Symplectic geometry is a relatively new field with implications for much of modern mathematics. Here’s what it’s all about.
Forty-five years after superconductivity was first discovered in metals, the physics giving rise to it was finally explained in 1957 at the University of Illinois at Urbana-Champaign, in the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity.
Thirty years after that benchmark achievement, a new mystery confronted condensed matter physicists: the discovery in 1987 of copper-oxide or high-temperature superconductors. Now commonly known as the cuprates, this new class of materials demonstrated physics that fell squarely outside of BCS theory. The cuprates are insulators at room temperature, but transition to a superconducting phase at a much higher critical temperature than traditional BCS superconductors. (The cuprates’ critical temperature can be as high as 170 Kelvin—that’s −153.67°F—as opposed to the much lower critical temperature of 4 Kelvin—or −452.47°F—for mercury, a BCS superconductor.)
The discovery of high-temperature superconductors, now more than 30 years ago, seemed to promise that a host of new technologies were on the horizon. After all, the cuprates’ superconducting phase can be reached using liquid nitrogen as a coolant, instead of the far costlier and rare liquid helium required to cool BCS superconductors. But until the unusual and unexpected superconducting behavior of these insulators can be theoretically explained, that promise remains largely unfulfilled.
The possibility of achieving room temperature superconductivity took a tiny step forward with a recent discovery by a team of Penn State physicists and materials scientists.
The surprising discovery involved layering a two-dimensional material called molybdenum sulfide with another material called molybdenum carbide. Molybdenum carbide is a known superconductor—electrons can flow through the material without any resistance. Even the best of metals, such as silver or copper, lose energy through heat. This loss makes long-distance transmission of electricity more costly.
“Superconductivity occurs at very low temperatures, close to absolute zero or 0 Kelvin,” said Mauricio Terrones, corresponding author on a paper in Proceedings of the National Academy of Sciences published this week. “The alpha phase of Moly carbide is superconducting at 4 Kelvin.”
It is a widely accepted theory today that when the first stars formed in our universe approximately 13 billion years ago, they quickly came together to form globular clusters. These clusters then coalesced to others to form the first galaxies, which have been growing through mergers and evolving ever since. For this reason, astronomers have long suspected that the oldest stars in the universe are to be found in globular clusters.
The study of stars in these clusters is therefore a means of determining the age of the universe, which is still subject to some guesswork. In this vein, an international team of astronomers and cosmologists recently conducted a study of globular clusters in order to infer the age of the universe. Their results indicate that the universe is about 13.35 billion years old, a result that could help astronomers learn more about the expansion of the cosmos.
Their study, titled “Inferring the Age of the Universe with Globular Clusters,” recently appeared online and was submitted for consideration to the Journal of Cosmology and Astroparticle Physics. The study was led by David Valcin, a predoctoral researcher from the Institute of Cosmos Sciences at the University of Barcelona (ICCUB), who was joined by a team from France, Spain, and the US.
As we welcome wireless technology into more areas of life, the additional electronic bustle is making for an electromagnetically noisy neighborhood. In hopes of limiting the extra traffic, researchers at Drexel University have been testing two-dimensional materials known for their interference-blocking abilities. Their latest discovery, reported in the journal Science, is of the exceptional shielding ability of a new two-dimensional material that can absorb electromagnetic interference rather than just deflecting back into the fray.
The material, called titanium carbonitride, is part of a family of two-dimensional materials, called MXenes, that were first produced at Drexel in 2011. Researchers have revealed that these materials have a number of exceptional properties, including impressive strength, high electrical conductivity and molecular filtration abilities. Titanium carbonitride’s exceptional trait is that it can block and absorb electromagnetic interference more effectively than any known material, including the metal foils currently used in most electronic devices.
“This discovery breaks all the barriers that existed in the electromagnetic shielding field. It not only reveals a shielding material that works better than copper, but it also shows an exciting, new physics emerging, as we see discrete two-dimensional materials interact with electromagnetic radiation in a different way than bulk metals,” said Yury Gogotsi, Ph.D., Distinguished University and Bach professor in Drexel’s College of Engineering, who led the research group that made this MXene discovery, which also included scientists from the Korea Institute of Science and Technology, and students from Drexel’s co-op partnership with the Institute.
A team of researchers from the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS) has just announced that they managed to calculate how to create matter and antimatter using lasers.
This means that, by focusing high-powered laser pulses, we might soon be able to create matter and antimatter using light.
To break this down a bit, light is made of high-energy photons. When high-energy photons go through strong electric fields, they lose enough radiation that they become gamma rays and create electron-positron pairs, thus creating a new state of matter.
Tailoring and manipulating electromagnetic wave propagation has been of great interest within the scientific community for many decades. In this context, wave propagation has been engineered by properly introducing spatial inhomogeneities along the path where the wave is traveling. Antennas and communications systems in general have greatly benefited from this wave-matter control. For instance, if one needs to re-direct the radiated field (information) from an antenna (transmitter) to a desired direction and reach a receiving antenna placed at a different location, one can simply place the former in a translation stage and mechanically steer the propagation of the emitted electromagnetic wave.
Such beam steering techniques have greatly contributed to the spatial aiming of targets in applications such as radars and point-to-point communication systems. Beam steering can also be achieved using metamaterials and metasurfaces by means of spatially controlling the effective electromagnetic parameters of a designed meta-lens antenna system and/or using reconfigurable meta-surfaces. The next question to ask: Could we push the limits of current beam steering applications by controlling electromagnetic properties of media not only in space but also in time (i.e., 4D metamaterials x, y,z, t)? In order words, would it be possible to achieve temporal aiming of electromagnetic waves?
In a new paper published in Light Science & Applications, Victor Pacheco-Peña from the School of Mathematics, Statistics and Physics of Newcastle University in UK and Nader Engheta from and Department of Electrical and Systems Engineering of the University of Pennsylvania, USA have answered this question by proposing the idea of temporal metamaterials that change from an isotropic to an anisotropic permittivity tensor. In this concept, the authors consider a rapid change of the permittivity of the whole medium where the wave is traveling and demonstrated both numerically and analytically the effects of such a temporal boundary caused by the rapid temporal change of permittivity. In so doing, forward and backward waves are produced with wave vector k preserved through the whole process while frequency is changed, depending on the values of the permittivity tensor before and after the temporal change of permittivity.
Researchers from Kazan Federal University, Texas A&M University and Institute of Applied Physics (Russian Academy of Sciences) found ways to direct high frequency gamma radiation by means of acoustics.
Their paper describes an optical ‘switch’—a device able to let through or stop gamma quanta by switching the acoustic field. Basically, the mechanism makes iron ‘transparent’ for gamma rays when needed.
The Mossbauer Spectroscopy Lab of Kazan Federal University showed acoustically induced transparency of a resonant medium for gamma radiation in an experiment. The essence of this phenomenon lies in the transformation of the spectrum of the absorption line into a comb structure consisting of satellite lines spaced from the main line by the frequency of the acoustic field. For the experiment, gamma quanta with an energy of 14.4 keV were used, which are emitted during the decay of the excited state of the iron-57 nucleus.
