Synopsis: Solitons in an ionic crystal

Neutron scattering measurements indicate that intrinsic localized modes are found in thermal equilibrium in NaI, a simple ionic crystal.
Synopsis figure

Solitons are localized wave packets with finite energy that retain their shape over time. They are ubiquitous in driven nonlinear systems that are out of equilibrium, including optical fibers, magnets, micromechanical systems, and Josephson junctions. A long-standing question has been whether such modes exist in real solids at thermal equilibrium. The presence of these so-called “intrinsic localized modes” (ILMs) was first proposed in the 1980s, and many theoretical models have made similar predictions for solids that have a significant lattice anharmonicity, but experimental evidence has been lacking.

In an article appearing in Physical Review B, Michael Manley from Lawrence Livermore National Laboratory and collaborators from several other national laboratories and universities show that NaI, a simple three-dimensional ionic crystal, can support a single intrinsic localized mode in thermal equilibrium above 555 K. Inelastic neutron scattering measurements on both powders and single crystals show that the localized mode occurs at a single frequency of 299 meV, which lies near the center of a gap in the phonon spectrum. This mode’s energy does not depend on its wave vector, as expected of an ILM, and the mode gains energy with increasing temperature. These findings present the first observation of a three-dimensional intrinsic localized mode in a crystalline solid, and suggest an important role for such modes in the high-temperature physical properties of solids. – Sarma Kancharla


Announcements

More Announcements »

Subject Areas

Nonlinear DynamicsMaterials Science

Previous Synopsis

Related Articles

Focus: Complex Crystals Form from Heterogeneous Particles
Materials Science

Focus: Complex Crystals Form from Heterogeneous Particles

A suspension containing particles with wide-ranging diameters can crystallize into multiple ordered structures. Read More »

Synopsis: Glassy Fingerprints
Condensed Matter Physics

Synopsis: Glassy Fingerprints

The local structure of glasses and other disordered materials could be extracted from diffraction patterns, according to a proposal for a new technique. Read More »

Synopsis: Electron–Phonon Affair Comes to Light
Condensed Matter Physics

Synopsis: Electron–Phonon Affair Comes to Light

Photoelectron spectroscopy reveals the details of the interaction between electronic and vibrational excitations in a molecular material. Read More »

More Articles