How to steer the nanlight in ‘forbidden’ directions

The development of the future photonic nanotechnologies in communications and biological sensors is ultimately dependent on our ability to control the spread of nano-light in nano-sized optical circuits (10,000 times smaller than the thickness of a human hair).

Now scientists from the University of Oviedo, the Center for Research in Nanomaterials and Nanotechnology (CINN-CSIC), the Donostia International Physics Center (DIPC), the Moscow Institute of Physics and Technology of Russia and the Austrian Institute of Technology have achieved a milestone in being able to guide the nanlight along directions hitherto forbidden in a nanometer-thick material.

A milestone has been achieved by guiding the nanlight along directions that until now could not be done in a nanometer-thick material.

The finding, published in the journal Science Advances, has applications in information processing, telecommunications, sensors and heat control on the nanometer scale.

The authors have demonstrated this finding in a van der Waals material that can be divided into sheets a few atoms thick, like a pack of folios that are easily separated. The best known is graphene, but there are many others that are currently being investigated for their unique properties. Some allow the propagation of the nanlight or polaritons, electromagnetic waves that are excited when illuminating the material and propagate on its surface in a similar way to waves in the sea.

Molybdenum trioxide

Molybdenum trioxide, another van der Waals material, has been used in this work. Contrary to what happens in conventional materials where the nanlight can propagate in all directions, in molybdenum trioxide this tiny light can only propagate along specific directions, while it cannot in others.

This exotic ability to guide nanolights directionally has very interesting applications in fields as diverse as biosensing, telecommunications and, therefore, the possibility of controlling this direction of propagation on demand would open up endless new possibilities.

The advance has been achieved by coupling the nanolight in molybdenum trioxide with substrates such as silicon carbide, visualizing the phenomenon with a scanning optical microscope.

What the team has now discovered is that it is possible to reorient the propagation of nanlight along these previously forbidden directions, coupling said nanlight in molybdenum trioxide with certain substrates, such as silicon carbide.

The experiments were carried out by direct visualization of the phenomenon using a near-field scanning optical microscope, one of the most advanced methods in the investigation of new nanomaterials.

“Our experiments far exceeded our expectations,” says co-author. Jiahua duan, postdoctoral researcher in the Quantum Nano-optics group at the University of Oviedo. “By superimposing molybdenum trioxide on silicon carbide, we saw that we could send the nanlight along forbidden directions.”

Importance of topology

“When we studied it, we realized that it had a lot to do with a mathematical property: topology,” he adds. Gonzalo alvarez perez, PhD student in the same group. “This fact provides new fundamental knowledge about nanlight in highly anisotropic materials and, although this work is based on specific materials and a specific spectral range, it lays the foundations to be able to extend these unusual optical characteristics to other systems.”

The study shows that structures composed of sheets of van der Waals materials provide significant functionalities in the emerging field of nano-optics.

“Our finding in this material has important implications in the development of future information and communication technologies, since it can be used as a router, allowing us to guide the propagation of nanlight along the desired direction”, he points out. Javier Martin Sanchez, Ramón y Cajal researcher in the Quantum Nano-optics group.

“This work provides new fundamental insights into the emergence of topological transitions in van der Waals materials, which constitute an ideal platform for translating recent advances in electronic materials topology into optics, a very promising route to direct light efficiently at the nanoscale. “, stands out for its part Alexey Yu Nikitin, Ikerbasque researcher at the DIPC.

According to the authors, this study shows that structures composed of sheets of van der Waals materials provide significant functionalities in the emerging field of nano-optics. Pablo Alonso González, leader of the Quantum Nano-optics group, explains that “the possibility of guiding the propagation of light at the nanoscale along new directions will allow the development of applications in biological sensors, quantum technologies or the use of heat in the nanoscale “.


Jiahua Duan, Gonzalo Álvarez-Pérez, Kirill. V. Voronin, Iván Prieto, Javier Taboada-Gutiérrez, Valentyn S. Volkov, Javier Martín-Sánchez, Alexey. Y. Nikitin and Pablo Alonso-González, “Enabling propagation of anisotropic polaritons along forbidden directions via a topological transition.” Science Advances, 2021.

Rights: Creative Commons.