Cornell-led researchers have discovered an unusual phenomenon in a metallic insulating material, providing valuable information for designing materials with new properties through faster switching between states of matter.
Mott insulators are a family of materials with unique electronic properties, including those that can be manipulated by stimuli such as light. The origin of these unique properties is not fully understood, in part because of the difficult task of imaging the material’s nanostructures in real space and capturing how these structures undergo phase changes as fast as a trillionth of a second.
A new study published in Natural physicsrevealed the physics of Mott insulation, Ca2RuO4, because it was stimulated by a laser. In unprecedented detail, the researchers observed interactions between the material’s electrons and the underlying lattice structure, using ultrafast X-ray pulses to capture “snapshots” of structural changes in the Ca.2RuO4 in the critical picoseconds after excitation with the laser.
The results were unexpected: electronic rearrangements are generally faster than lattice ones, but the opposite was observed in the experiment.
“In general, fast electrons respond to stimuli and drag slower atoms with them,” said lead author Anita Verma, a postdoctoral researcher in materials science and engineering. “What we discovered in this work is unusual: atoms react more quickly than electrons.”
Although researchers don’t know exactly why the atomic lattice can move so quickly, one hypothesis is that the nanotexture of the material gives it nucleation points that help rearrange the lattice, in the same way that supercooled ice begins to coalesce. form more quickly around an impurity in water.
The research builds on a 2023 paper in which Andrej Singer, lead author and assistant professor of materials science and engineering, and other scientists used high-power X-rays, phase recovery algorithms and machine learning to achieve real-space visualization of the same material at the nanoscale.
“The combination of the two experiments allowed us to understand that in certain materials like this we can change phase very quickly, on the order of 100 times faster than in other materials that do not have this texture ” Singer said. “We hope this effect will provide a general pathway to accelerate switching and lead to interesting applications in the future.”
Singer said that in some Mott insulators, applications include materials becoming transparent in their insulating state, then quickly becoming opaque once excited into their metallic state. The underlying physics could also have implications for faster future electronics.
Singer’s research group plans to continue using the same imaging techniques to study new phases of matter created when nanotextured thin films are excited by external stimuli.
More information:
Anita Verma et al, Picosecond volume expansion drives subsequent insulator-to-metal transition in a nano-textured Mott insulator, Natural physics(2024). DOI: 10.1038/s41567-024-02396-1
Provided by Cornell University
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