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Category: materials

Circa 2016 o,.o.

Titanium is the leading material for artificial knee and hip joints because it’s strong, wear-resistant and nontoxic, but an unexpected discovery by Rice University physicists shows that the gold standard for artificial joints can be improved with the addition of some actual gold.

“It is about 3–4 times harder than most steels,” said Emilia Morosan, the lead scientist on a new study in Science Advances that describes the properties of a 3-to-1 mixture of and gold with a specific atomic structure that imparts hardness. “It’s four times harder than pure titanium, which is what’s currently being used in most dental implants and replacement joints.”

Morosan, a physicist who specializes in the design and synthesis of compounds with exotic electronic and magnetic properties, said the new study is “a first for me in a number of ways. This compound is not difficult to make, and it’s not a new material.”

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Researchers at Utrecht University and at TU Wien (Vienna) create special light waves that can penetrate even opaque materials as if the material was not even there.

Why is sugar not transparent? Because light that penetrates a piece of sugar is scattered, altered and deflected in a highly complicated way. However, as a research team from TU Wien (Vienna) and Utrecht University (Netherlands) has now been able to show, there is a class of very special light waves for which this does not apply: for any specific disordered medium – such as the sugar cube you may just have put in your coffee – tailor-made light beams can be constructed that are practically not changed by this medium, but only attenuated. The light beam penetrates the medium, and a light pattern arrives on the other side that has the same shape as if the medium were not there at all.

This idea of “scattering-invariant modes of light” can also be used to specifically examine the interior of objects. The results have now been published in the journal Nature Photonics.

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This method of finding light patterns that penetrate an object largely undisturbed could also be used for imaging procedures. “In hospitals, X-rays are used to look inside the body—they have a shorter wavelength and can therefore penetrate our skin. But the way a light wave penetrates an object depends not only on the wavelength, but also on the waveform,” says Matthias.

Why is sugar not transparent? Because light that penetrates a piece of sugar is scattered, altered and deflected in a highly complicated way. However, as a research team from TU Wien (Vienna) and Utrecht University (Netherlands) has now been able to show, there is a class of very special light waves for which this does not apply: for any specific disordered medium—such as the sugar cube you may just have put in your coffee—tailor-made light beams can be constructed that are practically not changed by this medium, but only attenuated. The light beam penetrates the medium, and a light pattern arrives on the other side that has the same shape as if the medium were not there at all.

This idea of “scattering-invariant modes of ” can also be used to specifically examine the interior of objects. The results have now been published in the journal Nature Photonics.

An astronomical number of possible wave forms

The waves on a turbulent water surface can take on an infinite number of different shapes—and in a similar way, can also be made in countless different forms. “Each of these light wave patterns is changed and deflected in a very specific way when you send it through a disordered medium,” explains Prof. Stefan Rotter from the Institute of Theoretical Physics at TU Wien.

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Superconductivity – the ability of a material to transmit an electric current without loss – is a quantum effect that, despite years of research, is still limited to very low temperatures. Now a team of scientists at the MPSD has succeeded in creating a metastable state with vanishing electrical resistance in a molecular solid by exposing it to finely tuned pulses of intense laser light. This effect had already been demonstrated in 2016 for only a very short time, but in a new study the authors of the paper have shown a far longer lifetime, nearly 10000 times longer than before. The long lifetimes for light-induced superconductivity hold promise for applications in integrated electronics. The research by Budden et al. has been published in Nature Physics.

Superconductivity is one of the most fascinating and mysterious phenomena of modern physics. It describes the sudden loss of electrical resistance in certain materials when they are cooled below a critical temperature. However, the need for such cooling still limits the technological usability of these materials.

In recent years, research by Andrea Cavalleri’s group at the MPSD has revealed that intense pulses of infrared light are a viable tool to induce superconducting properties in a variety of different materials at much higher temperatures than would be possible without photo-stimulation. However, these exotic states have so far persisted for only a few picoseconds (trillionths of a second), thus limiting the experimental methods for studying them to ultrafast optics.

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Two teams of researchers have independently found that there exists a certain type of graphene system where electrons freeze as the temperature rises. The first team, with members from Israel, the U.S. and Japan, found that placing one layer of graphene atop another and then twisting the one on top resulted in a graphene state in which the electrons would freeze as temperatures rose. And in attempting to explain what they observed, they discovered that the entropy of the near-insulating phase was approximately half of what would be expected from free-electron spins. The second team, with members from the U.S., Japan and Israel, found the same graphene system and in their investigation to understand their observations, they noted that a large magnetic moment arose in the insulator. Both teams have published their results in the journal Nature. Biao Lian with Princeton University has published a News and Views piece outlining the work by both teams in the same journal issue.

As temperatures around most substances rise, the particles they are made of are excited. This results in solids melting to liquids and liquids turning to a gas. This is explained by thermodynamics—higher temperatures lead to more , which is a description of disorder. In this new effort, both teams found an exception to this rule—a graphene system in which electrons freeze as the .

The graphene system was very simple. Both teams simply laid one sheet of on top of another and then twisted the top sheet very slightly. But it had to be twisted at what they describe as the “magic angle,” describing a twist of just 1 degree. The moiré pattern that resulted led to lower velocity of the electrons in the system, which in turn led to more resistance, bringing the system close to being an insulator.

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Researchers have made unparalleled ultrawide-bandgap semiconductors through temperature and timing, just like baking bread.

Alloying, the process of mixing metals in different ratios, has been a known method for creating materials with enhanced properties for thousands of years, ever since copper and tin were combined to form the much harder bronze. Despite its age, this technology remains at the heart of modern electronics and optics industries. Semiconducting alloys, for instance, can be engineered to optimize a device’s electrical, mechanical and optical properties.

Alloys of oxygen with group III elements, such as aluminum, gallium, and indium, are important semiconductor materials with vast applications in high-power electronics, solar-blind photodetectors and transparent devices. The defining property of a semiconductor is its bandgap, a barrier over which only electrons with the required energy can pass. Beta-phase aluminum gallium oxides are notable because of their relatively large bandgap, but most III-O alloys are expensive to make and of unsatisfactory quality.

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Nature’s strongest material now has some stiff competition. For the first time, researchers have hard evidence that human-made hexagonal diamonds are stiffer than the common cubic diamonds found in nature and often used in jewelry.

Named for their six-sided , hexagonal diamonds have been found at some meteorite impact sites, and others have been made briefly in labs, but these were either too small or had too short of an existence to be measured.

Now scientists at Washington State University’s Institute for Shock Physics created hexagonal diamonds large enough to measure their stiffness using . Their findings are detailed in a recent paper in Physical Review B.

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