There has been a fabulous new achievement in particle physics.
For the first time, scientists have been able to imagine the orbits of electrons within a quasiparticle known as an exciton, a result that has finally allowed them to measure the excitonic wave function by describing the spatial distribution of the moment of electrons within the quasiparticle.
This success has been sought since the discovery of excitons in the 1930s and, although at first it may seem abstract, it can aid in the development of various technologies, including applications of quantum technology.
“Excitons are really unique and interesting particles; they are electrically neutral, which means they behave very differently within the materials of other particles such as electrons. Their presence can change the way a material responds to light. said physicist Michael Man of the Okinawa Institute. Science and Technology (OIST) Femtosegon Spectroscopy Unit in Japan.
“This work brings us closer to fully understanding the nature of excitons.”
The electronic probability distribution of an exciton shows where the electron is most likely to be found. (OIST)
An excitation is not a true particle, but a quasiparticle, a phenomenon that arises when the collective behavior of particles causes them to act similarly to particles. Semiconductors give rise to excitons, more conductive materials than an insulator, but not enough to be considered suitable conductors.
Semiconductors are useful in electronics as they allow a greater degree of control over the flow of electrons. Although difficult to observe, excitons play an important role in these materials.
Excitons can form when the semiconductor absorbs a photon (a particle of light) that elevates negatively charged electrons to a higher energy level; that is, the photon “excites” the electron, leaving a positively charged vacuum called an electron hole. The negative electron and its positive hole join in a mutual orbit; an exciton is that pair of electron-electron holes it orbits.
But excitons have a very short life and are very fragile, as the electron and its hole can come back together in just a fraction of a second, so we won’t actually see them.
“Scientists first discovered excitons about 90 years ago,” said physicist Keshav Dani of the OIST’s Femtosecond Spectroscopy Unit.
“But until very recently, it was generally possible to access only the optical signatures of excitons, for example, the light emitted by an exciton when it is extinguished. Other aspects of its nature, such as its momentum, and how they orbit the electron and the hole each other, they could only be described theoretically “.
This is a problem that researchers have been working to solve. In December last year, they published a method for directly observing the timing of electrons. They have now used this method. And it worked.
The technique uses a two-dimensional semiconductor material called tungsten diselenide, housed in a vacuum chamber that cools to a temperature of 90 Kelvin (-183.15 degrees Celsius or -297.67 degrees Fahrenheit). This temperature must be maintained to prevent the excitons from overheating.
A laser pulse creates excitons in this material; a second ultra-high energy laser completely expels the electrons into the vacuum of the vacuum chamber, which is controlled by an electron microscope.
This instrument measures the velocities and trajectories of electrons, information that can be used to work the initial orbits of particles at the point where they were ejected from their excitons.
Square wave function of an exciter. (Man et al., Sci. Adv., 2021)
“The technique has some similarities to high-energy physics colliding experiments, where particles break together with intense amounts of energy, breaking them open. Measuring the trajectories of the smallest internal particles produced in the coll. “Scientists can begin to tear together the internal structure of the original intact particles,” Dani explained.
“Here we are doing something similar: we use photons of extreme ultraviolet light to break excitons and measure the trajectories of electrons to imagine what is inside.”
Although it was a delicate and time-consuming job, the team was finally able to measure the wave function of an exciter, which describes its quantum state. This description includes its orbit with the electron hole, which allows physicists to accurately predict the position of the electron.
With a few modifications, the team’s research could be a big leap forward for exciton research. It could be used to measure the wave function of different exciton states and configurations, and to probe the excitation physics of different materials and semiconductor systems.
“This work represents a major breakthrough in the field,” said physicist Julien Madeo of the OIST Femtosegon Spectroscopy Unit.
“Being able to visualize the internal orbits of particles as they form larger composite particles could allow us to understand, measure, and ultimately control composite particles in unprecedented ways. This could allow us to create new quantum states of matter and technology. based on these concepts. “
The team’s research has been published in Scientific advances.