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Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar structures can be observed in magnetic materials.

Magnetic whirls are formed when the magnetic moments are aligned in a circular fashion. These so-called skyrmions are not just interesting for basic research -- because of their stability and their tiny dimensions they could prove crucial for the development of future magnetic storage.

For these reasons they are currently at the center of a large body of research. One of the key questions is about when and how they occur. A team of researchers from Technical University of Munich (TUM), Technical University of Dresden and the University of Cologne has shown for the first time, that magnetic skyrmions can form due to different mechanisms in separate phases in the same material. Their discovery in the chiral magnet Cu2OSeO3 near absolute zero temperature (-273.15 °C) is published in the scientific journal Nature Physics.

Magnetic solitons and topological insulators have “opposite” protected regimes

A cute thought occurred to me today. In the study of magnetic textures, we can have topologically protected spin configurations which belong to nontrivial classes of some homotopy group. Generally speaking, such a configuration assigns a vector on the Bloch sphere to each point in space, m : R² → S², which is equivalent to an endomorphism on S² (by compactifying through the point at infinity). Such a map m, then, is classified by the second homotopy group π2(S²). A [baby] skyrmion belongs to the charge ±1 sector of this group.

Topological protection is so-called because the integral classification of a topological phenomenon cannot be continuously modified by a weak perturbation. What seems to follow: once in a topologically nontrivial sector, always in a topologically nontrivial sector.

But we can of course create and destroy skyrmions in the lab. How is this possible? This question was (mythically) answered by Alexander III of Macedon, namely Alexander the Great, in the fourth century BCE. When faced with the problem of untying the untieable Gordian knot in ancient Phrygia, he famously slashed the knotted rope in half with his sword making him, by a retroactive prophecy, the King of Asia.

Alexander’s key insight was that the topological protection of the Gordian knot could be circumvented by confronting a key assumption: that the rope is a continuous manifold, a prerequisite condition for homotopical classification. At the length scale of a blade’s edge, and the energy scale of human strength, this assumption about rope breaks down, and so Alexander could remove the knot without, strictly speaking, untying it.

This same principle carries over to skyrmions. When the continuum approximation is respected (the Gordian regime), skyrmions are indeed topologically protected. But when sufficiently energetic perturbations occur at small enough length scales (on the order of the lattice constant), the continuum approximation fails to accurately describe our spin system. In this Alexandrian regime, there is no notion of topological protection, and it is here that skyrmions may be created or destroyed.

As promised, I had a cute thought today, and here it is: in a certain sense, the Alexandrian and Gordian take on opposite roles in two main schools of condensed matter topology. I have outlined a bit about spin textures above, which are conserved due to a real space configuration. But the more famous topological insulators are protected by homotopies of the d-torus, which arises as the [crystal] momentum space. In that case, it turns out that the discretization of the lattice is a necessary precondition for nontrivial topology: if the lattice constant were taken to zero, the indices labeling the atomic orbitals would end up being real valued rather than integer valued. Instead of the torus, then, the we would end up with a momentum space given by the Pontryagin dual to the reals---which is just the always uninspiring real numbers themselves, where there are no circles to wind and no homotopy to classify.

Perhaps the inverted role of the continuum approximation in these two cases has something to do with the inverted physical units or the conjugate nature of real and momentum space, but I've not figured it out quite that far quite just yet.

#physics #condensed matter #topological protection #skyrmion #topological insulator #soliton #continuum approximation

“Skyrmions” Could Provide a Way to Bypass the Limits to Moore’s Law

Researchers from MIT show that a newly discovered kind of magnetic behavior holds great promise as a way of storing data — one that could overcome fundamental limits that might otherwise be signaling the end of “Moore’s Law,” which describes the ongoing improvements in computation and data storage over recent decades.

