March 1, 2024

Surprise physics in insulating material offers path to faster technology

This article has been reviewed in accordance with Science X’s editorial process and policies. The editors have highlighted the following attributes, ensuring the credibility of the content:

checked

peer-reviewed publication

trusted source

review


Photoinduced structural change and insulator-metal transition. The, Top left, schematic representation of an epitaxially strained thin film (O, red; Ca, green; Ru, cyan; La, magenta; and Al, gray). On the right, structural phase transformation of S-Pbca (shaded) and L-Pbca (colored). Bottom left, electronic configuration of Ru d orbitals in CatwoRuO4. BPhotoinduced dynamics of the 008 Bragg peak of a strained CatwoRuO4 thin film with pump fluence of 50 mJ cm−2. The peak shifts to a lower momentum transfer qz within 3.3 ps, which indicates an expansion of the network. Line scans show a projection onto qz of the volume of 3D reciprocal space measured by shaking the crystal. wThe time-resolved change in normalized scattering intensity (black circles, incident pump fluence 50 mJ cm−2) into a fixed wave vector, qz= 4.089Å−1increases by about 2.5 ps and persists for τ ≤ 100 ps The time-resolved high-frequency reflectivity (red squares, AND = 1.55 eV, incident pump fluence 0.14 mJ cm−2) increases rapidly, within 1 ps, shows a peak coincident with network expansion, and slowly decays within 100 ps. The signal for the time-resolved low-frequency reflectivity (purple triangles, terahertz bandwidth 0.8 to 10 meV, incident pump fluence 15.1 mJ cm−2) increases by about 8 ps and persists for 100 ps. Time-resolved X-ray data and low-frequency reflectivity were measured after photoexcitation (pump) with a AND = 1.55 eV femtosecond laser. Time-resolved high-frequency reflectivity was measured with a AND = 1.64 eV femtosecond laser. The uncertainty in the X-ray data in w shows the standard deviation of the intensities measured in the ground state for negative delays. Credit: Nature Physics (2024). DOI: 10.1038/s41567-024-02396-1

× to close


Photoinduced structural change and insulator-metal transition. The, Top left, schematic representation of an epitaxially strained thin film (O, red; Ca, green; Ru, cyan; La, magenta; and Al, gray). On the right, structural phase transformation of S-Pbca (shaded) and L-Pbca (colored). Bottom left, electronic configuration of Ru dorbitals in CatwoRuO4. BPhotoinduced dynamics of the 008 Bragg peak of a strained CatwoRuO4 thin film with pump fluence of 50 mJ cm−2. The peak shifts to a lower momentum transfer qz within 3.3 ps, which indicates an expansion of the network. Line scans show a projection onto qz of the volume of 3D reciprocal space measured by shaking the crystal. wThe time-resolved change in normalized scattering intensity (black circles, incident pump fluence 50 mJ cm−2) into a fixed wave vector, qz= 4.089Å−1increases by about 2.5 ps and persists for τ≤ 100 ps The time-resolved high-frequency reflectivity (red squares, AND= 1.55 eV, incident pump fluence 0.14 mJ cm−2) increases rapidly, within 1 ps, shows a peak coincident with network expansion, and slowly decays within 100 ps. The signal for the time-resolved low-frequency reflectivity (purple triangles, terahertz bandwidth 0.8 to 10 meV, incident pump fluence 15.1 mJ cm−2) increases by about 8 ps and persists for 100 ps. Time-resolved X-ray data and low-frequency reflectivity were measured after photoexcitation (pump) with a AND= 1.55 eV femtosecond laser. Time-resolved high-frequency reflectivity was measured with a AND= 1.64 eV femtosecond laser. The uncertainty in the X-ray data in w shows the standard deviation of the intensities measured in the ground state for negative delays. Credit: Nature Physics(2024). DOI: 10.1038/s41567-024-02396-1

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 the unique properties is not fully understood, in part due to the challenging task of imaging the material’s nanostructures in real space and capturing how these structures undergo phase changes in just a trillionth of a second.

A new study published in Nature Physicsunraveled the physics of the Mott, Ca insulatortwoRuO4, as it was stimulated with a laser. In unprecedented detail, the researchers observed interactions between the material’s electrons and the underlying lattice structure, using ultrafast pulses of X-rays to capture “snapshots” of structural changes in Ca.twoRuO4 within critical picoseconds after laser excitation.

The results were unexpected – electronic rearrangements are generally faster than network rearrangements, but the opposite was observed in the experiment.

“Normally, fast electrons respond to stimuli and drag slower atoms with them,” said lead author Anita Verma, a postdoctoral fellow in materials science and engineering. “What we discovered in this work is unusual: the atoms responded faster than the electrons.”

Although researchers aren’t sure why the atomic lattice can move so quickly, one hypothesis is that the material’s nanotexture gives it nucleation points that help reorganize the lattice, similar to the way supercooled ice begins to form. form more quickly around an impurity in the water.

The research builds on a 2023 paper in which Andrej Singer, senior author and assistant professor in materials science and engineering, and other scientists used high-power X-rays, phase recovery algorithms, and machine learning to obtain a view into real space of the same material on a nanoscale.

“Combining the two experiments gave us the idea that in some materials like this, we can change phase very quickly – on the order of 100 times faster than in other materials that don’t have this texture,” Singer said. “We are hopeful that this effect will be a general path to accelerating change and resulting in some interesting applications in the future.”

Singer said that in some Mott insulators, applications include developing materials that are transparent in their insulating state and that quickly become opaque when excited in their metallic state. The underlying physics could also have implications for future, faster electronics.

Singer’s research group plans to continue using the same imaging techniques to investigate new phases of matter that are created when nanotextured thin films are excited with external stimuli.

More information:
Anita Verma et al, Picosecond volume expansion drives a posterior insulator-to-metal transition in a nanotextured Mott insulator, Nature Physics(2024). DOI: 10.1038/s41567-024-02396-1

Diary information:
Nature Physics

Leave a Reply

Your email address will not be published. Required fields are marked *