The journal Science reports on an unprecedented experimental observation made by researchers at the Technion - real-time tracking of the movement of a combined light-sound wave moving through a material with a thickness of individual atoms. The researchers were able to follow the movement of the wave from its formation to its final decay
The journal Science reports a first success inMapping the movement of light in a XNUMXD material in real time. Using an electron microscope, researchers at the Technion followed the movement of integrated wave - A sound wave and a light wave moving in this material as one piece. This success is not only a scientific achievement but also an opening to many practical breakthroughs because short pulses are the building block of optical communication and information transmission in the modern world.
The research was led ד"R. Edu Kaminer, head of the Laboratory for Quantum Dynamics of Electron Beams p"Q. Robert and Ruth Magid, and the doctoral student Yaniv Korman from the Faculty of Electrical and Computer Engineering p"Q. Andrew and Erna Viterbi at the Technion. Dr. Kaminer is also a member of the Russell Berry Nanotechnology Institute (RBNI) and the Helen Diller Quantum Center. Raphael Dahan, Dr. Kangfeng Wang, Michael Yanai, Yuval Adib and Uri Reinhardt from Dr. Kaminer's AdQuanta laboratory and researchers from universities in the United States, Spain and France also participated in the study.
Two-dimensional materials, i.e. structures with a thickness of a single atom, are a new discovery and a relatively young field of research; It was only in 2004 that such a material was developed for the first time by the physicists Andre Geim and Konstantin Novoslov, later winners of the Nobel Prize in Physics (2010). Using simple adhesive paper, the two peeled off thin layers from a block of graphite until they reached a thin layer known today as "graphene". They showed that the properties of this layer - conductivity, strength, etc. - are very different from the properties of the graphite block in terms of strength and electrical conductivity.
Over the years, their properties have also become clearOptical The uniqueness of graphene and of different two-dimensional materials. It turns out that light waves at certain frequencies vibrate the atoms of the two-dimensional material in such a way that a sound wave affects the light wave. The Technion researchers created a combined "light-sound" wave in the material that moves as one piece. This is of course counterintuitive, since the speed of light we all know (about 300 million meters per second) is almost a million times higher than the speed of sound (about 340 meters per second). The explanation is the data question when it comes to movement in the free air, however The two-dimensional material slows down light and speeds up sound And so the joint movement of the two types of wave is possible.
integrated wave
The existence of the wave integrated in the material was already known, but so far the pattern of its progression has not been deciphered. Now, as mentioned, the Technion researchers were able to map the movement of the integrated wave in the two-dimensional material and track its movement from its formation to its final decay.
The Technion researchers sent laser bursts (pulses) to the edges of the model (the two-dimensional structure) that created the hybrid waves in the material. The researchers discovered that these waves travel at a speed almost 1,000 times slower than the speed of light in free air (and almost 1,000 times faster than the speed of sound in free air).
But that wasn't the only surprise. According to Dr. Kaminer, "We discovered that the integrated wave changes its speed in the material spontaneously - it speeds up and slows down." Another surprise is that the wave splits into two different pulses moving at different speeds." The result demonstrated in the attached photo and video is the product of billions of such measurements.
The entire experiment was conducted using an ultrafast transmission electron microscope (ultrafast TEM). This microscope makes it possible to follow the integrated wave with an unprecedented resolution of time and space. Unlike an optical microscope which is limited to the diffraction limit, in a penetrating electron microscope the electrons pass way The model and can reach atomic spatial resolution. The time resolution is made possible with the help of a pulsed laser that excites both what you want to measure in the model but also the electrons being measured. To explain the ear, it is 50 femtoseconds, that is 50X10-15 of a second (the number of frames per second is equal to the number of seconds in a million years).
According to Korman, "You have to understand that the integrated wave, or the pulse, moves right inside the two-dimensional material and therefore it is impossible to look at it from the outside using a normal optical microscope. Almost all measurements of light in atomic materials are made by a microscopy method that touches the material, but any such contact interferes with the motion of the wave. Our findings cannot be obtained with the existing methods, therefore, beyond the current scientific discovery, we present here A measurement method that has never been seen in this field of research And will be relevant to many more discoveries."
The construction of the experimental setup was a huge technological challenge, and another achievement in the current research is the launch of an infrared frequency laser pulse inside the two-dimensional material in the electron microscope. Corman and Dr. Kaminer emphasize that this success was achieved thanks to doctoral student Raphael Dahan, who was the laboratory engineer at the time of the experiment. The improvements that Dahan introduced in the system made it possible to send pulses of light to the model that generated the hybrid wave and at the same time to cause the microscope to map the movement of the waves.
Although it is pure science, the researchers estimate that it will have research and other applications. According to Dr. Kaminer, "In the first step we will be able to use the system to study various physical phenomena that are not accessible in any other way. We are planning experiments related to the measurement of vortices of light, experiments in chaos theory and even attempts to design new quantum computing units. From an engineering point of view, our findings may allow the production of atomically thick optical fibers, which will be placed right inside electrical circuits and thus transmit information without heating the circuit - a task that currently faces many challenges due to the miniaturization of electronic and other devices."
Surprising findings
The study was based on a new collaboration with leading research groups in the United States (Prof. James Edgar, Kansas State University), France (Prof. Mathieu Kosiak, Université Paris-Saclay), and Spain (Prof. Frank Coppens and the postdoctoral fellow Dr. Hanan Herzig Shinefox, ICREA, ICFO).
It arouses enormous interest in the scientific community, as is evident both in the acceptance of the article to the prestigious journal Science and in the reviews that led to its acceptance. "The findings surprised me," said Prof. Harald Giessen from the University of Stuttgart, who was not involved in the research. "This is a real breakthrough in ultrafast nanooptics, achieved thanks to innovative and pioneering scientific work. The observation in real space and in real time is, as far as I know, unprecedented."
Physicist Prof. John Joanopoulos from MIT commented on the research and said that "the work of Ado Kaminer, his group members and colleagues is an important step towards research and understanding of the dynamic properties of an integrated wave. Such waves, for example the wave packets in two-dimensional materials, are fascinating both scientifically and technologically. The research being published now allows for the first time a direct experimental observation of the time-space properties of these waves in two-dimensional materials, and this is of enormous importance to the field."
ד"R. Ado Kaminer He won the Blavatnik Award for 2021 for young researchers in the category of physical sciences and engineering, and was recently accepted into the Israeli Young Academy.
Yaniv Korman, 31 years old, began studying at the Technion in 2012 for a double bachelor's degree in electrical engineering and physics and from there continued to a master's degree and a doctorate in a direct track under the guidance of Dr. Ado Kaminer at the Viterbi Faculty of Electrical and Computer Engineering.
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Does this mean that when will we learn to control the speed of light? Or did I not understand anything?
Well done