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Credit: CC0 Public Domain
Excitons, electrically neutral quasiparticles, have extraordinary properties. They exist only in semiconductor and insulating materials and are easily accessible in two-dimensional (2D) materials of a few atoms of thickness, such as carbon and molybdenite. When these 2D materials are combined, they exhibit quantum properties that none of them own by itself.
A new study from Tel Aviv University explores the generation and propagation of excitons in 2D materials in a short and unprecedented time frame and with extremely high spatial resolution. The research was conducted by Professors Haim Suchowski and Michael Mrejen of the Faculty of Exact Sciences Raymond & Beverly Sackler of TAU and published in Progress of science February 1st.
Quantum mechanics is a fundamental theory in physics that describes nature at the smallest scales of energy. "Our new imaging technology captures exciton movement in a short time and at the nanoscale," says Dr. Mrejen. "This tool can be extremely useful for taking a look at the response of a material from the first moments when the light has affected it."
"Such materials can be used to dramatically slow down the light to manipulate or even store it, much needed for communications and quantum-based quantum computers," said Professor Suchowski. "From the point of view of instrument capabilities, this tour de force opens up new possibilities for visualizing and manipulating the ultra-fast response of many other material systems in other spectral regimes, such as the average infrared range in which many molecules vibrate. "
Scientists have developed a unique space-time imaging technique at the nanoscale and femtosecond scales and observed the exciton-polariton dynamics in tungsten diselenide, a semiconductor material at room temperature.
The exciton-polariton is a quantum creature created by the coupling of light and matter. Due to the specific material studied, the measured velocity of propagation was about 1% of the speed of light. At this time scale, the light travels only a few hundred nanometers.
"We knew we had a unique characterization tool and that these 2D materials were good candidates for exploring interesting behavior at the ultra-fast-ultra intersection," says Dr. Mrejen. "I must add that the material, tungsten diselenide, is extremely interesting from the point of view of applications.He maintains such coupled light-matter states in very small dimensions, up to the thickness of an atom, at the ambient temperature and in the visible spectral range. "
Researchers are currently studying ways to control the speed of semiconductor waves, for example by combining several 2D materials in stacks.
Explore further:
Excitons pave the way for more efficient electronics
More information:
M. Mrejen et al, exciton-polariton transient dynamics in WSe2 by near-field high-speed imaging, Progress of science (2019). DOI: 10.1126 / sciadv.aat9618
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