Demonstration of phase transitions using a 1D longitudinal mechanical topological insulator

We constructed a mechanical model of a metallic spring to demonstrate the properties of a one-dimensional Su-Schrieffer-Heeger (SSH) model of topological insulators. In our model, the spring propagates longitudinal waves and was shown to demonstrate phase transitions between the insulator, conductor, and topological insulator phases of the SSH model. The former was done by changing the spring constant between atoms within sites. A clear edge state was also shown in the topological insulator phase. In addition, these findings are supported by a mathematical model derived from the mechanics of harmonic oscillators. Our device is simple to construct and easy to understand. It is a great tool to demonstrate an important aspect of condensed-matter physics research to undergraduate students.