Physics professor Peter Abbamonte and graduate students Anshul Kogar and Mindy Rak, in collaboration with colleagues from Illinois, the University of California, Berkeley and the University of Amsterdam, have demonstrated the existence of a new form of matter, which has stumped the scientific community and was first theorized nearly 50 years ago. It’s about excitonium.
Excitonium is composed of excitons (particles that are formed by an electron and a hole, linked through the coulombian interaction), a type of boson; a composite particle that could allow matter to act as a superfluid, a superconductor, or even an insulating electronic crystal.
It had never been detected before, but in the 1960s, it was the Harvard theoretical physicist Bert Halperin who theorized and coined the term for the first time in history.
Excitonium is a condensate made up of excitons, which means the researchers detected that it was a solid. This peculiar quantum-mechanical pairing of electrons and the holes they left behind is possible because, in semiconductors, electrons at the edge of one energy level in an atom can, when excited, jump to the next energy level, leaving behind a ” hole “on the previous level.
This hole acts like a positively charged particle, attracting the escaped negatively charged electron. Thus, they orbit each other in the same way as an electron and a proton.
Proving its existence
To demonstrate the existence of excitons, the scientists studied the undoped crystals of transition metal titanium dicalcogenide diselenide (1T-TiSe2) and reproduced the results five times on different cleaved crystals, separately.
During previous attempts it had not been possible to distinguish between exciton formation and superficially similar processes. To carry out the new experiment, the physicists developed a new spectroscopic technology, much more sensitive to charged particles.
Specifically, the scientists made the first observation of a soft plasmon, which arose when the material approached its critical temperature of 190º Kelvin. This phase represents a key evidence of exciton condensation into a three-dimensional solid and the first definitive evidence for the discovery of excitonium, the authors explain.
“This result is of cosmic significance,” Abbamonte stated in a press release.
“Ever since the term ‘excitonium’ was coined in the 1960s by Harvard University theoretical physicist Bert Halperin, physicists have tried to prove its existence. Theorists have debated whether it would be an insulator, a perfect conductor, or a superfluid. , with some convincing arguments all over the place, “he continues.
Now that its existence has been proven and has been specifically observed in experimentation, its properties can be explored and its potential applications assessed.
Most obviously, this material, as a superconductor and superfluid, could be used to promote existing technologies . Furthermore, since the analysis of quantum phenomena is what guides and shapes our understanding of quantum mechanics, this research could help to further demystify current quantum puzzles.
Referencia: Anshul Kogar, Melinda S. Rak, Sean Vig, Ali A. Husain, Felix Flicker, Young Il Joe, Luc Venema, Greg J. MacDougall, Tai C. Chiang, Eduardo Fradkin, Jasper van Wezel, Peter Abbamonte. Signatures of exciton condensation in a transition metal dichalcogenide. Science, 2017; 358 (6368): 1314 DOI: 10.1126/science.aam6432
