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Breakthrough! Chinese scientists discover new magneton state that may be used in chips and radar

The discovery by Prof. Lu Wei's team breaks through the category of "Walker modes", which has monopolized the field for more than 60 years, and uncovers new magneton states that may be used in radar, communication, and wireless transmission of information.

On March 10, the official website of University of Shanghai for Science and Technology (USST) announced that Professor Lu Wei's group in the School of Material Science and Technology of USST has recently made important progress in the direction of photon-magnet interaction and strong coupling regulation. For the first time, the research team discovered a new magnetic resonance in a single crystal of ferromagnetic insulator, named pump-induced magnon mode (PIM). This discovery opens up a whole new dimension for the study of magnetoelectronics and quantum magnetism.

The results were published in Physical Review Letters, the flagship journal in the field of physics.

The title of the paper is "Unveiling a Pump-Induced Magnon Mode via Its Strong Interaction with Walker Modes".

According to the news, the discovery by Prof. Lu Wei's team breaks through the category of "Walker modes" that has "monopolized" the field for more than 60 years, and uncovers new magneton states that may be used in the fields of radar, communication, and wireless transmission of information.

New Magneton States

In 1956, L. R. Walker, a staff member at Bell Telephone Laboratories in New Jersey, USA, wrote a paper giving a mathematical description of the spatially confined magneton state of a magnetic bulk, which was subsequently published and became known as the Walker modes. The field.

The article "Topological states and quantum effects in magneton", a review article published in the Chinese academic journal "Journal of Physics" in 2023 by Professor Peng Yan and others in the School of Physics and State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology, introduces the quantumized spin wave called magneton (magnon).

The spin wave, a collective excited state of spin progression in the magnetic system, was first proposed by physicist Bloch (1952 Nobel Prize winner) in 1930 to explain the important law of temperature dependence of the spontaneous magnetization strength of ferromagnets, and was subsequently confirmed by physicist Brockhouse in 1957, 1994 Nobel laureate in physics) using inelastic neutron scattering experiments.

The wavelength of spin waves can be as small as a few nanometers, which can increase the information storage density and facilitate the miniaturization and high integration of magnetron devices. Moreover, spin wave transmission does not involve the motion of electrons and can propagate in both magnetic metals and magnetic insulators, avoiding the power consumption due to Joule heat.

Each magneton carries a spin angular momentum that approximates Planck's constant, so that magnetons can carry and transmit spin information just like electrons. The main purpose of magnetonics is to replace the information carriers with spin waves for information transfer and logical computation. Previously, the information carrier was the charge or spin property of the electron.

The aforementioned news from the University of Science and Technology of Shanghai says that the magneton state is a central concept in the application of electron spin, which is the collective excitation of spins in magnetic materials. The origin of macroscopic magnetism is mainly the unpaired electrons in the material. Electrons have two well-known fundamental properties: charge and spin. The former is the object of manipulation by all electronic devices. The spin, especially in magnetic insulators, can completely avoid the ohmic loss of conduction electrons and take full advantage of the long lifetime and low dissipation of spin, and is therefore of great significance for the development of spintronics devices. Magnetons can also interact with superconducting quantum bits and play an important role in quantum information technology.

The newly published study found that when a ferromagnetic insulator single crystal sphere is subjected to strong microwave excitation at low magnetic fields, the unsaturated spins inside will gain some synergy and generate a spin wave oscillating at the same frequency as the microwave excitation signal, which can be named as "pump-induced magnon mode (PIM)". ".

The photoinduced magneton state is like a "dark" state that cannot be directly observed by conventional detection methods, but can be indirectly observed through the energy level splitting produced by its strong coupling with Walker modes and can be modulated by excitation microwaves.

Schematic diagram of the spin of an electron: upper spin (left) and lower spin (right). From the article "Quantum mechanics of migratory birds: spin, entangled states and geomagnetic navigation".

