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Orbital currents are the lesser-known cousins of spin currents. Both involve an alignment of angular momentum. But spin currents are carried by spin-polarized electrons, while orbital currents are carried by electrons in orbitals having the same angular momentum. Like their spin counterparts, orbital currents could be useful for transmitting information in so-called orbitronic devices, but researchers had expected that these currents would not travel well across material interfaces. Now Igor Lyalin and Roland Kawakami from Ohio State University have measured the flow of orbital currents across selected materials placed in multilayer structures. They find, surprisingly, that the transport of orbital currents is as good or better than the transport of spin currents for most of the sampled materials.
Orbital currents can be generated via the so-called orbital Hall effect—a surface magnetization effect that was predicted 20 years ago but directly detected only in 2023 (see Synopsis: Detection of the Orbital Hall Effect). Interest in orbital currents is growing, as they could be more effective than spin currents at switching the orientation of magnetic layers in data-storage devices.
To study orbital current transport, Lyalin and Kawakami fabricated structures consisting of chromium and nickel layers, separated by a thin spacer. For the spacer material, they tested nonmagnetic metals, ferromagnetic metals, and antiferromagnetic insulators. The researchers generated an orbital current by applying a voltage to the chromium layer, and they measured how much of this current flowed through the structures by observing a magnetization change in the nickel. They found that 12 of the 15 spacer materials transported orbital currents more efficiently than spin currents—a result that could be good news for developing future orbitronic devices, Kawakami says.
A 25-qubit quantum processor architecture reduces the stray signals that can cause errors and is suitable for scaling up.
Imaging Antiferromagnetic Domains
Posted in materials
A simple light microscopy setup can map the micrometer-scale domains of a potentially useful class of magnetic materials.
Ultraviolet photons induce potassium niobate to behave like a potent solid-state refrigerant, according to new calculations.
Claudio Cazorla of the Polytechnic University of Catalonia in Spain and his collaborators have used a suite of numerical methods to discover that the archetypal ferroelectric material, potassium niobate (KNO), also exhibits a photocaloric effect: In response to ultraviolet light, KNO reversibly absorbs heat [1]. Because the effect is large and works at a wide range of temperatures, including room temperature, KNO could serve as the working medium for new cooling devices.
KNO owes its ferroelectric and photocaloric effects to its perovskite crystal structure, which features a niobium ion surrounded by an octahedral cage of oxygen ions. At low temperatures, the niobium ion is offset from the cage’s center, which induces an electric polarization (the ferroelectric effect). Above 700 K, KNO adopts a nonpolar configuration as its most stable phase.
Several fields of mathematics have developed in total isolation, using their own “undecipherable” coded languages. In a new study published in Proceedings of the National Academy of Sciences, Tamás Hausel, professor of mathematics at the Institute of Science and Technology Austria (ISTA), presents “big algebras,” a two-way mathematical ‘dictionary’ between symmetry, algebra, and geometry, that could strengthen the connection between the distant worlds of quantum physics and number theory.
A nationwide analysis of community-level floodplain development found that over two-million acres of floodplain were developed over the past two decades across the United States, with roughly half of all new floodplain housing built in Florida.
The interactions between quantum spins underlie some of the universe’s most interesting phenomena, such as superconductors and magnets. However, physicists have difficulty engineering controllable systems in the lab that replicate these interactions.
A small black hole must work harder against gravity to keep from collapsing. In rapidly rotating black holes, the Ni shell would collapse to a torus, as possibly reflected in the dramatic photos of supermassive black holes.
At a deeper level, the gravity/Λ mechanism might be seen as a kind of quantum overlay of the Ni solutions, a possible step towards reconciliation of the quantum gravity and general relativity perspectives.
Cosmologists will not be quick to endorse a shell universe. There is still much heavy lifting still to do, for instance, in matching the Ni solutions to the observed universe. Dark matter and dark energy will not lightly be cast aside. But if I am right, the universe is not as you may always have thought.
Researchers from Monash University, part of the FLEET Center, have revealed a generic approach towards intrinsic magnetic second-order topological insulators. These materials are crucial for advancements in spintronics, an emerging field aiming at using spin degree of freedom to deliver information. Their study is published in Nano Letters.