title: Dynamical crossover at the liquid-liquid transformation of a compressed molten alkali metal.
abstract: Density-driven phase transformations are a known phenomenon in liquids. Pressure-driven transitions from an open low-density to a higher-density close-packed structure were observed for a number of systems. Here, we show a less intuitive, inverse behavior. We investigated the electronic, atomic, and dynamic structures of liquid Rb along an isothermal line at 573 K, at 1.2-27.4 GPa, by means of ab initio molecular dynamics simulations and inelastic x-ray scattering experiments. The excellent agreement of the simulations with experimental data performed up to 6.6 GPa validates the overall approach. Above 12.5 GPa, the breakdown of the nearly-free-electron model drives a transition of the pure liquid metal towards a less metallic, denser liquid, whose first coordination shell is less compact. Our study unveils the interplay between electronic, structural, and dynamic degrees of freedom along this liquid-liquid phase transition. In view of its electronic nature, we believe that this behavior is general for the first group elements, thus shedding new light into the high-pressure properties of alkali metals.
authors.affiliation: Dipartimento di Fisica, Università di Roma Sapienza, Roma, Italy.
authors.forename: Taras
authors.initials: T
authors.lastname: Bryk
authors.forename: Simone
authors.initials: S
authors.lastname: De Panfilis
authors.forename: Federico A
authors.initials: FA
authors.lastname: Gorelli
authors.forename: Eugene
authors.initials: E
authors.lastname: Gregoryanz
authors.forename: Michael
authors.initials: M
authors.lastname: Krisch
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Ruocco
authors.forename: Mario
authors.initials: M
authors.lastname: Santoro
authors.forename: Tullio
authors.initials: T
authors.lastname: Scopigno
authors.forename: Ari P
authors.initials: AP
authors.lastname: Seitsonen