Technion observes light-sound waves in 2D materials, first time in history

The scientists sent pulses of light around the edges of these 2D materials using a ultrafast transmission electron microscope (UTEM), which produced within it hybrid sound-light waves.

By JERUSALEM POST STAFF
Technion's experimental setup. The quantum microscope (photo credit: NITZAN ZOHAR/TECHNION SPOKESPERSON'S OFFICE)
Technion's experimental setup. The quantum microscope
(photo credit: NITZAN ZOHAR/TECHNION SPOKESPERSON'S OFFICE)
Researchers from the Technion Israel Institute of Technology in Haifa have recorded the transmission of combined sound and light waves in atomically thin materials.
"Single-layer materials, alternatively known as 2D materials, are in themselves novel materials, solids consisting of a single layer of atoms," Technion explained in a statement. "Graphene, the first 2D material discovered, was isolated for the first time in 2004, an achievement that garnered the 2010 Nobel Prize."
Using these materials, Technion showed for the first time in history how pulses of light move through these materials, which they published in the scientific journal Science after their discoveries garnered high-levels of interest from members of the scientific community.
"Light moves through space at 300,000 km/s. Moving through water or through glass, it slows down by a fraction," Technion said. "But when moving through certain few-layers solids, light slows down almost a thousand-fold. This occurs because the light makes the atoms of these special materials vibrate to create sound waves (also called phonons), and these atomic sound waves create light when they vibrate.
"Thus, the pulse is actually a tightly bound combination of sound and light, called 'phonon-polariton.' Lit up, the material 'sings.'"
To arrive at their findings, the scientists sent pulses of light around the edges of these 2D materials using a ultrafast transmission electron microscope (UTEM), which produced within it hybrid sound-light waves.
Within the discovery, Technion noted that not only could the researchers record the lightwaves but also noticed they could be sped up and slowed down, and at one point the pulses could even split separately at different speeds.
The UTEM microscope allows particles to pass through the sample, which is then received by a detector. This process gives the researchers the ability to track the sound-light wave in "unprecedented revolution," Technion said, through space and time. The time resolution is equal to the number of seconds in a million years.
“The hybrid wave moves inside the material, so you cannot observe it using a regular optical microscope,” said Robert and Ruth Magid Electron Beam Quantum Dynamics Laboratory head Professor Ido Kaminer's graduate student Yaniv Kurman. “Most measurements of light in 2D materials are based on microscopy techniques that use needle-like objects that scan over the surface point-by-point, but every such needle-contact disturb the movement of the wave we try to image.

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"In contrast, our new technique can image the motion of light without disturbing it," Kurman added. "Our results could not have been achieved using existing methods. So, in addition to our scientific findings, we present a previously unseen measurement technique that will be relevant to many more scientific discoveries.”
Kurman was responsible for completing the mathematical equations to predict how light "should" behave as it passes through 2D materials and how it can be measured, during the COVID-19 pandemic when the universities were closed.
His colleague, graduate student Raphael Dahan, worked towards realizing how to focus infrared pulses into the UTEM, and completed upgrades on the machine to allow for it to arrive at the necessary conclusions. When classes resumed at universities around the country, the team was able to prove Kurman's theory and even observe "additional phenomena that they had not expected," Technion said.
“We can use the system to study different physical phenomena that are not otherwise accessible,” said Prof. Kaminer. “We are planning experiments that will measure vortices of light, experiments in Chaos Theory, and simulations of phenomena that occur near black holes.
"Moreover, our findings may permit the production of atomically thin fiber optic “cables”, which could be placed within electrical circuits and transmit data without overheating the system – a task that is currently facing considerable challenges due to circuit minimization.”
Other examples of its application could broaden the capabilities of electron microscopes and promote the possibility of optical communication through atomically thin layers.
“I was thrilled by these findings,” said Professor Harald Giessen of the University of Stuttgart, who did not participate in the research. “This presents a real breakthrough in ultrafast nano-optics, and represents state of the art and the leading edge of the scientific frontier.
"The observation in real space and in real time is beautiful and has, to my knowledge, not been demonstrated before.”


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