HKBU's Collaborative Research Experimentally Demonstrates a Special Type of Third-order Exceptional Lines and Reveals their Topological Properties

Exceptional lines in a three-dimensional parameter space and its acoustic realization.

A collaborative research team co-led by Prof. Guancong Ma from the Department of Physics, Hong Kong Baptist University and Prof. Kun Ding from the Department of Physics, Fudan University has experimentally realized the order-3 exceptional lines (EL3) in a stack of three coupled acoustic cavities. 

The reported EL3 are embedded in an order-2 exceptional surface. Such geometry presents an unexpected difficulty in investigating the topological properties of EL3 with the prevailing topological characterization methods. To address this challenge, a winding number associated with the resultants of the Hamiltonian matrix was introduced. This resultant winding number can be chosen to detect only the EL3 but ignores the ES2, allowing the diagnosis of the topological currents carried by the EL3. The research team also generalizes the approach for detecting and studying the topological properties of higher-order EPs. The reported outcomes exemplify the unprecedented topology of higher-order exceptional geometries and may inspire new non-Hermitian topological applications. 

The findings of this research were published in Nature Communications, and the title of the publication is “Realization and Topological Properties of Third-Order Exceptional Lines Embedded in Exceptional Surfaces.”