Rather than reading and writing data one bit at a time by changing the orientation of magnetized particles on a surface, as today’s magnetic disks do, the new system would make use of tiny disturbances in magnetic orientation, which have been dubbed “skyrmions.” These virtual particles, which occur on a thin metallic film sandwiched against a film of different metal, can be manipulated and controlled using electric fields, and can store data for long periods without the need for further energy input.

In 2016, a team led by MIT associate professor of materials science and engineering Geoffrey Beach documented the existence of skyrmions, but the particles’ locations on a surface were entirely random. Now, Beach has collaborated with others to demonstrate experimentally for the first time that they can create these particles at will in specific locations, which is the next key requirement for using them in a data storage system. An efficient system for reading that data will also be needed to create a commercializable system.

Researchers make a breakthrough toward the next generation of memory devices

A*STAR and NTU researchers have created a thin film material that allows them to control the size and density of magnetic skyrmions. In addition, they have also achieved electrical detection of these skyrmions. The fabrication process for these films is compatible with current industrial methods. This discovery is a breakthrough and is a key step towards the creation of a skyrmion-based memory device, which is one of the promising contenders for the next generation of memory technologies.

The discovery has been recently published in Nature Materials.

Skyrmions are small particle-like magnetic structures about 400 times smaller than a red blood cell. They can be created in magnetic materials, and their stability at small sizes makes them ideal candidates for memory devices. Since the discovery of room temperature skyrmions in 2015, there has been a global race to create a skyrmion memory device because such a device could potentially hold more information, while using less power.

The need for more memory

Increasingly large amounts of data are created daily in our rapidly digitalised world. Moreover, cutting-edge technologies such as the Internet of Things (IOT), edge computing, and Artificial Intelligence (AI) require immediate processing of this data for effective performance. This requires the development of memory devices with increasingly higher capacities.

Quantum Skyrmions: Helical States In Frustrated Magnets

Skyrmion Revolution: Nanoscale Magnetic Whirls Power Qubits Beyond Limitations An international team of researchers from the Doctoral School at the University of Rzeszów, the Institute of Physics, and I. Javakhishvili Tbilisi State University, including D. Maroulakos, A. Wal, and A. Ugulava, has announced a transformative understanding of quantum skyrmions that will transform quantum information technology. In their latest theoretical study, these tiny magnetic whirls, formerly considered possibilities for quantum bits (qubits), have dramatically increased capabilities as quantum d-level systems, or qudits. This breakthrough increases data capacity and stability of upcoming quantum devices, enabling more powerful and effective quantum computing systems.

Classical Whirls to Quantum Information Powermakers

Skyrmionics studies magnetic topological solitons, or nanoscale magnetic textures—microscopic, stable whirls of magnetism. Over the past decade, this sector has mentioned energy harvesting and eco-friendly nanodevices.

In recent years, quantum skyrmions have emerged with radically distinct properties from classical ones. Quantum skyrmions cannot be characterised by continuous magnetic patterns like classical skyrmions because they are quantum. In triangular spin-frustrated magnets like Gd2PdSi3, conflicting nearest-neighbor (ferromagnetic) and next-nearest-neighbor (antiferromagnetic) interactions cause quantum skyrmion states. Skyrmions in frustrated magnets contain quantum information due to their helical degree of freedom.

The Quantum Leap: Qubits to Qudits

Quantum skyrmions have been studied as two-level qubits by Psaroudaki et al. (2021). The basic unit of quantum information, a qubit, can store one bit. Revolutionary qubit systems are complicated and noise-sensitive. Complex calculations often require many qubits.

This new study proposes a more exact and general analytic solution for weak and arbitrary electric field strengths. This crucial discovery reveals that the system is a skyrmion qudit behind a massive energy barrier, not a qubit. Qudits (d-level quantum systems, d > 2) store more quantum information than qubits. In a d-level qudit, log₂(d) bits of quantum information can be stored. The same amount of information can be stored in fewer qudits than qubits, making quantum circuit topologies more compact and simpler. Qudits' natural depiction of multivalued logic is a major benefit over qubits.

