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Category: particle physics – Page 7

Light pulses uncover Higgs mode that reshapes perovskite crystal symmetry

Waves of light and sound interact to drive electronic and structural changes in a perovskite crystal. At the atomic scale, nothing is ever truly still. Materials that appear perfectly rigid and motionless to the naked eye are in fact swarms of vibrating atoms. This motion is generally random and uncoordinated, but with the right input, the atoms in certain materials will start to move together, vibrating in sync.

These collective vibrations are a form of sound called phonons, and when tuned just right, they can influence a material’s structure and behavior in dramatic and useful ways. Researchers are working to understand and control this effect to optimize material properties and even access hidden phases of matter.

Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory are using light to drive phonon activity in a class of materials called metal halide perovskites, whose customizable structures and photosensitivity hold promise for use in next-generation solar cells, advanced sensors and quantum information technologies.

The delusion of a particle-only universe

If everything that happens in the world ultimately comes down to the behavior of fundamental particles, it would seem that other entities, from cells to human beings, from currencies to financial markets, aren’t really causing anything at all—that they are just shadows cast by patterns at the most fundamental level. But philosopher David Yates argues this conclusion is wrong. The whole affects the parts, and higher-level structures don’t just describe what is happening at lower levels in more convenient terms—they actively shape what is possible. This means that chemists, biologists, psychologists, and economists aren’t chasing shadows. They are studying structures that genuinely shape how the world unfolds.

In 1974, Jerry Fodor published a seminal paper titled ‘Special Sciences’, in which he argued for an intuitive and compelling picture of the relationship between fundamental physics and higher-level sciences such as biology, psychology and economics. Our world, according to Fodor, is arranged hierarchically, with fundamental physical particles at the bottom, combining to form molecules, which combine to form cells, which combine to form complex organisms, some of which have mental states, among them humans, who combine to form complex societies. The sciences are likewise arranged, with physics at the bottom, followed by chemistry, biology, physiology, neuroscience, psychology, sociology and economics. Now it is vanishingly unlikely, says Fodor, that things that share e.g. psychological or economic properties, also share some property specifiable in the language of physics or other lower-level sciences.

Quantum shell structure reveals new rule for proton-neutron pairing inside nuclei

Nuclear physicists used a little magic in their latest experiment conducted at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility, and the result has revealed surprising new information about the behavior of protons and neutrons inside the atom’s nucleus. Specifically, the research revealed another requirement that determines how protons and neutrons pair up.

The result is reported in the journal Nature.

The research involves short-range correlations (SRCs). This phenomenon describes when a proton and a neutron, or two protons or two neutrons, briefly pair up inside the nucleus.

Water-wave tweezers steer tiny ‘surfers’ without touching them

Summer brings with it the sight of surfers moving seamlessly across wave crests, with ocean waters carrying them along coastlines. A team of scientists has now created a similar phenomenon—with small objects rather than surfers—that can be controlled by humans rather than by nature.

Through a series of experiments on a replicated mini-beach, NYU researchers show how water waves can be used to move floating objects or hold them firmly in place—all without direct touch or contact.

“Our study shows how beaming water waves at a floating object can cause it to move sideways or be ‘tweezed’ and held precisely in place,” explains Leif Ristroph, a professor at New York University’s Courant Institute School of Mathematics, Computing, and Data Science and the senior author of the study, which appears in the journal Physical Review Fluids. “These surprising effects could be used to manipulate particles and structures, controlling their motions and positions.”

Cutting a photon in two creates an infinite swarm of particles

By definition, elementary particles can’t be broken into smaller pieces. But in a new theoretical study published in Physical Review Letters, Johannes Skaar and colleagues have revealed what would happen if you tried anyway for a single photon. The answer is deeply strange: attempting to cut a photon in two wouldn’t produce two smaller photons, but instead conjure an infinite number of them out of thin air.

Like any quantum particle, a photon exists simultaneously as a single, localized particle, and an extended wave, spread out across space. For their investigation, Skaar’s team considered what would happen if a single photon passed through an optical shutter—essentially a very fast mirror that can be switched on and off to block part of a pulse of light. If the shutter was fast enough, it could intercept the photon mid-pulse, snipping off part of this extended wave.

To find out what would happen afterward, the researchers applied quantum equations that describe how the photon’s underlying electromagnetic field behaves at the quantum level. Specifically, their analysis tracked precisely how the photon’s quantum state would be transformed by the shutter’s intervention.

Molecular glasses solve long-standing Arrhenius paradox

Glasses are non-crystalline but solid states of matter in which molecules and atoms are not arranged into a regular crystal lattice, but rather in a disordered pattern. Glassy materials are widely used in various settings, for instance, in the synthesis of pharmaceuticals and the development of electronics or optical devices.

When studying movement and changes in various materials and substances, physicists commonly rely on the so-called Arrhenius model. This is a mathematical framework introduced by Svante Arrhenius in 1889, which can be used to calculate how temperature affects the speed of a heat-activated chemical reaction or physical process.

Past studies have shown that when the Arrhenius model is applied to molecular glasses, it yields unrealistically small pre-exponential factors. Pre-exponential factors are values that describe the intrinsic timescale of the movement of molecules without considering temperature effects.

Atomic reshuffle leads to record-breaking catalysts for hydrogen production

Researchers have discovered that atoms can be mixed, separated, and recombined within the same experiment, providing a pathway to a record-breaking catalyst for green hydrogen production. In their study, the team created nanoscale particles containing only a few dozen platinum and nickel atoms and observed unusual dynamic behavior in direct space and in real time. As the two metals separate from one another while maintaining an interface, they become highly active for electrochemical water splitting, leading to efficient hydrogen evolution.

The project was led by the University of Nottingham in collaboration with the University of Birmingham, Diamond Light Source, and Ulm University in Germany. The study appears in Advanced Materials.

Research team leader Dr. Jesum Alves Fernandes, from the School of Chemistry, University of Nottingham, said, “What makes this discovery exciting is that we can reversibly tune the structure of the particle while directly observing the process at the atomic scale. This opens a new strategy for designing adaptive catalysts for a wide range of applications.”

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