Topological and non-reciprocal phenomena in elastic waves and heat transport of phononic systems

Abstract

Phonon is a quasi-particle excitation after the second quantization of lattice vibration. In the phonon framework, we can describe mechanics, elastic wave and thermal phenomena in solid uniformly. With the development of our understanding about solid state systems, phonon has become an important method to control device in solid state, which can be seen as a supplement and replacement for electronics and photonics. Among them, the modulation of elastic wave and heat conduction in phonon system has great theoretical and practical value. Elastic wave as an information carrier has the potential to construct new chip elements, while manipulating thermal phonon as an energy carrier can achieve the goal of energy transformation and device optimization. These fields have developed rapidly in recent years. A large number of novel materials such as thermal diodes, elastic meta-materials, thermal meta-materials, and heat pumping devices have been predicted and obtained. These developments are inseparable from the application of the concept of "topology" to phonon systems and the realization of non-reciprocal devices on various scales. In this paper, the topological and nonreciprocal phenomena in phonon systems are tentatively summarized. Besides, the latest research results are introduced and the development trend is prospected. The non-reciprocity of elastic wave and heat flow realized by time-dependent driving is reviewed with emphasis. This method has a great flexibility and can be similarly applied to multi-component systems on all scales.