Topological optical and phononic interface mode by simultaneous band inversion

Abstract

Interface modes have been widely explored in the field of electronics, optics, acoustics and nanophononics. One strategy to generate them is band inversion in one-dimensional superlattices. Most realizations of this type of topological states have so far been explored for a single kind of excitation. Despite its potential in the manipulation and engineering of interactions, platforms for the simultaneous topological confinement of multiple excitations remain an open challenge. GaAs/AlAs heterostructures exhibit enhanced optomechanical interactions due to the intrinsic colocalization of light and sound. In this work, we designed, fabricated, and experimentally studied a multilayered structure based on GaAs/AlAs. Due to the simultaneously inverted band structures for light and phonons, colocalized interface modes for both 1.34 eV photons and 18 GHz phonons appear. We experimentally validated the concept by optical reflectivity and coherent phonon generation and detection. Furthermore, we theoretically analyzed the performance of different topological designs presenting colocalized states in time-domain Brillouin scattering and deduce engineering rules. Potential future applications include the engineering of robust optomechanical resonators, compatible with the incorporation of active media such as quantum wells and quantum dots.

Simultaneous confinement of acoustic phonons and near infrared photons in GaAs/AlAs multilayers by band inversion

“…Based on the band inversion concept applied to an optophononic GaAs/AlAs heterostructure, we theoretically propose and experimentally demonstrated an interface mode where both near infrared photons and gigahertz phonons are simultaneously confined. 10 In the conception of simultaneous optical-acoustic topological interface states, the local density of states of two excitations can be engineered and controlled simultaneously. As such, topological engineering can be performed not only on the individual excitations but also on their interactions, taking advantage of different robustness characteristics.…”

“…As such, topological engineering can be performed not only on the individual excitations but also on their interactions, taking advantage of different robustness characteristics. 10 Finally, the concept of colocalization can be extended to 3D micropillars. [53][54][55][56][57] Since GaAs/AlAs heterostructures are widely used in optoelectronics and photonics, 58,59 the engineering of acoustic phonons becomes directly accessible in existing structures.…”

“…Because of a remarkable coincidence in the physical parameters governing light and acoustic phonon propagation in these two materials, the equations for both longitudinal acoustic waves and normal-incidence light become practically equivalent for excitations of the same wavelength. 7,9,10 This coincidence guarantees spatial overlap between the electromagnetic and displacement fields of specific photon-phonon energy pairs, leading to strong lightmatter interactions 9 and enabling nanoacoustics as a powerful ingredient in designing a plethora of optical and optoelectronic devices based on these materials.…”

Probing gigahertz coherent acoustic phonons in TiO2 mesoporous thin films

“…Among other applications, they are suitable for high resolution nanoimaging, non-destructive testing, and sensing. Acoustic phonon dynamics have been explored in systems such as plasmonic nanostructures, [10] , [11] , [12] , [13] metasurfaces, [14] oxides, [15] , [16] , [17] , [18] and semiconductor heterostructures [19] , [20] , [21] , [22] with layer thicknesses on the nanometric scale [19] , [23] , [24] . To precisely tailor the nanophononic response and obtain high quality devices, expensive and complex growth and processing techniques are usually employed, including molecular beam epitaxy and electron beam lithography.…”

Terahertz cavity optomechanics using a topological nanophononic superlattice

“…The phonons and photons both can be confined in the cavity. 21 In our work, the mechanical topological interface state, which is protected against any perturbation that does not change the underlying topological invariants of the structures, 29 at the terahertz frequency was obtained by concatenating two GaAs/AlAs superlattices with inverted spatial mode symmetries at the band edges around a common minigap, without a mechanical resonant spacer. The topological invariants (Zak phases) corresponding to the two concatenated systems determine the existence of an interface mode confined between them.…”