Shulou(Shulou.com)05/31 Report--

Researchers at Brown University have demonstrated in experiments how a strange material called Mott insulator produces a unique form of magnetism. These discoveries are a step towards a better understanding of the quantum states of these materials and have aroused great interest among scientists in recent years.

The study, published in the journal Nature Communications, helps confirm new theoretical work and attempts to explain the behavior of electrons in these strange materials. The work was done in collaboration with scientists at Stanford University and the National strong Magnetic Field Laboratory.

"We find this theory very reasonable," said VesnaMitrovi, an associate professor of physics at Brown University who led the work. "this shows that this new theory is based on quantum models involving complex electron spin interactions, which is a good start for understanding magnetism in strongly interacting materials."

Mott insulator is a kind of material that is supposed to be a conductor according to traditional conductive theory, but it still acts as an insulator. The insulation occurs because the electrons in these materials have strong correlation and repulsion. This dynamic causes electronic traffic jams and prevents particles from flowing to form an electric current. Scientists hope they can find a way to move these materials into and out of Mott's insulation, which is very useful for the development of new functional devices. It has also been found that by introducing impurities into their structures, some Mott insulators become high-temperature superconductors-materials that conduct without resistance at much higher temperatures than are normally required for superconductivity.

Despite the prospect of these materials, scientists still do not fully understand how they work. A complete description of the electronic state in these materials has been elusive. At the most basic level, each individual electron is characterized by its charge and spin, and its tiny magnetic moment points up or down. The electronic properties of Mott insulators are difficult to predict because the states of electrons are closely related to each other-the state of one electron affects the state of its neighbors.

To make matters more complicated, many Mott insulators exhibit so-called spin-orbit coupling, which means that the spin of each electron varies with the orbital motion of the nucleus. Spin-orbit coupling means that the magnetic moment of an electron is affected by its orbit around the nucleus, so the spin of an electron is not well defined. Therefore, in order to predict the properties of these materials, we need to know the interaction between electrons, and the basic properties of individual electrons depend on their orbital motion.

"when you have these complex interactions and spin coupling, it becomes very complicated to describe it in theory," Mitrovic said. " However, we need such a basic quantum theory to predict and utilize the new quantum properties of complex materials. "

Mitrovi's research focuses on a strange magnetism that occurs when a Mott insulator with strong spin-orbit coupling cools below the critical temperature. Magnetism is caused by the arrangement between electron spins. In this case, however, because the spin interactions are strong and their values depend on orbital motion, it is not known how these magnetism are generated in these materials.

There is an important theoretical attempt to show what might happen to these materials at the most basic level in order to achieve this magnetic state. This is what Mitrovic and her colleagues want to test.

Mitrovi colleagues at Stanford University first synthesized and characterized Mott insulating materials consisting of barium, sodium, osmium and oxygen, which were tested by nuclear magnetic resonance (NMR). The team used special techniques that enabled them to collect information about the distribution of electron charges and electron spins in materials.

The results show that with the cooling of the material, the change of the electron charge distribution will cause the distortion of the atomic orbital and lattice. As the temperature cools further, this deformation drives magnetism by causing electron spin arrangement in each layer of the atomic lattice.

"We can determine the exact nature of the orbital charge distortion and the exact spin arrangement in this strange magnetic state before the magnetic force." Mitrovic said. "in one layer, your rotation is aligned in one direction, and then in the layers above and below it, the rotation is aligned in different directions. Although each layer has strong magnetism, all the magnetic fields are weak."

Mitrovic's theory is studying and predicting that this layered magnetism just precedes charge distortion. Therefore, these findings help to confirm that the theory is correct.

Mitrovic says the work is an important step in understanding and manipulating the nature of this interesting material for practical application. In particular, materials with spin-stage coupling are expected to be used to develop electronic devices that consume less power than ordinary devices.

"if we want to start using these materials in equipment, we need to have a basic understanding of how they work," Mitrovic said. " In this way, we can adjust the properties according to our own needs. By verifying some of the theoretical work of Mott insulators with strong spin-orbit coupling, this work is an important step towards better understanding. "

In a broader sense, this work is a step towards a more comprehensive magnetic quantum theory.

Mitrovica said: "although magnetism is the longest known quantum phenomenon discovered by the ancient Greeks, the basic quantum theory of magnetism is still elusive." The work we designed is to test a new theory and to try to explain how magnetic forces are generated in foreign materials. "

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