A research team has discovered how to finely control Dirac plasmon polaritons in topological insulator metamaterials, overcoming long-standing challenges in the terahertz range.
In today’s world of advanced nanotechnology, the ability to control light at extremely small scales is essential for breakthroughs in faster data transfer, ultra-sensitive detection systems, and next-generation imaging technologies. At the heart of this frontier are Dirac plasmon polaritons (DPPs), unusual waves that combine light with the motion of electrons in ultra-thin, two-dimensional materials.
Unlike ordinary light waves, which are restricted by the natural speed of light in free space, DPPs have the ability to compress light into spaces up to one hundred times smaller than its original wavelength. This extraordinary capability makes them powerful tools for manipulating light at the nanoscale, far beyond the reach of conventional optics.
What sets DPPs apart is how they behave in Dirac materials such as graphene and topological insulators. In these materials, electrons move as though they are massless, giving DPPs remarkable flexibility. This characteristic makes them highly adaptable to environmental changes and positions them as key components for the future of nano-optoelectronic devices.
Their importance grows even further in the terahertz (THz) frequency range—a portion of the electromagnetic spectrum that lies between microwaves and infrared light. Often referred to as the “THz gap,” this range is one of the least explored areas in science and technology. Yet it holds enormous promise for applications including security screening, wireless communication, and advanced medical diagnostics. Despite this potential, effectively controlling light at THz frequencies has remained a persistent obstacle.
How DPPs Can Bridge the Gap
DPPs offer a solution. Because they can confine and guide THz waves at the nanoscale, they could lead to compact and efficient THz photonic components, such as detectors, modulators, and waveguides. The ability to tune and direct these waves opens the door to reconfigurable photonic circuits, with applications ranging from quantum technologies to ultra-fast computing.
In a new paper published in Light: Science & Applications, a team of scientists led by Prof. Miriam Serena Vitiello has developed a new method to precisely control the behavior of Dirac plasmon polaritons (DPPs)—collective oscillations of massless charge carriers—in two-dimensional materials, opening new possibilities for advanced nanophotonic technologies.
DPPs are critical for manipulating light at the nanoscale, but their high momentum and rapid signal loss at terahertz (THz) frequencies have made them difficult to harness.
Engineering Metamaterials for Precision
Now, a research team has demonstrated a novel approach using topological insulator metamaterials made from epitaxial Bi₂Se₃. By designing and fabricating laterally coupled nanostructures—called metaelements—with specific spacing, they were able to tune the wavevector of DPPs through geometric control.
Using advanced phase-sensitive near-field microscopy, the team successfully launched and imaged DPP propagation in these nanostructures.
The study revealed that adjusting the spacing between coupled metaelements could increase the polariton wavevector by up to 20% and extend the attenuation length by more than 50%.
“These findings represent a significant step toward the development of tunable THz optical devices with lower energy loss and enhanced performance. This breakthrough could open a new venue for THz nanophotonics, non-linear optics, and energy-efficient photovoltaic devices,” the scientists forecast.
Reference: “Tracing terahertz plasmon polaritons with a tunable-by-design dispersion in topological insulator metaelements” by Leonardo Viti, Chiara Schiattarella, Lucia Sichert, Zhengtianye Wang, Stephanie Law, Oleg Mitrofanov and Miriam S. Vitiello, 26 August 2025, Light: Science & Applications.
DOI: 10.1038/s41377-025-01884-0
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