After nearly a century of exploring the nature of tiny ephemeral objects called excitons, researchers have finally succeeded in visualizing the structure, insinuating the true location of an electron. The findings could eventually help physicists create new states of matter or new quantum technologies.
Excitons occur in semiconductors and other materials such as insulators. When a semiconductor absorbs photons, or particles of light, it causes electrons to jump to higher energy levels, leaving positively charged holes in their place. The electrons and the holes orbit each other, forming an excitation – basically the whole mode of an electron and the hole. Because the selection has a negative charge and the hole a positive charge, the excitation itself is neutral. The excitons are momentary, as the electrons almost always click immediately back into their holes. When the electrons fall back, they emit a photon.
“Scientists first discovered excitons about 90 years ago,” said co-author Keshav Dani, the head of the Femtosecond Spectroscopy Unit at the Okinawa Institute of Science and Technology, at a university. press release. “But until very recently one could generally access only the optical signatures of excitons – for example, the light emitted by excitation when extinguished. Other aspects of their nature, such as their momentum, and how the electron and the hole orbit each other, could only be theoretically described. “
Because electrons function as both particles and waves, their location and momentum cannot be specified at the same time. The “probable cloud” of excitation – the sphere of influence it makes up – is the best indicator where the electron can lie around the hole.
The researchers tried to map the wave functions of the excitons, which would directly define the shape and size of the structure. The work comes after the last years explored of the same team, which described a method for detecting excitatory momentum. For the current job, published today in the journal Science Advances, the team fired laser light at a semiconductor, catalyzing the absorption of photons. The semiconductor was extremely slender – a two-dimensional oblate of matter only a few atoms thick.
When the excitation formed, the team then separated them with high-energy photons, blowing up the electrons. They used an electron microscope to map the output of the electrons.
“The technique has some similarities to the collision experiments of high-energy physics, where particles are shattered along with intense amounts of energy, breaking them down,” Dani said. “Here we’re doing something similar – we’re using extreme ultraviolet light photons to separate excitons and measure the trajectories of the electrons to visualize what’s inside.”
By measuring how the electrons left the semiconductor, the researchers could put together the locations, shapes, and sizes of the excitons. The image above of this article looks a bit like the Sun on a clear sky, but it shows the probable cloud of excitement; in other words, the spaces where the electron most likely flies around the hole it left behind.
“This work is a major breakthrough in the field,” said lead author Julien Madeo, a hired scientist in the OIST Femtosecond Spectroscopy Unit, in the OIST edition. “Being able to visualize the internal orbits of particles as they form larger composite particles could allow us to understand, measure and ultimately control the composite particles in unprecedented ways. This could allow us to create new quantum states of matter and technology based on these concepts. “
What is to you a target view on a honeycomb background and a boon for scientists eager to learn more about the quantum physics played in semiconductors, possibly improving the projects of such technologies in the future. Now almost a century from the first prediction of the excitation in 1931, we are closer to imagining how the subatomic structure actually manifests. The observations have yet to take place in very cold states, although that temperature has risen a few years ago. The newly described excitations lead us to a more complete understanding of these quantum mechanics – and more developments will certainly unfold as the excitement reaches its centennial century.
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