Intrinsic Localized Modes Observed in the High Temperature Vibrational Spectrum of NaI

TL;DR

This study reports the observation of intrinsic localized vibrational modes in NaI at high temperatures, revealing their characteristics and creation energy through neutron and x-ray scattering techniques.

Contribution

It provides the first experimental evidence of three-dimensional intrinsic localized modes in NaI and measures their creation energy.

Findings

Localized mode appears near phonon gap center at 555 K

Mode intensity increases with temperature

Creation energy of the mode is 299 meV

Abstract

Inelastic neutron measurements of the high-temperature lattice excitations in NaI show that in thermal equilibrium at 555 K an intrinsic mode, localized in three dimensions, occurs at a single frequency near the center of the spectral phonon gap, polarized along [111]. At higher temperatures the intrinsic localized mode gains intensity. Higher energy inelastic neutron and x-ray scattering measurements on a room-temperature NaI crystal indicate that the creation energy of the ground state of the intrinsic localized mode is 299 meV.