According to the introduction of "electron spin" on the website of the Institute of High Energy Physics, Chinese Academy of Sciences, the concept of spin was introduced for the needs of quantum field theory. Not only the electron has spin, but all microscopic particles such as neutrons, protons and photons have spin, but they take different values. Spin, like static mass and charge, is a physical quantity that describes the inherent properties of a microscopic particle. A particle with spin 0 is like a dot: it looks the same from any direction. A particle with spin 1 is like an arrow: it looks different from different directions.

Spin is different from rotation. The article "Quantum mechanics of migratory birds: spin, entangled states and geomagnetic navigation" published by the WeChat public number of the Institute of High Energy Physics of the Chinese Academy of Sciences introduces that we cannot understand spin from a classical point of view. Current theories and experiments have not found a lower limit on the radius of the electron, and therefore the electron is treated as a point particle. According to the bubbly incompatibility principle, two electrons cannot be in the same state, so the electrons around the nucleus are generally distributed in pairs, and an atomic orbital can hold two electrons, one spin up and one spin down. These two electrons cannot have the same spin orientation and are in an associated state, which is commonly referred to as quantum entangled state.

Excited state is used to describe the state in which an electron is excited to a higher energy level after the absorption of energy by an atom, molecule, etc. Thereafter, the electron may leap to a lower energy level for a short time, releasing some energy, such as releasing a photon, or returning to the ground state.

No electronic noise, can be used for radar precision detection

Shanghai University of Science and Technology said that the development of chips mainly follows Moore's Law, that is, every 18 months to two years, the chip performance will double. However, as human society is gradually entering the post-Moore era, the persistent reduction of the chip process has been "challenged by the limit". Processor performance doubling time is extended, the momentum of the "wild ride" has encountered a technical bottleneck. Driven by market demand, there is an urgent need for "fresh blood" to activate the low-power, highly integrated, high information density information processing carrier way out. The rapid development of spintronics and magnetron electronics based on the development of magnetic materials provides a way out of these limitations.

The team also found that the newly published photo-induced magneton state has a rich nonlinearity, and this nonlinearity produces a magneton frequency comb.

Frequency comb (top). Schematic diagram of a spin wave frequency comb generated by nonlinear magnon-skyrmion scattering (magnon-skyrmion scattering). From "Magnonic Frequency Comb through Nonlinear Magnon-Skyrmion Scattering".

Compared to the frequency combs generated in microwave resonant circuits, this new frequency comb is free of electronic noise and is therefore expected to achieve ultra-low noise signal conversion in information technology.

"Conventional magneton strongly coupled states depend on resonant cavities in order to be constructed ...... We get rid of this dependence and can generate magneton strongly coupled states by the induction of external microwaves. Such coupled states under open boundaries are expected to be ordered and combined like Lego to obtain rich functionality." Team leader Prof. Lu Wei said.

Lu Wei said, "The frequency comb we found is in the microwave band, which is the frequency band used for radar, communications, and wireless transmission of information, and it is predictable that our frequency comb will certainly be useful in these areas."

Lu Wei explains that a frequency comb is like a vernier caliper, capable of making precise measurements of wind and wind in the frequency spectrum. Optical frequency combs (optical frequency combs) have previously been discovered to show amazing accuracy in atomic clocks and ultra-sensitive detection.

The research work was co-authored by University of Shanghai for Science and Technology (USST), Shanghai Institute of Technology and Physics (SITP), Chinese Academy of Sciences (CAS), and Huazhong University of Science and Technology (HUST), with USST as the first author. The first author of the paper is Jinwei Rao, an assistant researcher in the School of Matter of USST, and the corresponding authors are Professor Wei Lu from the School of Matter of USST, Associate Researcher Bi-Ling Yao from the Shanghai Institute of Technology and Physics, Chinese Academy of Sciences, and Professor Tao Yu from Huazhong University of Science and Technology.

Link to the paper.




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