A new tool can determine whether a collection of building blocks will assemble into a mechanically sound structure.
Category: materials – Page 153
In 1911, physicist Heike Kamerlingh Onnes used liquid helium—whose production method he invented—to cool mercury to a few kelvins, discovering that its electrical resistance dropped to nil. Although mercury was later found to be a “conventional” superconductor, no microscopic theory so far managed to fully explain the metal’s behavior and to predict its critical temperature TC. Now, 111 years after Kamerlingh Onnes’ discovery, theorists have done just that. Their first-principles calculations accurately predict mercury’s TC but also pinpoint theoretical caveats that could inform searches for room-temperature superconductors [1].
Mercury is an exception among conventional superconductors, most of which can be successfully described with state-of-the-art density-functional-theory methods. To tackle mercury’s unique challenges, Gianni Profeta of the University of L’Aquila, Italy, and colleagues scrutinized all physical properties relevant for conventional superconductivity, which is mediated by the coupling of electrons to phonons. In particular, the researchers accounted for previously neglected relativistic effects that alter phonon frequencies, they improved the description of electron-correlation effects that modify electronic bands, and they showed that mercury’s d-electrons provide an anomalous screening effect that promotes superconductivity by reducing Coulomb repulsion between superconducting electrons. With these improvements, their calculations delivered a TC prediction for mercury only 2.5% lower than the experimental value.
The new understanding of the oldest superconductor will find a place in textbooks but may also offer valuable lessons for superconductivity research, says Profeta. A promising material-by-design approach involves “high-throughput” computations that screen millions of theoretical material combinations to suggest those that could be conventional superconductors close to ambient conditions. “If we don’t include subtle effects similar to those relevant for mercury, these computations may overlook many interesting materials or err in their critical temperature predictions by hundreds of kelvins,” he says.
Sisti was able to further develop the design after joining Studio MOM, testing a wide range of material compositions to find the most effective solution.
The various elements of the helmet are combined during the process. This allows the mycelium to bond with the hemp textile that forms the strap and outer skin, providing extra support and removing the need for glue.
Studio MOM has carried out a series of initial tests to ensure the product’s safety for use.
When we encounter metals in our day-to-day lives, we perceive them as shiny. That’s because common metallic materials are reflective at visible light wavelengths and will bounce back any light that strikes them. While metals are well suited to conducting electricity and heat, they aren’t typically thought of as a means to conduct light.
But in the burgeoning field of quantum materials, researchers are increasingly finding examples that challenge expectations about how things should behave. In new research published in Science Advances, a team led by Dmitri Basov, Higgins Professor of Physics at Columbia University, describes a metal capable of conducting light. “These results defy our daily experiences and common conceptions,” said Basov.
The work was led by Yinming Shao, now a postdoc at Columbia who transferred as a Ph.D. student when Basov moved his lab from the University of California San Diego to New York in 2016. While working with the Basov group, Shao has been exploring the optical properties of a semimetal material known as ZrSiSe. In 2020 in Nature Physics, Shao and his colleagues showed that ZrSiSe shares electronic similarities with graphene, the first so-called Dirac material discovered in 2004. ZrSiSe, however, has enhanced electronic correlations that are rare for Dirac semimetals.
face_with_colon_three circa 2020.
Exploiting two-dimensional metamaterials, the direction of emission from InGaN/GaN quantum wells is engineered while simultaneously improving quantum efficiency.
New research finds evidence of waveguiding in a unique quantum material. These findings counter expectations about how metals conduct light and may push imaging beyond optical diffraction limits.
We perceive metals as shiny when we encounter metals in our day-to-day lives. That’s because common metallic materials are reflective at visible light wavelengths and will therefore bounce back the light that strikes them. Although metals are well suited to conducting electricity and heat, they aren’t typically thought of as a means to conduct light.
However, scientists are increasingly finding examples that challenge expectations about how things should behave in the burgeoning field of quantum materials. New research describes a metal capable of conducting light through it. Conducted by a team of researchers led by Dmitri Basov, Higgins Professor of Physics at Columbia University.
Circa 2021 face_with_colon_three
New technique reclaims nearly 100% of all-carbon-based transistors while retaining future functionality of the materials.
Strange metals, or non-Fermi liquids, are distinct states of matter that have been observed in different quantum materials, including cuprate superconductors. These states are characterized by unusual conductive properties, such as a resistivity that is linearly associated with temperature (T-linear).
In the strange metal phase of matter, electrons undergo what is known as “Planckian dissipation,” a high scattering rate that linearly increases as the temperature rises. This T-linear, strong electron scattering is anomalous for metals, which typically present a quadratic temperature dependence (T2), as predicted by the standard theory of metals.
Researchers at Université de Sherbrooke in Canada, Laboratoire National des Champs Magnétiques Intenses in France, and other institutes worldwide have recently carried out a study exploring the possibility that the resistivity of strange metals is not only associated with temperature, but also with an applied magnetic field. This magnetic field linearity had been previously observed in some cuprates and pnictides, with some physicists suggesting that it could also be linked to Planckian dissipation.
A ring-shaped waveguide with a particular pattern of notches can force a light wave to make two round trips before completing an integer number of wave cycles.
Light can travel along a closed path inside a ring of glass or similar material, reflecting repeatedly from the interior surface. Although such closed-loop waves generally have integer values of angular momentum, researchers using a small gear-shaped ring have now demonstrated an ability to generate similar waves with unusual fractional values of angular momentum [1]. As in a Möbius strip, the waves must make two round trips to return to their initial configuration. The ability to tune the angular momentum in this way could give researchers more precise control of light in advanced devices such as single-photon emitters.
Physicists refer to the closed-loop waves as whispering gallery modes, named after an acoustic effect in round rooms, where sounds reflect multiple times off the walls. Ordinarily, a wave of this kind moves around a single closed loop before retracing its earlier path. The phase of the electric field associated with the wave front must go through an integer number M of cycles in making one loop. Technically, this condition also implies that the photons associated with the wave will carry an integer number M units of angular momentum.
Researchers find that a phenomenon called multifractality manifests in the conductance fluctuations of a 2D electron gas as the gas undergoes a topological phase transition.
Fractals are geometric patterns that repeat themselves across different length scales. Such patterns are ubiquitous, appearing in the outlines of snowflakes, in swirls of turbulent fluids, and in graphs tracing the highs and lows of financial markets. Now Aveek Bid and his colleagues at the Indian Institute of Science in Bangalore show that fractals can also emerge in the electrical-conductance fluctuations of a 2D electron gas in graphene as the electron gas transitions between two topological phases [1]. The results confirm predictions made earlier this year [2].
Subject a 2D electron gas to a strong perpendicular magnetic field, and its Hall conductance—the conductance perpendicular to an induced current—takes on certain discrete values. But during a transition from one discrete value to another, this conductance can exhibit fluctuations. Bid and his colleagues measured these fluctuations in the 2D electron gases of two graphene-based devices. Using detailed data analysis, they determined that the conductance fluctuations contained patterns that could be accurately described by a multifractal—a fractal that scales spatially in several different ways.