Researchers have achieved something that has been dreamt for a century: creating the first image of the spatial distribution of an electron inside an exciton. This achievement is reported in the journal Science Advances.
The exciton is a quasi-particle – it acts like a particle, but is not really a particle. They are fundamental in semiconductor technology such as LEDs and smartphones. They form easily – an electron is freed from its atom within the semiconductor thanks to an energetic photon, a particle of light. The electron is negatively charged, and by being removed leaves behind a positively charged hole.
The electron doesn’t always fall back into the hole, sometimes starting to orbit it, thus creating an exciton. In quantum mechanics, it is impossible to know the position and momentum of a particle with arbitrary precision. The best that can be done is to look at the probability distribution, and this is what we are seeing in the image: Where an electron is likely to be found within the exciton.
"Excitons are really unique and interesting particles; they are electrically neutral which means they behave very differently within materials from other particles like electrons. Their presence can really change the way a material responds to light," Dr. Michael Man, co-first author and staff scientist in the OIST Femtosecond Spectroscopy Unit, said in a statement. "This work draws us closer to fully understanding the nature of excitons."
Despite their importance in semiconductors, these quasiparticles are extremely fragile when it comes to studying them. It is very easy to break them apart, and in certain materials, they only last for a minuscule fraction of a second. The technique that allowed the team to study these excitons in more detail was only announced a few months ago, and this is an excellent follow-up result.
"Scientists first discovered excitons around 90 years ago," said Professor Keshav Dani, senior author and head of the Femtosecond Spectroscopy Unit at OIST. "But up until very recently, one could generally access only the optical signatures of excitons - for example, the light emitted by an exciton when extinguished. Other aspects of their nature, such as their momentum, and how the electron and the hole orbit each other, could only be described theoretically."
The work not only gives a better understanding of the exciton, but it might lead to having the ability to actually control these quasiparticles and improve the technologies in which they are employed in the future.
2
