According to new research, light-induced phase changes behave differently than temperature-induced phase changes. While optically induced phase changes had previously been observed, the mechanism by which they occurred was unknown. More understanding of the process could lead to new optoelectronic devices, such as data storage devices.
The researchers used an electron density modulation frozen within a solid to study light-induced phase change. A charge density wave is an electronic analog that mimics the properties of a crystalline solid.
The researchers discovered that the phase change caused many topological defects in the material during optically induced melting. These defects, which researchers compared to vortices on the surface of the water, altered the dynamics of the material’s electrons and lattice atoms.
The light-induced phase transition occurred quickly, as a piece of semi-molten red-hot iron cools almost instantly when quenched in cold water. The laser pulse used to simulate the phase change was less than one picosecond in length.
The researchers observed the changes in electrons and atoms within the material in response to the laser pulse using a combination of three techniques: ultrafast electron diffraction, transient reflectivity, and time- and angle-resolved photoemission spectroscopy.
During the phase change, the images revealed the formation and propagation of vortex-like topological defects. The researchers could also see the matter resolidifying after the laser pulses stopped.