“Ultimate-density atomic semiconductor via flat phonon bands”
Dispersion-less flat energy bands in momentum space are known to generate extremely localized states in real space. We discovered that flat phonon bands exist surprisingly in the commercial ferroelectric HfO2 and produce a localized motion of atoms as if their chemical bond temporarily disappears by an external voltage. With the vanishing bond, each atom can be freely displaced by the voltage for the information storage. Our discovery of the atom control directly in a solid will lead us to the design of ultimate-density memory semiconductors reaching up to ~100 TB . Our theory is directly applicable to the Si-compatible HfO2 so can be materialized in all electronic devices . Just as Einstein’s theory of relativity (E=mc2) enabled us to make bombs out of atoms not out of materials, with our “Atomic Semiconductor” we will open the era of designing memories on an atomic scale rather than a materials scale and carrying a data center in the palm of your hand.
 “Scale-free ferroelectricity driven by flat phonon bands in HfO2”, H.-J. Lee et al., Science 369, 1343 (2020).
 “A key piece of the ferroelectric hafnia”, B. Noheda et al., Science 369, 1300 (2020).
Dr. Jun Hee Lee is a computational materials scientist. He obtained his PhD in physics from Seoul National University in 2008. Then he moved to USA as a postdoc at Physics Dept. of Rutgers U (2008~2011), Chemistry Dept. of Princeton U (2011~2013), and Materials division of Oak Ridge National Lab. (2013~2015). Now he joined UNIST in Korea in 2015 as an assistant professor and is an associate professor. Combining his interdisciplinary background, he has been actively working on various fields such as ferroelectrics, multiferroics, polymers, and energy materials including photocatalysts, fuel cells, and batteries. He published 70 SCI papers including a recent theory paper in Science “Scale-free ferroelectricity by flat phonon bands in HfO2”, Science 369, 1343 (2022). Nowadays he is extending his theoretical research across industries to realize ultimate-density semiconductors reaching up to ~100 TB.