A research team has successfully visualized the ultrafast dynamics of quasi-particles known as excitons, which are generated in carbon nanotubes (CNTs) upon light excitation.
Category: particle physics – Page 4
Dramatic stretch in quantum materials confirms 100-year-old prediction
Research from the University of St Andrews has set a new benchmark for the precision with which researchers can explore fundamental physics in quantum materials. The work has implications extending from materials science to advanced computing, as well as confirming a nearly 100-year-old prediction.
The researchers explored magnetoelastic coupling, which is the change in the size or shape of a material when exposed to a magnetic field. It is usually a small effect, but one that has technological consequences.
A team from the School of Physics and Astronomy at the University of St Andrews has now discovered that this effect is remarkably large in a case where one wouldn’t have expected it—in a transition metal oxide. Oxides are a chemical compound containing at least one oxygen atom and one other element in its chemical formula. High-temperature superconductors are one of the most prominent examples of a transition metal oxide.
Astronomers are Closing in on the Source of Galactic Cosmic Rays
In 1912, astronomer Victor Hess discovered strange, high-energy particles known as “cosmic rays.” Since then, researchers have hunted for their birthplaces. Today, we know about some of the cosmic ray “launch pads”, ranging from the Sun and supernova explosions to black holes and distant active galactic nuclei. What astronomers are now searching for are sources of cosmic rays within the Milky Way Galaxy.
In a pair of presentations at the recent American Astronomical Society meeting, a team led by Michigan State University’s Zhuo Zhang, proposed an interesting place where cosmic rays originate: a pulsar wind nebula in our own Milky Way Galaxy. A pulsar is a rapidly rotating neutron star, formed as a result of a supernova explosion. High-energy particles and the neutron star’s strong magnetic field combine to interact with the nearby interstellar medium. The result is a pulsar wind nebula that can be detected across nearly the whole electromagnetic spectrum, particularly in X-rays. It makes sense that this object would be a source of cosmic rays. Pulsars are found throughout the Galaxy, which makes them a useful category in the search for cosmic ray engines in the Milky Way.
The Vela Pulsar is a good example of a pulsar wind nebula. The pulsar is at the center, and the surrounding cloudiness is the nebula. Courtesy NASA.
New Material Breaks the Rules: Scientists Turn Insulator Into a Semiconductor
Once considered merely insulating, a change in the angle between silicon and oxygen atoms opens a pathway for electrical charge to flow.
A breakthrough discovery from the University of Michigan has revealed that a new form of silicone can act as a semiconductor. This finding challenges the long-held belief that silicones are only insulating materials.
“The material opens up the opportunity for new types of flat panel displays, flexible photovoltaics, wearable sensors or even clothing that can display different patterns or images,” said Richard Laine, U-M professor of materials science and engineering and macromolecular science and engineering and corresponding author of the study recently published in Macromolecular Rapid Communications.
Crystal melting and the glass transition obey the same physical law
The melting of crystals is the process by which an increase in temperature induces the disruption of the ordered crystalline lattice, leading to the disordered structure and highly fluctuating dynamic behavior of liquids. At the glass transition, where an amorphous solid (a glass) turns into a liquid, there is no obvious change in structure, and only the dynamics of the atoms change, going from strongly localized dynamics in space (in the glass state) to the highly fluctuating (diffusive) dynamics in the liquid.
The search for the atomic-scale mechanism of 3D crystal melting has a long history in physics, and famous physicists such as Max Born, Neville Mott and Frederick Lindemann proposed different ways to look at it. I have always had the impression that we still do not understand the melting of 3D crystals, which is a highly complicated cooperative process involving nonlinearly coupled dynamics of a huge number of atoms. This complexity I always found very fascinating.
Comparatively, the melting of 2D solids, mediated by dislocations-unbinding, is much better understood, and the theory that describes it led to the 2017 Nobel prize in physics for Kosterlitz and Thouless.
Simulation reveals emergence of jet from binary neutron star merger followed by black hole formation
Binary neutron star mergers, cosmic collisions between two very dense stellar remnants made up predominantly of neutrons, have been the topic of numerous astrophysics studies due to their fascinating underlying physics and their possible cosmological outcomes. Most previous studies aimed at simulating and better understanding these events relied on computational methods designed to solve Einstein’s equations of general relativity under extreme conditions, such as those that would be present during neutron star mergers.
Researchers at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Yukawa Institute for Theoretical Physics, Chiba University, and Toho University recently performed the longest simulation of binary neutron star mergers to date, utilizing a framework for modeling the interactions between magnetic fields, high-density matter and neutrinos, known as the neutrino-radiation magnetohydrodynamics (MHD) framework.
Their simulation, outlined in Physical Review Letters, reveals the emergence of a magnetically dominated jet from the merger, followed by the collapse of the binary neutron star system into a black hole.
A Fifth Force of Nature May Have Been Discovered Inside Atoms
Every action in physics is governed by some kind of push or pull. As far as we know, these all fall into one of just four categories; electromagnetism, gravity, and two kinds of nuclear force.
Yet there could well be forces hidden deep within the tiny storms of particle dynamics that have been simply too subtle to easily detect.
Physicists from Germany, Switzerland, and Australia have now placed new restrictions on where one example of a ‘fifth’ force may be hiding in the hearts of atoms, exchanging whispers between electrons and neutrons.
Physicists record the most precise neutrino mass measurement ever
The Standard Model of particle physics, our best guide to the building blocks of nature, once claimed neutrinos were massless. But that turned out to be wrong. Neutrinos do have mass—just an incredibly tiny one. So far, though, no experiment has measured that mass directly. That’s where the KATRIN experiment comes in.
KATRIN stands for the Karlsruhe Tritium Neutrino Experiment. It’s based in Germany and stretches nearly 70 meters, or about 230 feet—longer than a Boeing 747. Published in the journal, Science, the experiment uses a radioactive form of hydrogen called tritium, which naturally decays into helium. When this happens, it releases an electron and a neutrino.
By measuring the energy of the electron, scientists can figure out how much energy the neutrino took away. This helps them estimate the neutrino’s mass. The trick is, this has to be done with extreme accuracy. That’s why KATRIN includes one of the world’s most advanced spectrometers, which is 10 meters wide and filters out unwanted particles with precision.
Semi-heavy water ice detected around young sunlike star for first time
A team led by astronomers at Leiden University in the Netherlands and the National Radio Astronomy Observatory in Virginia (U.S.) have, for the first time, robustly detected semi-heavy water ice around a young sunlike star. The results strengthen the case that some of the water in our solar system formed before our sun and the planets.
Their findings are published in The Astrophysical Journal Letters.
One way that astronomers trace the origin of water is through measuring its deuteration ratio. That is the fraction of water that contains one deuterium atom instead of one of the hydrogens. So instead of H2O, it’s HDO, which is also called semi-heavy water. A high fraction of semi-heavy water is a sign that the water formed in a very cold place, such as the primitive dark clouds of dust, ice, and gas from which stars are born.