Strange electronic behavior surprises solid-state physicists

An image captured by laser-PEEM showing the arrangement of electrons in a sample of IBSC material. In this technique, images are taken from laser light illuminating the sample in two different directions. Linear dichroism (LD) refers to the difference between images taken from these two directions of illumination; it allows you to see details that you might not otherwise be able to see, such as in this case the distribution of electrons. Credit: © 2021 Shin et al.

New wave of electronic research

A surprising result for solid-state physicists suggests an unusual behavior of electrons.

While studying the behavior of electrons in iron-based superconducting materials, researchers at the University of Tokyo observed a strange signal related to the way electrons are arranged. The signal involves a new arrangement of electrons that the researchers call a nematicity wave, and they hope to collaborate with theoretical physicists to better understand it. The nematicity wave could help researchers understand how electrons interact with each other in superconductors.

A long-held dream of solid state physicists is to fully understand the phenomenon of superconductivity – essentially electronic conduction without the resistance that creates heat and drains energy. It would usher in a whole new world of incredibly efficient or powerful devices and is already in use on Japan’s Experimental Magnetic Levitation High Speed ​​Train. But there is much to explore in this complex subject, and it often surprises researchers with unexpected findings and observations.

Professor Shik Shin from the Institute of Solids Physics at the University of Tokyo and his team are studying the behavior of electrons in iron-based superconducting materials, or IBSCs. These materials hold great promise as they could operate at higher temperatures than some other superconducting materials, which is of significant concern. They also use components from less exotic materials and can therefore be easier and cheaper to work with. To activate the superconducting capacity of a sample, the material must be cooled to several hundred degrees below zero. And some interesting things are happening during this cooling process.

“As the IBSCs cool down to a certain level, they express a state that we call electronic nematicity,” Shin said. “This is where the material’s crystal lattice and the electrons it contains appear to be arranged differently depending on the angle you look at them, also known as anisotropy. how the electrons are arranged is tightly coupled to the way the surrounding crystal lattice is arranged.But our recent observation shows something very different and indeed quite surprising.


A diagram of the experimental setup developed by the team. Credit: © 2021 Shin et al.

Shin and his team used a special technique developed by their group called laser-PEEM (photoemission electron microscopy) to visualize their IBSC sample at the microscopic scale. They expected to see a familiar pattern that repeats every few nanometers (billion meters). And of course, the crystal lattice showed this pattern. But to their surprise, the team found that the electron pattern instead repeated every few hundred nanometers.

This disparity between the electronic nematicity wave and the crystal structure of the IBSC was unexpected, so its implications are still under investigation. But the result could open the door to theoretical and experimental explorations on a fundamental part of the phenomenon of superconductivity, namely how electrons form pairs at low temperatures. Knowledge of this process could be crucial for the development of high temperature superconductivity. So if the waves of nematicity are related, it is important to know how.

“Then I hope we can work with theoretical physicists to deepen our understanding of nematicity waves,” Shin said. “We also want to use laser-PEEM to study other related materials such as metal oxides like copper oxide. It may not always be clear where the applications lie, but working on fundamental physics problems really fascinates me.

Reference: “Discovery of mesoscopic nematicity wave in iron-based superconductors” by T. Shimojima, Y. Motoyui, T. Taniuchi, C. Bareille, S. Onari, H. Kontani, M. Nakajima, S. Kasahara, T. Shibauchi , Y. Matsuda and S. Shin, September 3, 2021, Science.
DOI: 10.1126 / science.abd6701

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