Physicists discover the “secret source” behind the exotic properties of new quantum materials

Visualization of zero-energy electronic states from Kagome materials studied by MIT’s Riccardo Comin and colleagues-also known as the “Fermi surface”. Credits: Massachusetts Institute of Technology Comin Laboratory

MIT physicists and colleagues have discovered the “secret source” behind some of the exotic properties of new quantum materials that have fixed physicists for these properties, including superconductivity. Theorists have predicted the reasons for the anomalous properties of the material known as Kagome metal, but this is the first time that the phenomena behind these properties have been observed in the laboratory.

“Hope is a new understanding of electronic structure Kagome Metals help us build a rich platform for discovering others Quantum materialHe was an assistant professor of career development in physics at MIT in the 1947 class, and the group led the research. This has the potential to introduce new classes of superconductors, new approaches to quantum computing, and other quantum technologies.

The work is reported in the January 13, 2022 online version of the journal. Nature Physics..

Classical physics can be used to explain many of the underlying phenomena of our world until things get very small. Subatomic particles, such as electrons and quarks, behave differently in ways that are not yet fully understood. Enter quantum mechanics, an area that seeks to explain their behavior and the resulting effects.

Kagome metal, which is at the center of current research, is a new quantum material, or exhibits the exotic properties of quantum mechanics on a macroscopic scale. In 2018, MIT Mitsui Career Development Associate Professors Comin and Joseph Checkelsky led the first research on the electronic structure of Kagome metals, raising interest in this material family. Members of the Kagome Metal family consist of layers of atoms arranged in repeating units similar to the Star of David and the Sheriff’s badge. This pattern is also common in Japanese culture, especially as a basket weaving motif.

“This new family of materials is unconventional, superconducting, nematic, Charge density wave“Comin says.

Abnormal characteristics

A hint of superconductivity and charge density wave ordering for a new family of Kagome metals studied by Comin et al. Was found in the laboratory of Professor Stephen Wilson at the University of California, Santa Barbara. Single crystals were also synthesized there (Wilson said the Nature Physics paper). The specific Kagome material being investigated in the current study is composed of only three elements (cesium, vanadium, antimony) and has a chemical formula of CsV3Sb5.

Researchers have focused on two exotic properties that Kagome metals exhibit when cooled below room temperature. At these temperatures, the electrons in the material begin to exhibit collective behavior. “They don’t move independently, they talk to each other,” says Komin.

One of the resulting properties is superconductivity, which allows the material to conduct electricity very efficiently. In ordinary metal, the electrons behave like people dancing individually in a room. In Kagome superconductors, when the material is cooled to 3 Kelvin (~ -454 degrees Fahrenheit), the electrons start to move in pairs, like a couple of dances. “And all of these pairs are moving together, as if they were part of a quantum choreography,” says Comin.

At 100 Kelvin, the Kagome material studied by Comin and co-workers exhibits yet another strange kind of behavior known as charge density waves. In this case, the electrons are arranged in the shape of ripples like dunes. “They don’t go anywhere. They stay in place,” Komin says. Ripple peaks represent electron-rich regions. The valley is electron deficient. “Charge density waves are very different from superconductors, but they are still a state of matter in which electrons must be arranged in a collective and highly organized manner. They form choreography again, but are no longer dancing. No. Now they form a static pattern. “

Comin states that Kagome metals are of great interest to physicists because they can exhibit both superconducting and charge density waves. “It is unusual for a material to host both, as these two exotic phenomena often compete with each other.”

Secret sauce?

But what’s behind the emergence of these two properties? “What causes electrons to start talking to each other and influencing each other? That’s an important question,” said Mingu Kang, a graduate student in the MIT Physics Department who also belongs to the Max Planck POSTECH Korea Research Initiative. I am saying. .. That’s what physicists report in Nature Physics. “By examining the electronic structure of this new material, we discovered that electrons exhibit an interesting behavior known as electron specificity,” says Kang. This particular singularity is named after Leon van Hove, the Belgian physicist who first discovered it.

The Van Hove singularity contains the relationship between electron energy and velocity. Normally, the energy of a moving particle is proportional to the square of its velocity. “It’s a fundamental pillar of classical physics, [essentially] The faster the speed, the more energy there is. ” Imagine a Red Sox pitcher hitting you with a fastball. Next, imagine your child trying to do the same. Pitcher balls are much more painful than children. There is little energy.

The Comin team has found that with Kagome metal, this rule no longer holds. Instead, electrons moving at different velocities happen to have the same energy. As a result, the pitcher’s fastball has the same physical effect as a child. “It’s very counter-intuitive,” says Comin.He pointed out that it is difficult to relate energy to the velocities of electrons in solids and requires special equipment at two international synchrotron research facilities: Beamline 4A1 of the Urano light source and Lawrence Berkeley. Beamline of Advanced Light Source 7.0.2 (MAESTRO) National Laboratory

Comment Professor Ronny Thomale of the University of Würzburg (Germany): “Theoretical physicists (including my group) predict the unique properties of the Van Hove singularity on the Kagome lattice, which is a crystal structure made up of triangles that share angles. The first experimental validation of these theoretical proposals. “Thomale was not involved in the work.

It is known that if there are many electrons at once in a material with the same energy, they interact much more strongly. As a result of these interactions, the electrons can be paired into superconductivity or otherwise form a charge density wave. “The existence of the Van Hove singularity in materials that have both as a common source of these exotic phenomena makes perfect sense,” Kang adds. “Therefore, the existence of this singularity is the” secret source “that enables the quantum behavior of Kagome metals. “

The team’s new understanding of the relationship between energy and velocity in Kagome materials “is also important because it makes it possible to establish new design principles for the development of new quantum materials,” says Comin. In addition, “We now know how to find this singularity in other systems.”

Direct feedback

When physicists are analyzing data, they often need to process it before they see a clear trend. However, the Kagome system “provided direct feedback on what was happening,” says Comin. “The best part of this study was that we were able to see singularities in the raw data.”

Kagome lattice superconductor reveals “cascade” of quantum electronic states

For more information:
Mingu Kang et al, The origin of the double Van Hove singularity and charge order in the topological Kagome superconductor CsV3Sb5, Nature Physics (2022). DOI: 10.1038 / s41567-021-01451-5

Quote: Physicist, new quantum material obtained on January 13, 2022 from https: // (January 13, 2022) Discover the “secret source” behind the exotic traits of (Sun)

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Physicists discover the “secret source” behind the exotic properties of new quantum materials

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