Observation of Topological Nodal-Ring Phonons in Monolayer Hexagonal Boron Nitride

TL;DR

This paper provides experimental evidence of topological nodal-ring phonons in monolayer hexagonal boron nitride, revealing new 2D topological phononic states beyond graphene, with potential applications in electronics and photonics.

Contribution

It reports the first experimental observation of topological phonons in monolayer hexagonal boron nitride, expanding the scope of 2D topological phononics beyond graphene.

Findings

Identification of two topological nodal rings in hBN

Protection of nodal rings by mirror symmetry

Potential for phononic device applications

Abstract

Topological physics has evolved from its initial focus on fermionic systems to the exploration of bosonic systems, particularly phononic excitations in crystalline materials. Two-dimensional (2D) topological phonons emerge as promising candidates for future technological applications. Currently, experimental verification of 2D topological phonons has remained exclusively limited to graphene, a constraint that hinders their applications in phononic devices. Here, we report experimental evidence of topological phonons in monolayer hexagonal boron nitride using advanced high-resolution electron energy loss spectroscopy. Our high-precision measurements explicitly demonstrate two topological nodal rings in monolayer hexagonal boron nitride, protected by mirror symmetry, expanding the paradigm of 2D topological phonons beyond graphene. This research not only deepens fundamental understanding of 2D topological phonons, but also establishes a phononic device platform based on wide-bandgap insulators, crucial for advancements in electronics and photonics applications.