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Category: materials – Page 12

Electric field tunes vibrations to ease heat transfer

New research from the Department of Energy’s Oak Ridge National Laboratory, in collaboration with The Ohio State University and Amphenol Corporation, challenges conventional understanding about controlling heat flow in solid materials. The study, published in PRX Energy, shows that applying an electric field to a ceramic material changes how phonons (tiny vibrations that carry heat) behave.

Phonons with atoms moving along the field direction (poling direction) last longer than those with atoms moving perpendicular to the field. As a result, the material conducts heat almost three times more efficiently along the field direction than in perpendicular directions. This promising approach could lead to new solid-state devices that control heat flow in everyday technologies.

“Being able to control both how fast and in what manner heat flows could lead to devices that manage thermal energy far more efficiently,” said Puspa Upreti, an ORNL postdoctoral research associate.

Möbius-inspired surface controls light in two directions

Light is an unusually rich carrier of information. Its direction of travel, wavelength, and polarization can all be used to encode signals or images. Yet controlling these properties independently remains difficult, especially when light can enter a device from either side.

In most optical materials—and even in many metasurfaces—the laws of reciprocity and time-reversal symmetry tightly link how a device behaves for forward and backward illumination. As a result, truly different responses in the two directions are hard to achieve in a compact optical element.

The challenge grows sharper when polarization is included. Many metasurfaces work only with simple polarization states, such as horizontal and vertical or left-and right-circular polarization.

How “Empty Space” Is Supercharging Atomically Thin Semiconductors

A single layer of atoms may seem too thin to meaningfully interact with light, yet materials like tungsten disulfide are reshaping what is possible in nanophotonics. Researchers have now found a way to dramatically strengthen these interactions. Atomically thin semiconductors such as tungsten dis

Hidden atomic dichotomy drives superconductivity in ultra-thin compound

Physicists in China have unveiled new clues to the origins of high-temperature superconductivity in an iron-based material just a single unit-cell thick. Led by Qi-Kun Xue and Lili Wang at Tsinghua University, the team’s experiments show that the effect emerges through a striking dichotomy between two atomic “sublattices” in the material—offering deeper insight into how superconductivity arises. Their results are published in Physical Review Letters.

When cooled below its critical temperature, a superconductor allows electrical currents to flow with virtually zero resistance. While most superconductors discovered so far have critical temperatures close to absolute zero, recent decades have seen the discovery of increasingly advanced materials that host the effect at ever higher temperatures, making them far easier to implement for practical applications.

In 2012, superconductivity was discovered in a single-unit-cell-thick layer of iron selenide (FeSe), consisting of a Se–Fe–Se trilayer only 0.55 nm thick. However, it remained unclear how such a strong superconducting effect could emerge in such an ultrathin system.

Liquid crystal phase in antiferromagnets can be detected electrically

The best candidate for next-generation magnetic devices—technology that can power, store, sense or transport information—may be, counterintuitively, antiferromagnets. Today, the most widely used magnetic materials are ferromagnets, which exhibit permanent magnetization and therefore strongly attract each other. Their opposite, called antiferromagnetic materials, exhibit no net magnetization at all. Despite a net zero magnetic field, they offer appealing properties that would solve the challenges of current magnetic technologies, like stray magnetic field generation or slow operation.

Now, a team led by researchers at Tohoku University has taken the first step toward developing antiferromagnetic technology. The researchers found, for the first time, that under a current, antiferromagnets can exhibit a phase of matter known as “liquid-crystal,” or nematic, that can be electrically detected. Their study is published in Nature Communications.

“The antiferromagnets we work with possess a fundamentally different symmetry from conventional ferromagnets, meaning that they are not simply an alternative material platform, but a new class of magnets expected to host entirely new electronic functionalities,” said corresponding author Hideaki Sakai.

Letting atomic simulations learn from phase diagrams

A new computational method allows modern atomic models to learn from experimental thermodynamic data, according to a University of Michigan Engineering and Université Paris-Saclay study published in Nature Communications. Leveraging a machine learning technique called score matching, the method expresses the thermodynamic free energy of atomic systems as a function of the underlying atomic interaction model, unlike standard schemes where the interaction model is fixed.

By returning thermodynamic predictions as functions rather than static numbers, the method, which is also over 10 times more efficient than previous approaches, can easily quantify and help accelerate computational materials discovery by opening up new inverse design capabilities. The method is called “descriptor density of states” and is abbreviated D-DOS.

“The D-DOS method provides a two-way connection between the latest generation of atomic simulations and the classical resource of phase diagrams, exposing these datasets to machine learning-driven computer models,” said Thomas Swinburne, an assistant professor of mechanical engineering at U-M and co-corresponding author of the study.

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