Topological optical and phononic interface mode by simultaneous band inversion

Band inversion in one-dimensional superlattices is a strategy to generate topological interface modes in electronics, optics, acoustics, and nanophononics. Despite their potential for the control of topologically robust interactions, most realizations of these states have so far explored only a single kind of excitation. In this work, we design and fabricate GaAs/AlAs devices with simultaneously inverted band structures for light and phonons. We experimentally observe colocalized interface modes for 1.34 eV photons by optical reflectivity and 18 GHz phonons by coherent phonon generation and detection. Through numerical simulations, we demonstrate the ensuing robustness of the Brillouin interaction between them with respect to a specific type of disorder. Furthermore, we theoretically analyze the efficiency of time-domain Brillouin scattering in different topological designs presenting colocalized states and deduce a set of engineering rules. Potential future applications include the engineering of robust optomechanical resonators in a material system compatible with active media such as quantum wells and quantum dots.