Recently, the team led by Prof. ZENG Changgan from the University of Sciences and Technology of China (USTC) of the Chinese Academy of Sciences, collaborating with LI Xiaoguang's team from Shenzhen University, has enabled the remote tuning of the lifetime of coupled plasmon excitations by designing and introducing an additional damping pathway through adjusting the Fermi energy level of graphene, and the damping tuning system has been elucidated in conjunction with theory. The study was published in Physical Review Letters as an Editors' Suggestion.  

The quasiparticle concept is vital in condensed matter physics. The interaction of light with matter can form quasiparticles such as plasmons, excitons, and phonon polaritons. These quasiparticles show a wealth of physical properties and applications, including plasmonic metamaterials, exciton Bose-Einstein condensation, and nanoacoustic resonators, and a suitable lifetime is a prerequisite for the rich physical properties of the quasiparticles to be detected and translated into practical applications.  

Therefore, a lot of effort has been devoted to the investigation of the damping mechanism of quasiparticles and the systems with intrinsically optimal lifetimes. Exploration of active modulation of quasiparticle lifetimes is another critical research field, which deals with the application of quasiparticle-related systems. 

In this study, the researchers carried out a systematic study of coupled Dirac plasmon excitations in graphene/BN/graphene heterostructure by adopting scattering-type scanning near-field optical microscopy and the random-phase approximation method, and achieved multi-dimensional modulation of the coupled plasmons. 

Due to Coulomb interactions, the plasmon excitons of the two graphene layers form an optical coupling pattern with longer wavelengths and higher intensities through long-range coupling. Significant adjustments in wavelength and intensity can be achieved by varying parameters such as carrier density and interlayer spacing. More importantly, the lifetime of the coupled plasmon can be remotely modulated by electric field-controlled damping pathways.  

Besides, the researchers exploited the Dirac linear dispersion of graphene and designed one layer of graphene as a damping modulator, allowing them to regulate the quasiparticle lifetime by opening and closing the damping pathway by changing its Fermi energy level. 

The work designs a prototype device for nanophotonics and provides fresh concepts for the active control of other quasiparticle lifetimes.