Researchers led by Cornell have discovered an unusual phenomenon in a metal-insulating material, providing valuable insights for the design of materials with new properties by way of faster switching between states of matter.

Mott insulators are a family of materials with unique electronic properties, including ones that can be manipulated by stimuli such as light. The origin of the unique properties is not fully understood, partly due to the challenging task of imaging the material's nanostructures in real-space and capturing how these structures undergo phase changes in as fast as a trillionth of a second.

A new study published in Nature Physics unraveled the physics of the Mott insulator, Ca2RuO4, as it was stimulated with a laser. In unprecedented detail, researchers observed interactions between the material's electrons and underlying , using ultrafast X-ray pulses to capture "snapshots" of structural changes in the Ca2RuO4 within critical picoseconds after excitation with the laser.

The results were unexpected—electronic rearrangements are generically faster than lattice ones, but the opposite was observed in the experiment.

"Typically, the fast electrons respond to stimuli and drag the slower atoms with them," said lead author Anita Verma, postdoctoral scholar in materials science and engineering. "What we found in this work is unusual: The atoms responded faster than electrons."

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