title: Thermally triggered phononic gaps in liquids at THz scale.
abstract: In this paper we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to the transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials.
authors.affiliation: National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Dima
authors.initials: D
authors.lastname: Bolmatov
authors.affiliation: National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Zhernenkov
authors.affiliation: Volgograd State Technical University, Volgograd, 400005 Russia.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Zav'yalov
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Stoupin
authors.affiliation: National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Cunsolo
authors.affiliation: National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Yong Q
authors.initials: YQ
authors.lastname: Cai