Researchers have investigated how pores in a solid change its chemical reactions with other materials. The result could make steel production more environmentally friendly.
Graphene is found to exhibit a magnetoresistance dwarfing that of all known materials at room temperature—a behavior that may lead to new magnetic sensors and help decipher the physics of strange metals.
One might expect that, two decades after its discovery, graphene would have exhausted its potential for surprises. But the thinnest, strongest, most conductive of all materials has now added another record to its tally. A collaboration that includes graphene’s codiscoverer and Nobel laureate Andre Geim of the University of Manchester, UK, reports that graphene can have a room-temperature magnetoresistance—a magnetic-field-induced change in electrical resistivity—that’s 100 times larger than that of any known material [1]. Graphene’s giant magnetoresistance could lead to novel magnetic-field sensors but also offer an experimental window into exotic quantum regimes of electrical conduction that might be related to the mysterious “strange metals.”
Magnetoresistance, which occurs both in bulk materials and multilayer structures, found a killer app in magnetic-field sensors such as those used to read data from magnetic memories. Researchers have long been interested in the limits of this phenomenon, which has led to discoveries of “giant,” “colossal,” and “extraordinary” forms of magnetoresistance. The associated materials exhibit resistivity changes of up to 1,000,000% when exposed to magnetic fields of several teslas (T). The largest effects, however, require extremely low temperatures that can only be reached with impractical liquid-helium cooling systems.
After amazing us with its incredible strength, flexibility and thermal conductivity, graphene has now chalked up another remarkable property with its magnetoresistance. Researchers in Singapore and the UK have shown that, in near-pristine monolayer graphene, the room-temperature magnetoresistance can be orders of magnitude higher than in any other material. It could therefore provide both a platform for exploring exotic physics and potentially a tool for improving electronic devices.
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Magnetoresistance is a change in electrical resistance on exposure to a magnetic field. In the classical regime, magnetoresistance arises because the magnetic field curves the trajectories of flowing charges by the Lorentz force. In traditional metals, in which conduction occurs almost solely through electron motion, magnetoresistance quickly saturates as the field increases because the deflection of the electrons creates a net potential difference across the material, which counteracts the Lorentz potential. The situation is different in semimetals such as bismuth and graphite, in which current is carried equally by electrons and positive holes. Opposite charges flowing in opposite directions end up being deflected the same way by the magnetic field, so no net potential difference is generated and the magnetoresistance can theoretically grow indefinitely.
RIKEN physicists have created an exotic quantum state in a device with a disk-like geometry for the first time, showing that edges are not required. This demonstration opens the way for realizing other novel electronic behavior. Their findings are published in Nature Physics.
Physics has long moved on from the three classic states of matter: solid, liquid and gas. A better theoretical understanding of quantum effects in crystals and the development of advanced experimental tools to probe and measure them has revealed a whole host of exotic states of matter.
A prominent example of this is the topological insulator: a kind of crystalline solid that exhibits wildly different properties on their surfaces than in the rest of the material. The best-known manifestation of this is that topological insulators conduct electricity on their surfaces but are insulating in their interiors.
A fluid flow called a vortex ring can effectively remove oil from a thin, porous material and can clean both surfaces at once.
Physicists and material scientists have been trying to metallize hydrogen for many decades, but they have not yet succeeded. In 1968, British physicist Neil Ashcroft predicted that atomic metallic hydrogen would be a high-temperature semiconductor.
Most recent studies also suggested that this elusive and hypothetical form of hydrogen would also conduct electricity with no resistance when its temperature exceeds that of boiling water. This prediction ultimately paved the way for the discovery of high-temperature superconductivity in hydrides (i.e., compounds containing hydrogen and a metal).
Researchers at Sapienza University of Rome, Sorbonne University, CNRS, and the International School for Advanced Studies (SISSA) have recently carried out a study aimed at thoroughly characterizing the behavior and properties of hydrogen at high pressures. Their paper, published in Nature Physics, outlines a highly accurate phase diagram of high-pressure hydrogen, which could inform ongoing efforts aimed at creating atomic metallic hydrogen.
Two-dimensional (2D) magnetic insulators, which are electrically insulating materials with long-range magnetic order, could be used to fabricate compact magneto-electric or magneto-optical devices. Efficiently and reliably controlling the properties of these atomically thin magnets through electrical means, however, has so far proved to be highly challenging, as the materials’ charge levels often cannot be largely adjusted and their crystal fields cannot be considerably altered using external electric fields.
Researchers at University of Maryland and their collaborators recently devised a new strategy that could be used to efficiently control 2D magnetic insulators. This strategy, outlined in a paper in Nature Electronics, relies on the use of a thin ferroelectric polymer that can modulate the 2D materials’ magnetic responses.
“When it comes to electronic devices, people are primarily pursuing a smaller form factor (relating to higher integration density, which means more devices can be integrated on the unit area/volume of a chip), lower energy consumption, and higher performance,” Cheng Gong, the lead principal investigator for the study, told Tech Xplore.
Scientists have discovered yet another amazing aspect of the weird and wonderful behavior of water—this time when subjected to nanoscale confinement at sub-zero temperatures.
The finding that a crystalline substance can readily give up water at temperatures as low as −70 °C, published in the journal Nature on April 12, has major implications for the development of materials designed to extract water from the atmosphere.
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The protoplanet was found surrounding HD 169,142, a star located 374 light years from our solar system.
Astronomers have caught a rare glimpse of a planet’s formation. This is only the third time scientists have discovered a protoplanet — an early stage in forming a planet, where cosmic material clumps in a disk surrounding newborn stars.
The observation of new protoplanet.
Continue reading “Astronomers confirm presence of third protoplanet about 374 light years away” »
