Phys.org April 26, 2023 Time metamaterials offer a great potential for wave manipulation. Researchers at the City University of New York explored the exotic wave dynamics of an anisotropic photonic time crystal (APTC) formed by an anisotropic medium whose optical properties are uniformly and periodically changed in time. Based on a temporal transfer matrix formalism, they showed that a stationary charge embedded in an APTC emits radiation, in contrast to the case of isotropic photonic time crystals, and its distribution in momentum space is controlled by the APTC band structure. According to the researchers their approach greatly extends the concept […]
Category Archives: Materials science
Improving alloys: Researchers successfully establish a strong mechanical bond of immiscible iron and magnesium
Phys.org April 17, 2023 Steel is heavy, and scientists are turning to alternatives in the quest to improve the safety and speed of transportation, while simultaneously lessening its environmental footprint. Joining of Mg alloy to steel has received wide attention for design of multi-materials. Researchers in Japan have described joining of immiscible pure iron and pure magnesium (Fe–Mg), as a simplified model, performed by solid metal dealloying (SMD) between Mg and Fe100−xNix interlayers that were preliminary joined to the Fe part by diffusion bonding. SMD formed an Fe–Mg bicontinuous composite with interconnected morphology at the Fe–Mg weld interface. The effect […]
Scientists use computational modeling to design “ultrastable” materials
MIT News April 4, 2023 High-throughput screening of hypothetical metal-organic framework databases can uncover new materials, but their stability in real-world applications is often unknown. Researchers at MIT leveraged community knowledge and machine learning models to identify MOFs that are thermally stable and stable upon activation. They separated the MOFs into their building blocks and recombined them to make a new hypothetical MOF database of over 50,000 structures with orders of magnitude more connectivity nets and inorganic building blocks than were present in prior databases. This database showed a 10-fold enrichment of ultrastable MOF structures that were stable upon activation […]
Experiment unlocks bizarre properties of strange metals
Science Daily March 13, 2023 An iternational team of researchers (Japan, USA – University of Cincinnati, Rutgers University) fired gamma rays at an alloy of ytterbium to observe its unusual electrical behavior. They studied the charge fluctuations of the strange metal phase of β-YbAlB4 as a function of temperature and pressure they found that the usual single absorption peak in the Fermi-liquid regime splits into two peaks upon entering the critical regime. The team interpreted this spectrum as a single nuclear transition, modulated by nearby electronic valence fluctuations whose long time scales are further enhanced by the formation of charged […]
Magnetism fosters unusual electronic order in quantum material
Phys.org March 13, 2023 Various correlated electronic phases have been discovered in kagome lattice materials, including magnetism, charge density waves, nematicity and superconductivity. Recently, a charge density wave was discovered in the magnetic kagome FeGe, providing a platform for understanding the interplay between charge order and magnetism in kagome materials. An internationl team of researchers (USA – Rice University, UC Berkeley, University of Washington, University, SLAC National Acclerator Laboratory, Oak Ridge National Laboratory, Lawrence Berkeley Laboratory, Israel, China) observed all three electronic signatures of the kagome lattice in FeGe using angle-resolved photoemission spectroscopy. They showed that the presence of van […]
Smooth sailing for electrons in graphene: Measuring fluid-like flow at nanometer resolution
Phys.org February 16, 2023 Electron flow in conductors becomes viscous when electron-electron collisions dominate over collisions with defects and other sources of resistance. An international team of researchers (USA – University of Wisconsin, Japan) investigated such behavior by using scanning tunneling potentiometry to probe the nanometer-scale flow of electron fluids in graphene as they pass through channels defined by smooth and tunable in-plane p-n junction barriers. They observed that as the sample temperature and channel widths were increased, the electron fluid flow underwent a Knudsen-to-Gurzhi transition from the ballistic to the viscous regime characterized by a channel conductance that exceeded […]
Elusive transition shows universal quantum signatures
Phys.org February 14, 2023 Recent experiments in moiré transition metal dichalcogenide materials have reported the observation of a continuous bandwidth-tuned transition from a metal to a paramagnetic Mott insulator at a fixed filling of one electron per moiré unit cell. The electrical transport measurements reveal several puzzling features that are seemingly at odds with the theoretical expectations of an interaction-induced, but disorder-free, bandwidth-tuned metal-insulator transition. A team of researchers in the US (Cornell University, MIT) included the effects of long-wavelength inhomogeneities, building on the results for a continuous metal-insulator transition at fixed filling in the clean limit. They examined the […]
Researchers find thermal limits of advanced nanomaterials
Phys.org February 15, 2023 Boron nitride nanotubes (BNNTs), structural analogues to carbon nanotubes, are a strong candidate for nanofillers in high-temperature composites due to their high thermal stability, oxidation resistance, excellent mechanical properties, and high thermal conductivity. A team of researchers in the US (FAMU-FSU College of Engineering, industry) tested samples of high-quality, high-purity BNNTs in an inert atmosphere for thermal failure up to 2500 °C. A significant fraction of the BNNTs survived temperatures as high as 2200°, and the BNNT samples were completely undamaged at temperatures as high as 1800 °C. Boron nitride (BN) nanopowders were tested identically to […]
New crystal growth orientation method manipulates properties of materials
Phys.org February 8, 2023 Single crystalline materials have the potential to exhibit superior performance because they exclude grain boundaries, which increase susceptibility to creep, oxidation, and corrosion, and make thermal and electronic transport inefficient. However, single crystal properties vary significantly with crystallographic orientation, making the ability to control the orientation critical for their use in applications. The complex nature of crystal nucleation and growth processes makes such control challenging. A team of researchers in the US (Texas A&M University, University of Virginia, Argonne National Laboratory) has developed a new crystal reorientation mechanism that results in abrupt and massive orientation changes […]
Organic semiconductors curl up in the dark
Nanowerk January 17, 2023 Organic semiconductors have the potential to replace their silicon predecessors in many applications. However, the manufacturing processes of solar cells that achieve such efficiencies are not yet compatible with mass production. An international team of researchers (Denmark, Germany) used roll-to-roll methos to print the organic semiconductor (poly(3-hexylthiophene) or P3HT), used for flexible solar cells, and organic electronics directly on a polymer film. In solution without illumination or under red light, the polymer chains quickly aggregated and formed ordered domains. When illuminated under green or blue light, the more rigid polymer chains, excited by the light, were […]