Turning the heat on organizing energy

June 14, 2011

Turning the heat on organizing energy

Conventional wisdom suggests that when exposing a crystal to heat, the thermal energy within the crystal would spread uniformly across the lattice.

However, physicists have found that unlike the surface of water disturbed by a rock where energy spreads out in ripples, energy in a crystal can spontaneously localize in distinct nonlinear modes. Not only that, but now Lawrence Livermore scientists report that this energy found in intrinsic localized modes (ILMs) as they are called, also can organize into complex and changing dynamical patterns when heated to between 614 and 636 kelvin (water boils at 373 kelvin).

The scientific community expected that ILMs formed randomly throughout a crystal. But the new research by LLNL's Michael Manley and collaborators from Oak Ridge National Laboratory and Cornell University found that ILMs organize into complex and changing patterns.

Using scattering neutrons to probe a sodium iodide crystal, Manley and colleagues found that between 614 and 636 kelvin, the ILMs began switching as a unit from one pattern to another and then would return to their original organization as the crystal was subjected to further heating.

"Although dynamical patterns like this have been known for more than 100 years, this is the first observation in an atomic lattice and the first in thermal equilibrium," Manley said. "It was a big surprise that energy organized in equilibrium. It goes outside of how we treat equilibrium."

ILMs may play an important role in advanced photonic switching devices; energy transport and storage processes in biopolymers; "unzipping" of DNA; and folding of proteins.

"This new understanding is of practical importance since it occurs in ordinary crystals at temperatures where materials are used," Manley said. "It may be of special importance in applications where the flow of thermal energy is critical, such as with thermoelectric materials."

The research appears in the June 14 issue of the new journal, Scientific Reports (Nature's open access journal). The paper can be accessed for free on the Scientific Reports Website.