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Quantum magnet with a topological rotation



The researchers investigated a material that has an internal structure shown in 3D on the left panel consisting of triangles and hexagons located in a pattern similar to the Japanese basket of cahomosh. Copyright: Hasan, et. etc., Princeton University
Taking its name from the tricky Japanese basket, the cagome magnets are considered electronic properties that can be valuable for future quantum devices and applications. Theories suggest that some electrons in these materials have exotic, so-called topological behaviors, while others behave like graphene, another material is valued for its potential for new types of electronics.
Now, an international team led by researchers from Princeton University has noticed that some of the electrons in these magnets behave collectively, as an almost infinitely massive electron, which is amazingly magnetic, and not as individual particles. The study was published in the journal Nature Physics this week.

The group also showed that the placement of a magnet in a high magnetic field causes a reverse direction of magnetism. This "negative magnetism" is similar to a compass that is directed to the south, not to the north, or a fridge magnet that suddenly refuses to hold on.

"We were looking for super-massive" flat "electrons that could still carry electricity for a long time, and finally we found them," said M. Zahid Hassan, Professor of Physics, Eugene Higgins at Princeton University, who led the team. "In this system, we also discovered that due to the internal quantum phase effect, some electrons are opposite to the magnetic field, producing negative magnetism."

The team investigated how the atoms located in the cohome in the crystal give rise to strange electronic properties which mo It is terrible to have real advantages, such as superconductivity, which allows electricity to flow without loss as heat, or magnetism that can be controlled at a quantum level for use in future electronics.

modern scanning tunneling microscopy and spectroscopy (STM / S) to look at the behavior of electrons in a crystal with a cagome pattern made of cobalt and tin, fixed between two layers of sulfur atoms, which are further fixed between two layers. In the layer of cogoms, the atoms of cobalt form triangles around the six-member a tin bond with a tin atom in the center. This geometry forces electrons to get into some awkward positions ̵

1; this leads to the fact that this type of material is called "disappointed magnet".

To investigate the behavior of electrons in this structure, researchers have touched the upper layers to reveal a layer of cagomas under it. 19659011] Then they used the STM / S technique to detect the energy profile of each electronic or band structure. The strip structure describes the range of energies an electron can have within the crystal, and explains, for example, why some materials spend electricity, while others are isolators. The researchers found that some electrons in the cohome layer have a strip structure which, instead of being curvilinear, is, as in most materials, flat.

Although it is expected that the electrons in the magnet directed north move upward when exposed to the magnetic field up, the electrons of the kagomas actually move downwards (left panel). The application of the magnetic field shifts the energy levels of the electrons (middle panel). The energy shifts of cations' electrons show a large negative magnetic moment (on the right, on top). The orbital apparatuses of the caho electrons give rise to a geometric phase phase factor (right, above), known as the Yagod phase, which creates an unusual magnetic state. Author: Hassan et al., Princeton University
The structure with a flat band indicates that the electrons have an effective mass that is so large that it is almost infinite. In this state, the particles act collectively, and not as separate particles.

Theories have long predicted that the Kagoma model will create a structure with a flat band, but this study is the first experimental detection of an electron of a planar zone in such a system.

One of the following general assumptions is that a material with a flat band may exhibit negative magnetism.

Indeed, in this study, when researchers applied a strong magnetic field, some electromagnets of the magnet cahome were pointed in the opposite direction.

"Whether the field was applied up or down, the energy of the electrons turned over in the same direction, this was the first thing that was strange in terms of experiments," said Santian Sonia Zhang, a graduate student in physics and one of three co-authors on paper .

"It puzzled us about three months," said Jia-Xin Yin, Ph.D., and another co-author of the study. "We were looking for a reason, and with our collaborators, we realized that this is the first experimental proof that this peak of the plane band in the cagom lattice has a negative magnetic moment."

The researchers found that negative magnetism arises due to the relationship between the plane band of the kagome, a quantum phenomenon called spin-orbit magnetism, magnetism, and a quantum factor called the Burry curvature field. The spin-orbital relation relates to the situation when the spin of an electron, which itself is the quantum property of electrons, becomes rolled up electrons. The combination of the spin-orbit bond and the magnetic nature of the material leads to the fact that all electrons behave in the blocking step as a gigantic single particle. topological behavior. Subject to the Nobel Prize in Physics, 2016, topological materials may have electrons that proceed without resistance on their surfaces and are an active area of ​​research. An example of a topological system is cobalt-tin-sulfur

. Two-dimensional lattice grids may have other desired types of electron conductivity. For example, graphene is the structure of carbon atoms, which has been of considerable interest for its electronic applications over the past two decades. The structure of the Kagome zone lattice generates electrons that behave like those in graphene.

Research, "Negative magnetism with a flat band in a spin-orbit correlated magnet of Caho", Jia-Xin Yin, Songtian S. Zhang Zhang, Qi Wang, Stepan S. Zircin, Zurab Guguchiya, Biao Lian, Hubang Zhou, Kun Jiang, Ilya Belopolsky, Nana Shumiya, Daniel Malter, Maxim Litskevich, Tyler A. Kochran, Xin Ling, Z. Vang, Titus Neuperth, Hechang Lei and M. Zahid Hasan, were published on the Internet on February 18, 2019 in the journal Nature Physics .


Explore further:
A new "rotation" on the cogome racks

Additional information:
Jia-Xin Yin et al., Negative magnetism of a flat band in a spin-orbit correlated magnet of cahom, Nature Physics (2019). DOI: 10.1038 / s41567-019-0426-7

Reference of the journal:
Physics of nature

Granted:
Princeton University


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