Quasiparticles Found to Have a Critical Role in Future Applications for Quantum Computing and Memory Storage

June 23, 2020 by Gary Elinoff

Discerning the properties of tiny quasiparticles is a significant step toward developing new types of electronic components.

Researchers at Rensselaer Polytechnic Institute (RPI) have announced their discovery of intriguing new facts about a type of quasiparticle known as an exciton. The group's work serves to grasp the potential of transitional metal dichalcogenides (TMDCs). These atomically thin class of materials have attracted attention due to their electronic and optical properties. 

The results of the work, published in Nature Communications, focused on TMDCs, with an emphasis on the exciton, which is often produced through the energy of light and result when a negatively charged electron bonding with a hole particle carrying a positive charge.

The research team (headed by Rensselaer's Sufei Shi, an assistant professor of chemical and biological engineering), found that the interaction between electrons and holes within this atomically thin semiconductor material can be quite powerful. So much so that the electron and hole within the exciton can bond with a third particle, either an electron or a hole, to form a trion. 

In the present study, Shi and his team succeeded in manipulating the TMDC material in a manner to cause the internal crystalline lattice to vibrate. This, in turn, served to create a phonon, which is another type of quasiparticle. The phonon was observed to interact strongly with a trion. 

What is a Phonon?

All solid crystals are built of atoms bound in repeatable three-dimensional lattices. The atoms themselves can be thought of as particles connected by springs. Phonons can be described as units of vibrational energy engendered by the atoms' oscillation within the crystalline structure.

The vibration generates mechanical waves that propagate through the material with specific momentum and energy. In terms of quantum mechanics, these waves can be treated as a particle, and that particle is our photon. 

Just as a photon is a quantum of light or electromagnetic energy, the phonon is a quantum of mechanical, specifically vibrational energy.


Illustration of an exciton.

An illustration of the formation of exciton. Image credited to Rensselaer.


Determining Effective Mass

The researchers placed the material within a powerful magnetic field. This allowed them to analyze the light emitted from the TMDCs from the phonon interaction, thus determining the effective mass of the electron and hole individually.

The result was surprising. The investigators have assumed that there would be symmetry in mass, but as described by Shi, the team found that the measurement was "significantly different."


Developing a Practical Electronic or Optoelectronic Device

As described by Professor Shi, knowledge of effective mass is a significant step forward. "We have developed a lot of knowledge about TMDCs now," Shi said. "But to design an electronic or optoelectronic device, it is essential to know the effective mass of the electrons and holes. This work is one solid step toward that goal." 


There is today an acceleration of building things smaller, lighter, and ever more energy efficient. While Professor Shi's work at Rensselaer may not lead to off the shelf components in the near term, they point in a direction. 

The direction is unmistakable.

We recently reported using photonics to transfer information internally and between chips and how quantum-mechanical spins are being used to convey information. Moore's Law may or may not have been overturned, but it may be losing its relevance. Its the heat generated by moving electrons that is rapidly becoming the limiting factor in electrical engineering, maybe even more so than the number of bits that can be held in a device of a given physical size.

For this reason, the various forms of quantum computing, not reliant on wandering electrons and their cost in power and heat, may well define our industry's future.