrate that the mode degree of freedom of phonon is transferred to spin waves via the hybridization.