× close
Photo-induced structural changes and insulator-to-metal transitions. be, Top left, schematic diagram of the epitaxially strained thin film (O, red; Ca, green; Ru, cyan; La, magenta; Al, gray).Right, from structural phase transition S-Pbca (shaded) and L-Pbca (Colored).Bottom left, electron configuration of Ru dOrbital of Ca2LuoFour. bphotoinduced dynamics of the 008 Bragg peak in strained Ca2LuoFour Thin membrane at a pump fluence of 50 mJ cm−2.The peak shifts towards lower momentum transfer qz Within 3.3 ps, this indicates lattice expansion.Line scan shows projection upwards qz 3D reciprocal space volume measured by rocking a crystal. ctime-resolved changes in normalized scattering intensity (black circles, incident pump fluence 50 mJ cm2)−2) with a fixed wavenumber vector, qz= 4.089Å−1increases and persists at approximately 2.5 ps. τLess than 100ps. Time-resolved high-frequency reflectance (red squares, E= 1.55 eV, incident pump fluence 0.14 mJ cm−2) increases rapidly within 1 ps, exhibits a peak consistent with lattice expansion, and decays slowly within 100 ps. Time-resolved low-frequency reflectance signal (purple triangles, terahertz bandwidth 0.8 to 10 meV, incident pump fluence 15.1 mJ cm−2) increases within about 8 ps and lasts for 100 ps. Time-resolved X-ray data and low-frequency reflectance were measured after optical excitation (pump). E= 1.55 eV femtosecond laser. The time-resolved high frequency reflectance is E= 1.64 eV femtosecond laser. Uncertainty in X-ray data c Shows the standard deviation of the intensity measured in the ground state for negative time delays. credit: natural physics(2024). DOI: 10.1038/s41567-024-02396-1
Researchers led by Cornell University have discovered an unusual phenomenon in metallic insulating materials, providing valuable insight into the design of materials with new properties due to faster switching between states of matter.
Mott insulators are a group of materials with unique electronic properties, including those that can be manipulated by stimuli such as light. The origin of the unique properties is not completely understood. Part of the reason is the difficult task of imaging nanostructures in materials in real space and capturing how these structures undergo phase changes at trillionths of a second.
new research published in natural physicsElucidated the physics of Mott insulator Ca2LuoFourDue to laser stimulation. Researchers used ultrafast X-ray pulses to capture ‘snapshots’ of structural changes in Ca, allowing them to observe interactions between the material’s electrons and the underlying lattice structure in unprecedented detail. .2LuoFour within critical picoseconds after excitation by the laser.
The results were unexpected. Although electronic rearrangements are generally faster than lattice rearrangements, the opposite was observed in experiments.
“Normally, fast electrons respond to a stimulus and drag slower atoms with them,” said lead author Anita Verma, a postdoctoral researcher in materials science and engineering. “What we discovered in this study was unusual: atoms reacted faster than electrons.”
Researchers don’t know why the atomic lattice can move so quickly, but just as supercooled ice begins to form earliest around impurities in water, the material’s nanotexture helps the lattice move. There is a hypothesis that it provides nucleation points that help the rearrangement of
The research, in which Andrei Singer, senior author and assistant professor of materials science and engineering, and other scientists used high-power X-rays, phase retrieval algorithms, and machine learning to achieve real-space visualization. Based on a paper. The same material is used at the nanoscale.
“Combining the two experiments gave us the insight that some materials like this can switch phases very quickly, 100 times faster than other materials that don’t have this texture. That’s on the order of double,” Singer said. “We hope that this effect will become a common route to speed up switching, leading to interesting applications in the future.”
For some Mott insulators, applications include developing materials that are transparent in the insulating state and quickly become opaque when excited to the metallic state, Singer said. The underlying physics could also influence faster electronics in the future.
Singer’s research group plans to continue using the same imaging techniques to investigate new phases of matter that are produced when nanotextured thin films are excited with external stimuli.
For more information:
Anita Verma et al, Picosecond volume expansion promotes subsequent insulator-metal transition in nanotextured Mott insulators. natural physics(2024). DOI: 10.1038/s41567-024-02396-1