Unmatched Coherence and Strength

High coherence of skyrmion qudits is a major finding. Quantum processes and data integrity require quantum coherence in quantum information theory. Skyrmion quantum qubits have a coherence a thousand times lower than the l₁ norm, according to the team's estimates. This substantially enhanced coherence shows that skyrmion qudits are more durable than qubit states and can tolerate decoherence effects, hardware noise, and ambient noise better. This will help develop stable and reliable quantum information processing systems by directly tackling a major quantum technology development impediment.

Future directions and mathematical rigour

The researchers used group theory, quantum mechanics, and topology to build a mathematical framework to understand these skyrmion qudits' quantum dynamics. The system's evolution is accurately described by a time-dependent Mathieu-Schrödinger equation. The symmetry of this equation was examined by computing level populations and transitions between states using group theoretical analysis. The adiabatic evolution operator developed by M. Berry was used to simulate the drive of quantum states by an external electric field. Qudit nature is enabled by the system's ability to switch energy regimes and populate several quantum states (up to n=7). The adiabatic steering of a strong electric field (estimated at 400 V/m for typical material properties) allows this.

Although assumptions were made, the research notes that minor interactions that were not taken into account would broaden the energy levels, a known phenomenon in spectroscopy. The microsecond coherence duration of these skyrmions allowed unitary dynamics to be considered and relaxation processes to be neglected.

This research has major ramifications for skyrmionics, quantum metrology, and quantum information theory. This major shift from viewing skyrmions as qubits to quits gives up new opportunities for quantum skyrmion-based theory due to their superior coherence and robustness. Twisted nanoscale magnetic whirls may be the key to quantum computing's future by providing a stronger substrate for next-generation quantum devices.

#quantumskyrmions #nanoscalemagneticwhirls #nanoscalemagnetic #Skyrmion #Qudits #Qubits #news #technews #technology #technologynews #govindhtech

Los científicos de la Universidad de Birmingham han logrado crear un modelo experimental de un tipo elusivo de partícula fundamental llamada skyrmion en un haz de luz. El avance proporciona a los fís

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Magnetic vortices as data storage media of the future: Controlled movement of skyrmions

A joint research project being undertaken by Johannes Gutenberg University Mainz (JGU) and the Massachusetts Institute of Technology (MIT) has achieved a breakthrough in fundamental research in the field of potential future data storage technologies. The idea is that electronic storage units (bits) will not be stored on rotating hard disks as is currently standard practice but on a nanowire in the form of magnetic vortex structures, so-called skyrmions, using a process similar to that of a shift register. The magnetic skyrmion bits would be rapidly accessible, while storage density would be high and there would be improved energy efficiency. The project team managed, for the first time, to achieve targeted shifting of individual skyrmions at room temperature using electrical impulses. Their results have been published in the journal Nature Materials.

Magnetic skyrmions are special spin configurations that can occur in materials and particularly in thin layer structures when the inversion symmetry is broken. With regard to the systems that are of interest here, this means that a thin metal film with a non-symmetrical layer structure can be employed. In materials such as this, spin configurations that behave rather like a hair whorl can form. It can be just as difficult to eradicate a skyrmion as it can be to smooth out a hair whorl, a property that gives skyrmions enhanced stability.

Magnetic skyrmions created at room temperature - Could enable a completely unique type of memory

An exotic, swirling object with the sci-fi name of a “magnetic skyrmion” could be the future of nanoelectronics and memory storage. Physicists at UC Davis and the National Institute of Standards and Technology (NIST) have now succeeded in making magnetic skyrmions, formerly found at temperatures close to absolute zero, at room temperature.

“This is a potentially new way to store information, and the energy costs are expected to be extremely low,” said Kai Liu, professor of physics at UC Davis and corresponding author of a paper on the work, published in the journal Nature Communications Oct. 8.

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