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A collaborative study conducted by Prof. Zhao Jin, Associate Prof. Zheng Qijing from the University of Science and Technology of China (USTC), and Prof. Hrvoje Petek from the University of Pittsburgh, has revealed the mechanisms behind the transition of bright-dark excitons in anatase TiO₂. Their findings have been published in Proceedings of the National Academy of Sciences.

Understanding Excitons

Excitons, quasi-particles formed by the binding of electrons and holes in condensed matter systems via Coulomb interaction, exhibit distinct properties as bright and dark excitons. While bright excitons directly couple with light and play a pivotal role in light absorption, dark excitons, with their relatively longer lifetimes, hold significance in quantum information processing, Bose-Einstein condensation, and light-energy harvesting.

Directing magnetization with a low electric field is crucial for advancing effective spintronic devices. In spintronics, the characteristics of an electron’s spin or magnetic moment are leveraged for information storage. By modifying orbital magnetic moments through strain, it’s possible to manipulate electron spins, leading to an enhanced magnetoelectric effect for superior performance.

Japanese researchers, including Jun Okabayashi from the University of Tokyo, revealed a strain-induced orbital control mechanism in interfacial multiferroics. In multiferroic material, the magnetic property can be controlled using an electric field—potentially leading to efficient spintronic devices. The interfacial multiferroics that Okabayashi and his colleagues studied consist of a junction between a ferromagnetic material and a piezoelectric material. The direction of magnetization in the material could be controlled by applying voltage.

Recent research has discovered that, in contrast to earlier assumptions, substantial quantities of aerosol particles are generated across extensive regions of the West Siberian taiga during spring. These findings indicate that rising temperatures can greatly influence the climate due to this phenomenon.

Aerosol particles significantly contribute to the Earth’s cooling process. They can impact the amount of sunlight that reaches the Earth’s surface either directly or indirectly by aiding in cloud formation. These particles originate from various gas molecules and are found all over the planet.

To understand the circumstances in which these particles are formed, researchers conduct measurements in various environments all over the world. For example, the Finnish flagship station SMEAR II has conducted measurements in the boreal forest for 25 years.

While atomic clocks are already the most precise timekeeping devices in the universe, physicists are working hard to improve their accuracy even further. One way is by leveraging spin-squeezed states in clock atoms.

Spin-squeezed states are entangled states in which particles in the system conspire to cancel their intrinsic quantum noise. These states, therefore, offer great opportunities for quantum-enhanced metrology since they allow for more precise measurements. Yet, spin-squeezed states in the desired optical transitions with little outside noise have been hard to prepare and maintain.

One particular way to generate a spin-squeezed state, or squeezing, is by placing the clock atoms into an optical cavity, a set of mirrors where light can bounce back and forth many times. In the cavity, atoms can synchronize their photon emissions and emit a burst of light far brighter than from any one atom alone, a phenomenon referred to as superradiance. Depending on how superradiance is used, it can lead to entanglement, or alternatively, it can instead disrupt the desired quantum state.

Electronics are based on electrical charges being transported from one place to another. Electrons move, current flows, and signals are transmitted by applying an electrical voltage. However, there is also another way to manipulate electronic currents and signals: using the properties of the spin—the intrinsic magnetic moment of the electron. This is called “spintronics,” and it has become an increasingly important field in contemporary electronic research.

An international research team involving TU Wien and the Czech Academy of Sciences has now achieved an important breakthrough. They have managed to switch the spins in an antiferromagnetic material using surface strain. This could lead to an important new line of research in electronic technologies. The research is published in the journal Advanced Functional Materials.

“There are different types of magnetism,” explains Sergii Khmelevskyi from the Vienna Scientific Cluster Research Center, TU Wien. “The best known is ferromagnetism. It occurs when the atomic spins in a material are all aligned in parallel. But there is also the opposite, antiferromagnetism. In an antiferromagnetic material, neighboring atoms always have opposite spins.” Their effects therefore cancel each other out and no magnetic force can be detected from the outside.

Does dark matter reside in a deformed mirror universe of our own, where rules are different and atoms failed to form?

A team of physicists, including University of Massachusetts assistant professor Tigran Sedrakyan, recently announced in the journal Nature that they have discovered a new phase of matter. Called the “chiral Bose-liquid state,” the discovery opens a new path in the age-old effort to understand the nature of the physical world.

Under everyday conditions, matter can be a solid, liquid or gas. But once you venture beyond the everyday—into temperatures approaching absolute zero, things smaller than a fraction of an atom or which have extremely low states of energy—the world looks very different. “You find quantum states of matter way out on these fringes,” says Sedrakyan, “and they are much wilder than the three classical states we encounter in our everyday lives.”

Sedrakyan has spent years exploring these wild quantum states, and he is particularly interested in the possibility of what physicists call “band degeneracy,” “moat bands” or “kinetic frustration” in strongly interacting quantum matter.

The quantum ground state of an acoustic wave of a certain frequency can be reached by completely cooling the system. In this way, the number of quantum particles, the so-called acoustic phonons, which cause disturbance to quantum measurements, can be reduced to almost zero and the gap between classical and quantum mechanics bridged.

Over the past decade, major technological advances have been made, making it possible to put a wide variety of systems into this state. Mechanical vibrations oscillating between two mirrors in a resonator can be cooled to very low temperatures as far as the quantum ground state. This has not yet been possible for optical fibers in which high-frequency sound waves can propagate. Now researchers from the Stiller Research Group have taken a step closer to this goal.

A joint research project of Johannes Gutenberg University Mainz (JGU), the University of Siegen, Forschungszentrum Jülich, and the Elettra Synchrotron Trieste has achieved a new milestone for the ultra-fast control of magnetism. The international team has been working on magnetization configurations that exhibit chiral twisting. Chirality is a symmetry breaking, which occurs, for example, in nature in molecules that are essential for life. Chirality is also referred to as handedness, since hands are an everyday example of two items that—arranged in a mirror-inverted manner—cannot be superimposed onto each other. Magnetization configurations with a fixed chirality are currently investigated intensively due to their fascinating properties such as enhanced stability and efficient manipulation by current. These magnetic textures thus promise applications in the field of ultrafast chiral spintronics, for example in ultrafast writing and controlling of chiral topological magnetic objects such as magnetic skyrmions, i.e., specially twisted magnetization configurations with exciting properties.

The new insights published in Nature Communications shed light on the ultrafast dynamics after optical excitation of chiral spin structures compared to collinear spin structures. According to the researchers’ findings, the chiral order restores faster compared to the collinear order after excitation by an infrared laser.

The research team performed small angle X-ray scattering experiments on magnetic thin film samples stabilizing chiral magnetic configurations at the free electron laser (FEL) facility FERMI in Trieste in Italy. The facility provides the unique possibility to study the magnetization dynamics with femtosecond time resolution by using circular left polarized or right polarized light. The results indicate a faster recovery of chiral order compared to collinear magnetic order dynamics, which means that twists are more stable than straight magnetic configurations.