Electronic properties of condensed matter are often determined by an intricate competition between kinetic energy that aims to overlap and delocalize electronic wave functions across the crystal lattice, and localizing electron-electron interactions. In contrast, the gaseous phase is characterized by valence electrons tightly localized around the ionic atom cores in discrete quantum states with well-defined energies. As an exotic hybrid of both situations, one may wonder which state of matter is created when a gas of isolated atoms is suddenly excited to a state where electronic wave functions spatially overlap, like in a solid?
Source:
https://phys.org/news/2020-06-metal-like-quantum-gas-pathbreaking-platform.html