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February 26th, 2013

Other materials stories that may be of interest

Published on February 26th, 2013 | By: Eileen De Guire

Some other stories and papers worth looking into:

Coupling the valley degree of freedom to antiferromagnetic order

(PNAS) The exploration of novel electronic degrees of freedom has important implications in both basic quantum physics and advanced information technology. Valley, as a new electronic degree of freedom, has received considerable attention in recent years. In this paper, we develop the theory of spin and valley physics of an antiferromagnetic honeycomb lattice. We show that by coupling the valley degree of freedom to antiferromagnetic order, there is an emergent electronic degree of freedom characterized by the product of spin and valley indices, which leads to spin-valley-dependent optical selection rule and Berry curvature-induced topological quantum transport. These properties will enable optical polarization in the spin-valley space, and electrical detection/manipulation through the induced spin, valley, and charge fluxes. The domain walls of an antiferromagnetic honeycomb lattice harbors valley-protected edge states that support spin-dependent transport. Finally, we use first-principles calculations to show that the proposed optoelectronic properties may be realized in antiferromagnetic manganese chalcogenophosphates (MnPX3, X=S, Se) in monolayer form.

Force is key to granular state-shifting

Physicists have explored the changing behavior of granular materials by comparing it to what happens in thermodynamic systems. In a thermodynamic system, you can change the state of a material—like water—from a liquid to a gas by adding energy (heat) to the system. One of the most fundamental and important observations about temperature, however, is that it has the ability to equilibrate. Physicists thought they could use thermodynamics’ underlying ideas to explain the changes in granular materials, but didn’t know whether granular materials had properties which might equilibrate in a similar way. In other words, instead of temperature being the change agent in a granular system, it might be a property related to the amount of free space, or the forces on the particles. But no one had really tested which of the two might exhibit equilibration. NC State physicist Karen Daniels and former graduate student James Puckett devised a way to do just that. “Physicists often have ideas that are theoretically elegant, such as the idea that there might be new temperature-like variables to be discovered, and then it’s exciting to go into the lab and see how well these ideas work in practice,” says Daniels. “In this case, we found it is possible to take the temperature of a granular system and find out more about what makes it change its state. The ‘thermometer’ for this temperature is actually the particles themselves,” says Puckett.

A tantalising prospect: Exotic but useful metals such as tantalum and titanium are about to become cheap and plentiful

(Economist) Aluminum was once more costly than gold. How times change. And in aluminium’s case they changed because, in the late 1880s, Charles Hall and Paul Héroult worked out how to separate the stuff from its oxide using electricity. Now, the founders of Metalysis, a small British firm, hope to do much the same with tantalum, titanium and a host of other recherché and expensive metallic elements including neodymium, tungsten and vanadium. The effect could be profound. Tantalum is an ingredient of the best electronic capacitors. At the moment it is so expensive ($500-2,000 a kilogram) that it is worth using only in things where size and weight matter a lot, such as mobile phones. Drop that price and it could be deployed more widely. Neodymium is used in the magnets of motors in electric cars. Vanadium and tungsten give strength to steel, but at great expense. And the strength, lightness, high melting point and ability to resist corrosion of titanium make it an ideal material for building aircraft parts, supercars and medical implants-but it can cost 50 times as much as steel. Guppy Dhariwal, Metalysis’s boss, thinks however that the company can make titanium powder (the product of its new process) for less than a tenth of such powder’s current price. The Hall-Héroult method requires both input oxide and output metal to be in liquid form. That demands heat. The Metalysis trick is to do the electrolysis on powdered oxides directly, without melting them. The company’s first product is tantalum. Its factory is not much bigger than a house, but has enough capacity to supply 3-4 percent of the 2,500 tons of this metal that are used around the world each year. The resulting income, the firm hopes, will provide it with the grubstake it needs to move on to the big prize: titanium.

The future of 3D printing: University of Virginia expert weighs in

President Obama highlighted 3D printing in his recent State of the Union address, calling it the technology that “has the potential to revolutionize the way we make almost everything.” Increasingly, with user-friendly computer programs and 3D printers, the designer can be anybody. Eventually, almost any object or parts for objects, may become 3D printable, including body implants, in a range of materials, including medals. Engineers and engineering students at the University of Virginia are using sophisticated 3D printing technology to make an array of objects, including a plastic airplane for an Army project. David Sheffler, a U.Va. professor of mechanical and aerospace engineering in the School of Engineering and Applied Science and 20-year veteran of the aerospace industry, teaches 3D printing to engineering students and, in this Q&A, discusses the future of 3D printing in industry and society.

How “Bullet Time” will revolutionize exascale computing

(MIT Technology Review) The exascale computing era is almost upon us and computer scientists are already running into difficulties. 1 exaflop is 10^18 floating point operations per second, that’s a thousand petaflops. The current trajectory of computer science should produce this kind of capability by 2018 or so. The problem is not processing or storing this amount of data-Moore’s law should take care of all that. Instead, the difficulty is uniquely human. How do humans access and make sense of the exascale data sets? In a nutshell, the problem is that human senses have a limited bandwidth-our brains can receive information from the external world at roughly gigabit rates. So a computer simulation at exascale data rates simply overwhelms us. The answer, of course, is to find some way to compress the output data without losing its essential features. Today, Akira Kageyama and Tomoki Yamada from Kobe University in Japan put forward a creative solution. These guys say the trick is to use “bullet time”, the Hollywood filming technique made famous by movies like The Matrix. Their idea is to surround the simulated action with thousands, or even millions, of virtual cameras that all record the action as it occurs. Humans can later “fly” through the action by switching from one camera angle to the next, just like bullet time.

Vienna University of Technology researchers show that a recently discovered class of materials can be used to create a new kind of solar cell

Single atomic layers are combined to create novel materials with completely new properties. Layered oxide heterostructures are a new class of materials, which has attracted a great deal of attention among materials scientists in the last few years. A research team at the Vienna University of Technology (TUW), together with colleagues from the US and Germany, has now shown that these heterostructures can be used to create a new kind of extremely efficient ultrathin solar cells. “Single atomic layers of different oxides are stacked, creating a material with electronic properties which are vastly different from the properties the individual oxides have on their own”, says Karsten Held, a professor at TUW’s Institute for Solid State Physics. In order to design new materials with exactly the right physical properties, the structures were studied in large-scale computer simulation, and they discovered that the oxide heterostructures hold great potential for building solar cells. “The crucial advantage of the new material is that on a microscopic scale, there is an electric field inside the material, which separates electrons and holes,” says Elias Assmann, who carried out a major part of the computer simulations. The oxides used to create the material are actually isolators. However, if two appropriate types of isolators are stacked, an astonishing effect can be observed: the surfaces of the material become metallic and conduct electrical current. “For us, this is very important. This effect allows us to conveniently extract the charge carriers and create an electrical circuit,” says Held.



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One Response to Other materials stories that may be of interest

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