Jun Hee Lee, Ulsan National Institute of Science and Technology (UNIST)

"Ultimate-density atomic semiconductor via flat phonon bands"

Abstract: Dispersion-less flat energy bands in momentum space generate localized states and cause unconventional phenomena such as graphene superconductivity in electrons and individual spin flips in magnons. However flat bands in phonon were not discovered yet. For the first time, we discovered flat bands in phonon exist surprisingly in a 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 [1]. Our theory is directly applicable to the Si-compatible HfO₂ so can be materialized in all electronic devices [2]. 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.

[1] “Scale-free ferroelectricity driven by flat phonon bands in HfO₂”, H.-J. Lee et al., Science 369, 1343 (2020).[2] “A key piece of the ferroelectric hafnia”, B. Noheda et al., Science 369, 1300 (2020).