Yale-NUS Associate Professor of Science (Physics) Shaffique Adam is the lead author for a recent work that describes a model for electron interaction in Dirac materials, a class of materials that includes graphene and topological insulators, solving a 65-year-old open theoretical problem in the process. The discovery will help scientists better understand electron interaction in new materials, paving the way for developing advanced electronics such as faster processors. The work was published in the peer-reviewed academic journal Science on 10 August 2018.
Electron behaviour is governed by two major theories -- the Coulomb's law and the Fermi liquid theory. According to Fermi liquid theory, electrons in a conductive material behave like a liquid -- their "flow" through a material is what causes electricity. For Dirac fermions, the Fermi liquid theory breaks down if the Coulomb force between the electrons crosses a certain threshold: the electrons "freeze" into a more rigid pattern which inhibits the "flow" of electrons, causing the material to become non-conductive.
For more than 65 years, this problem was relegated to a mathematical curiosity, because Dirac materials where the Coulomb threshold was reached had never been made. Today, however, we routinely make use of quantum materials for applications in technology, such as transistors in processors, where the electrons are engineered to have desired properties, including those which push the Coulomb force past this threshold. But the effects of strong electron-electron interaction can only be seen in very clean samples.
In the work immediately following his PhD, Assoc Prof Adam proposed a model to describe experimentally available Dirac materials that were "very dirty" (contains a lot of impurities). However, in the years that followed, newer and cleaner materials have been made, and this previous theory no longer worked.
In this latest work titled, "The role of electron-electron interactions in two-dimensional Dirac fermions," Assoc Prof Adam and his research team have developed a model which explains electron interactions past the Coulomb threshold in all Dirac materials by using a combination of numerical and analytical techniques.
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