Energy
Editorial of the Technological Innovation Website – 04/30/2024
Scanning electron microscope image of a “strained” photon crystal. The researchers effectively made light “sense” a magnetic field within the crystal’s complicated structure.
[Imagem: Rechtsman Laboratory/Penn State]
Interaction of light with magnetism
Scientists have for the first time managed to make light “feel” a magnetic field – unlike electrons, light particles have no charge, so they do not respond to magnetic fields.
To make light sensitive to magnetism, researchers created a complicated structure, of a type known as a photonic crystal, which is made of silicon and glass. Inside the crystal, the light rotates in circles forming discrete bands of energy, mimicking a well-known phenomenon observed in electrons.
This discovery could point to new ways of increasing the interaction of light with matter, an advance that has the potential to improve photonic technologies, enabling very small lasers and the long-awaited computing with light.
Interestingly, the long-awaited tool was developed and announced simultaneously by two teams, one from Pennsylvania State University, in the USA, and another from Delft Technical University, in the Netherlands, who worked independently.
The crystal creates discrete bands of energy for photons, like electrons normally have.
[Imagem: Maria Barsukova et al. – 10.1038/s41566-024-01425-y]
energy levels
The term electromagnetism does not hide the importance of the interaction between electric fields and magnetic fields, crucial for a countless number of technological applications. That’s why there has been great interest in reproducing the behavior of electrons using photons, which has the potential to, among many other examples, do everything we already do faster and using less energy.
When electrons are confined to a two-dimensional surface and exposed to a strong magnetic field, they move in circular orbits, or “cyclotrons.” The movement of these orbits becomes quantized, that is, the electrons are restricted to certain discrete energies, which are called Landau levels.
“Landau levels are similar to the energy levels of the electron orbitals around the nucleus of an atom,” explained Professor Mikael Rechtsman, leader of the North American team. “In an atom, energy levels result from the attraction of negatively charged electrons to the positively charged nucleus, while Landau levels result from the interaction of electrons with a magnetic field. We employ a method of emulating a magnetic field – called a pseudomagnetic field – to light, precisely manipulating the structure of a photonic crystal.”
Photomagnetic interaction
The crystal is made of silicon, the same used to make chips. The difference is that, instead of using lithography to make transistors, grooves and holes were created to create a network with a honeycomb-like structure. To mimic the effects of a magnetic field, the researchers used another superimposed crystal to add “tension” to the lattice pattern.
When light hits the photon crystal, it spreads evenly. However, in the tensioned network, light moves in circles and its energy spectrum changes, forming discrete bands, just like Landau levels. Unlike the Landau levels in electrons, the energy bands of light are not flat, they are curved. But this curvature was corrected by making modifications to the photonic crystal lattice itself.
The result is then a photonic version of the interaction between electricity and magnetism, in this case with a concentration of photons in discrete bands of energy, providing a tool to increase the interaction of light with matter and many other applications.
“When you have flat bands [de energia], this means that the light stays in the same place longer, which means that whatever you are trying to do with the light, you can do more efficiently. We are currently investigating whether we can use this design for more efficient lasers in photonic chips,” said Rechtsman.
Photon crystal from the Dutch team.
[Imagem: Ren Barczyk et al. – 10.1038/s41566-024-01412-3]
Making the light stop
The Dutch team also built their own photonic crystal, but with a slightly different geometry, trying to imitate the behavior of electrons in graphene.
The result obtained accentuates the strange “freezing of light” behavior: at Landau levels, the light waves no longer move, they no longer flow through the crystal, they remain stationary. The researchers were able to demonstrate this, showing that the deformation of the crystal array has a similar effect on photons as the magnetic field does on electrons.
“By playing with the deformation pattern, we were even able to establish various types of effective magnetic fields in a material. As a result, photons can pass through certain parts of the material but not others. Consequently, these insights also provide new ways to direct light on a chip,” said Professor Ewold Verhagen.
Article: Direct observation of Landau levels in silicon photonic crystals
Authors: Maria Barsukova, Fabien Gris, Zeyu Zhang, Sachin Vaidya, Jonathan Guglielmon, Michael I. Weinstein, Li He, Bo Zhen, Randall McEntaffer, Mikael C. Rechtsman
Magazine: Nature Photonics
DOI: 10.1038/s41566-024-01425-y
Article: Observation of Landau levels and chiral edge states in photonic crystals through pseudomagnetic fields induced by synthetic strain
Authors: Ren Barczyk, L. Kuipers, Ewold Verhagen
Magazine: Nature Photonics
DOI: 10.1038/s41566-024-01412-3
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