Recently, Professor Shi Zhiwen’s research team from Shanghai Jiao Tong University, in collaboration with other researchers, published a research paper entitled “Frequency-dependent topological polaritons in carbon nanotube array/hBN heterostructures” in Nature Communications. This study presents the observation of topological polaritons in heterostructures composed of carbon nanotube arrays and hexagonal boron nitride (hBN).

Surface polaritons are collective oscillation modes formed by the interaction of photons with particles such as electrons and phonons. These electromagnetic waves are confined to the material surface, allowing them to transcend the diffraction limit and achieve light manipulation at deeply subwavelength scales.

Through experiments, the research team achieved hybrid coupling between hyperbolic plasmon-polaritons in carbon nanotube arrays and phonon-polaritons in hexagonal boron nitride. They observed a topological transition of polaritons in this structure that depends on the excitation light frequency. When the excitation light frequency is far from the reststrahlen band of boron nitride, the plasmon-polaritons exhibit hyperbolic patterns. In contrast, when the excitation light frequency enters the reststrahlen band of boron nitride, the wavefront shapes of the plasmon-polaritons become elliptical. These two types of polaritons, with distinct topological shapes, propagate in completely different directions in terms of energy and momentum.

Furthermore, the research team also observed whispering gallery modes of coupled polaritons in a ring-shaped carbon nanotube array/hexagonal boron nitride structure. This discovery offers innovative concepts for future nano-optoelectronic integrated devices and provides a new platform for investigating light-matter interactions at the nanoscale.