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Exploring Extreme Quantum Matter: Sodium at 500 GPa

Danae N Polsin

Monday, November 9, 2020

At high-energy-density (HED) conditions, a new realm of quantum behavior emerges where the extreme compression of matter leads to electron localization, structural complexity, and core electron chemistry. High-pressure can significantly modify the electronic structure of matter, and sodium is the ideal material to explore such behavior. At 200 GPa, Na transforms from a simple free-electron metal to a structurally-complex transparent insulator. This transparent phase is expected to be an electride, where electrons are localized in interstitial positions due to the density-driven quantum mechanical constraints on the electronic wavefunctions. We report the structural and electronic properties of Na in an unexplored regime, where the interatomic spacing approaches the Na+ ionic radius.  Using lasers as a high-pressure driver, x-ray diffraction measurements up to 480 GPa and 2000 K reveal peaks unaccounted for by the hP4 electride phase that is predicted to be stable to 1.75 TPa.  In striking contrast to static compression studies, the phase is not transparent, but a significant decrease in the conductivity suggests an opening of the electronic band gap.  These reflectivity measurements, corroborated with DFT calculations, are consistent with a high-temperature electride phase.

This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.