A comparison study between topological insulators based on valley Hall and quantum spin Hall effects

Abstract

Over the past few years, the rapid development in the fields of condensed matter physics, electronic and photonic systems have inspired the design and experimental demonstration of various acoustic topological insulators. Among these, the topologically protected one-way propagation is a phenomenon that is gaining increased attention. Pseudospin states, which is the analogue of the Quantum Spin Hall Effect from electronic systems, has been proven to enable topological edge states in acoustics. Similarly, Valley Hall (VH) effect is also observed in acoustic systems and provides a pair of valley vortex states with opposite chirality. These valley vortex states can similarly form topologically protected edge states and in turn realize robust one-way propagation. However, the differences in the physics behind these acoustic systems give rise to distinct features such as angle selection and immunization level to various types of defects. In this article, the comparison between topological insulators (TI) and valley hall topological insulators (VHTI) address the difference and similarities in several aspects. Both of them have topologically protected bandgaps and thus the robust one-way propagation. For the maximum transmission incident angle and defect immunization, however, VH topological waveguide and TI waveguide show different characteristics.