The control of coherent phenomena in graphene structures is proposed. Specifically, plasmon induced transparency (PIT) effect is investigated in a kind of simple graphene structures - graphene ribbon pairs. The transparency effect are understood by the mode coupling between dipolar and quadrupole plasmons modes in graphene ribbons. By using bias voltage tuning or geometry parameters changing, the PIT effect can be effectively controlled, which is based on the frequency tuning of dipolar or quadrupole modes in ribbons. These properties make these structures possess applications in two-dimensional plasmonics devices in mid-infrared range. In addition, the tuning of PIT in graphene ribbon pairs opens an avenue for active coherent control in plasmonics.

Ultrastrong coupling in the near-UV range between aluminum metal–insulator–metal cavities and CdZnS/ZnS quantum dots is revealed by using cathodoluminescence; at the same time, the plexcitonic modes are spatially mapped at the deep-subwavelength scale.

Using cathodoluminescence, the plasmonic modes of open triangle cavities patterned in single-crystal bulk aluminum are explored in deep subwavelengths from the UV to the visible, showing large Q factors.

Spectral resolving and imaging surface plasmon modes in noble metal nanostructures are important for applications in nanophotonics. Here, we use cathodoluminescence (CL) spectroscopy to excite and probe quasi-dark plasmon modes of Au nanoring cavities. Numerical simulations of both the spectra and the electromagnetic field distribution are carried out by using boundary element method. Good agreement between the experimental and simulated results is obtained. Particularly, CL is shown as an efficient method to probe quadrupole modes, which is difficult for traditional optical means. Moreover, a high Purcell factor in excess of 100 is obtained for the dark quadrupole modes in gold ring cavities. Our work provides an efficient way to explore the initial nature of surface plasmon modes in metal nanostructures.

Aluminum (Al) has prominent material and plasmonic properties in the ultraviolet (UV) spectral range. However, the large losses of plasmon antennas with multicrystal Al is the bottleneck for plasmonic applications.Here, the plasmon properties of single-crystal and multicrystal Al nanostructures are compared. In the platform of bulk single-crystal Al, spatially and spectrally resolved cathodoluminescence (CL) spectroscopy is used to excite and image the plasmonic modes of I-shaped and cross-shaped nanoridge antennas. The evolution and coupling of plasmon modes at the nanoscale are clearly observed in these antennas. Plasmon modes for I-shaped antennas can be exactly understood from the standing waves of the propagating plasmons in Al nanoridge waveguides. Moreover, the plasmon response of cross-shaped antennas is determined by the two different standing wave paths. The experimental results agree well with full wave electromagnetic simulations. Our results lay a foundation for the design of more complex and efficient optical antennas with single-crystal Al, which have great potential applications in UV plasmonics, such as fluorescence enhancement or biosensing.