In 1972, physicists J. Michael Kosterlitz and David Thouless published a groundbreaking theory of how phase changes could occur in two-dimensional materials. Experiments soon showed that the theory correctly captured the process of a helium film transitioning from a superfluid to a normal fluid, helping to usher in a new era of research on ultra-thin materials, not to mention earning Kosterlitz, a professor at Brown University, and Thouless shares of the 2016 Nobel Prize in Physics.
But the Kosterlitz-Thouless (K-T) theory aimed to explain more than the superfluid transition. The pair also hoped it might explain how a two-dimensional solid could melt into a liquid, but experiments so far have failed to clearly validate the theory in that case. Now, new research by another group of Brown physicists could help explain the mismatch between theory and experiment.
The research, published in Proceedings of the National Academy of Sciences, shows how impurities — “extra” atoms in the crystalline structure of a material — can disrupt the order of a system and cause melting to begin before the K-T theory
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Image: Researchers used tiny beads arranged in a crystalline lattice to investigate how two-dimensional solids melt. CREDIT: Brown University