In basic materials like metals, insulators, and semiconductors, the macroscopic properties remain largely unchanged even with minor atomic-level modifications. For example, metals remain conductive, and insulators remain non-conductive. However, in more complex materials that can only be synthesized in laboratories, slight atomic-level changes can lead to drastic macroscopic effects. These advanced materials may transition from insulators to superconductors, conducting electricity without heat loss. Such transitions can occur within picoseconds-a trillionth of a second. To put it in perspective, a picosecond is to a blink of an eye what a blink of an eye is to over 3000 years.
Tracking Electron Collective Movements
Loth's team has developed a technique to observe the behaviors of these advanced materials during atomic-level changes. They focused on a material composed of niobium and selenium, where they could observe the collective motion of electrons in a charge density wave. By introducing a single impurity, they studied how it disrupts this collective movement. The researchers applied a picosecond-long electrical pulse to the material, causing nanometer-scale distortions in the electron collective. This resulted in complex electron motion within the material. Preliminary work for these findings was conducted at the Max Planck Institute for Solid State Research (MPI FKF) in Stuttgart and the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg, where Loth previously conducted research.
Engineering Materials with Precision
"If we can understand how the movement of the electron collective is stopped, then we can also develop materials with desired properties in a more targeted manner," Loth explains the potential of the results. The microscopy method developed helps understand the impact of impurities on material properties, allowing for precise engineering at the atomic level. This understanding could lead to the development of ultra-fast switching materials for future sensors or electronic components. "Design at the atomic level has a direct impact on the macroscopic properties of the material," says Loth.
High-Frequency Experimentation
"There are established methods for visualizing individual atoms or their movements," explains Loth. "But with these methods, you can either achieve a high spatial resolution or a high temporal resolution." To achieve both, Loth's team combined a scanning tunneling microscope, which resolves materials at the atomic level, with ultrafast pump-probe spectroscopy.
The laboratory setup required for these measurements must be extremely well-shielded from vibrations, noise, and air movement, as well as fluctuations in temperature and humidity. "This is because we measure extremely weak signals that are otherwise easily lost in the background noise," Loth points out. The team repeated the measurements frequently to obtain meaningful results, optimizing their microscope to perform the experiment 41 million times per second, achieving high signal quality. "Only we have managed to do this so far," says Loth.
Research Report:Breakthrough in quantum microscopy: Stuttgart researchers are making electrons visible in slow motion
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