A team of researchers in Japan has now uncovered how electric currents move through a particular category of these materials, known as kagome metals. Their study revealed for the first time that even weak magnetic fields can reverse tiny circulating electrical currents inside the metal. This reversal changes how easily current flows depending on direction, producing what scientists call the diode effect -- where electricity passes more freely one way than the other.

The researchers also found that quantum geometric properties amplify this effect by roughly 100 times. Their findings, published inProceedings of the National Academy of Sciences, establish the theoretical foundation for future electronic technologies that could be tuned or switched using simple magnetic fields.

Since around 2020, scientists have observed this type of magnetic switching in experiments but could not explain the mechanism or why the effect was so pronounced. The new research offers the first complete theoretical explanation for both.

When electrons become "frustrated"

The term "kagome metal" comes from the Japanese word "kagome," meaning "basket eyes" or "basket pattern," inspired by a traditional bamboo weaving technique that creates interlocking triangles.

In these materials, atoms adopt the same distinctive triangular arrangement. This geometry causes what physicists describe as "geometric frustration," a condition where electrons cannot settle into neat, orderly arrangements. Instead, they form intricate quantum states that include the circulating electrical loops observed in experiments.

When the direction of these loops reverses, the way electricity travels through the metal also changes. The team discovered that these circulating currents interact with wave-like electron patterns (known as charge density waves), disrupting key symmetries in the metal's electronic structure. They further showed that quantum geometric effects -- phenomena that appear only at the smallest scales -- intensify this switching behavior dramatically.

"Every time we saw the magnetic switching, we knew something extraordinary was happening, but we couldn't explain why," Hiroshi Kontani, senior author and professor from the Graduate School of Science at Nagoya University, recalled.

"Kagome metals have built-in amplifiers that make the quantum effects much stronger than they would be in ordinary metals. The combination of their crystal structure and electronic behavior allows them to break certain core rules of physics simultaneously, a phenomenon known as spontaneous symmetry breaking. This is extremely rare in nature and explains why the effect is so powerful."

To perform the experiments, the researchers cooled the metals to about -190°C. At this temperature, kagome metals naturally develop quantum states where electrons move in tiny loops, generating wave-like patterns throughout the material. When weak magnetic fields are applied, these circular currents reverse direction, flipping the preferred flow of electric current in the process.

New materials meet new theory

This breakthrough in quantum physics was not possible until recently because kagome metals were only discovered around 2020. While scientists quickly observed the mysterious electrical switching effect in experiments, they could not explain how it worked.

The quantum interactions involved are very complex and require advanced understanding of how loop currents, quantum geometry, and magnetic fields work together -- knowledge that has only developed in recent years. These effects are also very sensitive to impurities, strain, and external conditions, which makes them difficult to study.

"This discovery happened because three things came together at just the right time: we finally had the new materials, the advanced theories to understand them, and the high-tech equipment to study them properly. None of these existed together until very recently, which is why no one could solve this puzzle before now," Professor Kontani added.

"The magnetic control of electrical properties in these metals could potentially enable new types of magnetic memory devices or ultra-sensitive sensors. Our study provides the fundamental understanding needed to begin developing the next generation of quantum-controlled technology," he said.

• RELATED TOPICS
  • Matter & Energy
    • Physics
    • Materials Science
    • Nature of Water
    • Electricity
  • Computers & Math
    • Spintronics Research
    • Artificial Intelligence
    • Hacking
    • Encryption

• RELATED TERMS
  • Quantum computer
  • Introduction to quantum mechanics
  • Metal
  • Electron configuration
  • Physics
  • Breaking wave
  • Nanoparticle
  • Quantum dot