Topologically Protected Localized State of Elastic Wave in a One-Dimensional Phononic Crystal

2018.08.03

Satoshi Iwamoto and Ingi Kim

Institute of Industrial Science, The University of Tokyo

Topological material science is now a blooming research area in condensed matter physics. Utilizing the concept of band topology, various new materials and new phases of matters have been discovered. They are expected to innovate the current electronic devices in various aspects. Recently, the concept has been introduced into the field of photonics, acoustics and elastics and open new paradigms in the related fields. We are promoting the researches aiming at the realization and application of topological states of light and of elastic wave using photonic and phononic crystals.
In the present work, we designed two one-dimensional phononic crystal possessing a common complete phononic bandgap but distinct band topology and succeeded in observing the topologically protected localized state of elastic wave formed at the interface between them. The sample made of fused silica was fabricated by using ultrasonic machining technique. The frequency of the localized elastic wave was ~200 kHz. We also spatially imaged the localized state by means of the photoelastic effect.
The paper reporting these results has been published in Appl. Phys. Express and was selected one of the spotlight papers of the journal. Miniaturizing the structure can increase the frequency of the state further. In addition, it will be also possible to realize topological elastic states in opto-mechanical crystals. There approaches would pave the way not only for efficient control of elastic waves but also for novel platform for hybrid optomechanical systems.