Solitons show up in uranium
Apr 4, 2006
Scientists have observed highly localized solitary vibrations, or solitons, in a three-dimensional solid for the first time. The solitons exist in crystals of uranium heated to temperatures of 450K. Although they were predicted to exist in 3D solids some 20 years ago, conclusive evidence for them has never been obtained until now (Phys. Rev. Lett. 96 125501).
Solitons are stable localized waves that propagate through a medium without spreading. They were first observed by the Scottish scientist John Scott Russell in 1834, who was watching horses drag a barge along a canal. When the boat suddenly stopped, a wave of water continued along the canal without changing shape or slowing down.
Michael Manley of the Los Alamos National Laboratory and colleagues in the US and Germany have now observed solitons in crystals of uranium. The team obtained its results by firing beams of neutrons and X-rays into the material, which create or absorb vibrational energy from the crystal. They were then able to determine the frequency and wavelength of the crystal's vibrations, or phonons, by measuring the properties of the scattered beam.
When the crystal was heated to 450K, Manley and co-workers found a new type of long-lasting phonon that does not spread throughout the crystal. The team found that the vibrations, which have a wavelength as small as the spacing between two atoms in the crystal, form randomly throughout the material. "The vibration was not allowed by the long range crystal symmetry, indicating that there was a local break in the symmetry, which told us that it was localized", Manley told PhysicsWeb.
Solitons have broad implications from everything from devices that make use of localized energy waves to new bond breaking mechanisms in biological processes. "However, my interest at the moment is trying to understand how solitons change the mechanical properties of materials," says Manley. "Our understanding of mechanical deformation is based on the movement of crystal defects. These localized vibrations are, in effect, a new kind of defect and they seem to play a role in determining the deformability of uranium."
About the author
Belle Dumé is science writer at PhysicsWeb