Physicists from Professor Alexander Szameit’s group (University of Rostock), in collaboration with Professor Mordechai Segev’s group (Technion, Israel Institute of Technology), have demonstrated a new type of mechanism that can prevent the free propagation of light waves. Until now, the underlying physical effect was considered too weak to completely stop the wave expansion. In their recent experiments, physicists have observed that such localization of light is still possible, as evidenced by the mysterious sensitivity of wave propagation over a wide range of spatial length scales. Their discovery was recently published in a magazine Scientific advances.
In 1958, Phil Anderson surprised the international scientific community by predicting that an electrical conductor (such as copper) could suddenly turn into an insulator (such as glass) when the order of atomic crystals was sufficiently shaken. In physicists’ jargon, such a “disorder” can pin otherwise free-moving electrons down, thus preventing any substantial electric current through the material. This physical phenomenon, known as “Anderson localization,” can only be explained by modern quantum mechanics, where electrons are treated not only as particles but also as waves. As it turns out, this effect, for which Phil Anderson won the 1977 Nobel Prize in Physics, also applies to classical environments: The disorder can also suppress the propagation of sound waves or even light rays.
The research of physics professors Alexander Szameit and Mordechai Segev deals with the properties of light and its interaction with matter. Recently, Professor Segev’s team made a stunning discovery: Light waves may even show Anderson’s location if the fault is practically on them. This new type of perturbation, which goes far beyond Phil Anderson’s original considerations, contains exclusively spatially periodic distributions with certain wavelengths.
“It would be naively expected that only those waves whose spatial distribution somehow matches the fault’s length scales can be affected and potentially experience Anderson’s localization,” explains Sebastian Weidemann, a Ph.D. student of the Institute of Physics in the group of Professor Szameit.
“The other waves should basically propagate as if there was no disturbance at all,” continues Dr. Mark Kremer, who is also from Professor Szameit’s group.
In contrast, Technion’s recent theoretical work has suggested that wave propagation can be dramatically affected by such an “invisible disorder.”
“When light waves can interact with an invisible disorder multiple times, a surprisingly strong effect can be created and stop all light propagation,” says Ph.D. student Alex Dikopoltsev from Professor Segev’s group as describing the effect.
For the first time, physicists from Rostock and Israel are working closely together to demonstrate a new localization mechanism. “To this end, we’ve designed man-made unmounted materials from miles of optical fibers. Our complex-arranged optical networks mimic the spatial propagation of electrons in unordered materials. This has allowed us to directly observe how virtually invisible structures can successfully capture light waves.” Explains Sebastian Weidemann, who performed the experiments together with Dr. Mark Kremer.
These discoveries represent a significant advance in basic research on wave propagation in disordered media and potentially pave the way for a new generation of synthetic materials that use the disorder to selectively suppress currents; whether light, sound or even electrons.
Stop-motion photons: Localized light particles on the road
Alex Dikopoltsev et al, Observation of Anderson localization outside the spectrum of the disorder, Scientific advances (2022). DOI: 10.1126 / sciadv.abn7769
Provided by the University of Rostock
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