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Category: particle physics

Controlling exciton flow in moiré superlattices: New method leverages correlated electrons

Excitons are pairs of bound negatively charged electrons and positively charged holes that form in semiconductors, enabling the transport of energy in electronic devices. These pairs of charge carriers also emerge in transition metal dichalcogenides, thin semiconducting materials comprised of a transition metal and two chalcogen atoms.

Researchers at Carnegie Mellon University, UC Riverside, and other institutes have introduced a new strategy to control the flow of energy in structures comprised of two transition metal dichalcogenide layers stacked with a small rotational mismatch, also known as moiré superlattices.

Their proposed approach, introduced in a paper published in Nature Communications, entails the active tuning of electronic states in moiré superlattices in ways that alter the transport of excitons.

Cosmic knots may finally explain why the Universe exists

Knotted structures once imagined by Lord Kelvin may actually have shaped the universe’s earliest moments, according to new research showing how two powerful symmetries could have created stable “cosmic knots” after the Big Bang. These exotic objects may have briefly dominated the young cosmos, unraveled through quantum tunneling, and produced heavy right-handed neutrinos whose decays tipped the balance toward matter over antimatter.

In 1867, Lord Kelvin pictured atoms as tiny knots in an invisible medium called the ether. That picture turned out to be wrong, since atoms are built from subatomic particles rather than twists in space. Yet his discarded idea of knotted structures may still help explain one of the deepest questions in science: why anything in the universe exists at all.

A team of physicists in Japan has now shown that knotted structures can naturally appear in a realistic particle physics model that also addresses several major mysteries, including the origins of neutrino masses, dark matter, and the strong CP problem. Their study, published in Physical Review Letters, suggests that such “cosmic knots” could have formed in the violently changing early universe, briefly taken over as a dominant form of energy, and then collapsed in a way that slightly favored matter over antimatter. As they formed and decayed, these knots would have stirred spacetime itself, producing a distinctive pattern of gravitational waves that future detectors might be able to pick up, which is rare for a problem that is usually very difficult to test directly.

Turning plastic waste into valuable chemicals with single-atom catalysts

The rapid accumulation of plastic waste is currently posing significant risks for both human health and the environment on Earth. A possible solution to this problem would be to recycle plastic waste, breaking it into smaller molecules that can be used to produce valuable chemicals.

Researchers at Nanjing Forestry University and Tsinghua University recently introduced a new approach to convert polystyrene (PS), a plastic widely used to pack some foods and other products, into toluene, a hydrocarbon that is of value in industrial and manufacturing settings. Their proposed strategy, outlined in a paper published in Nature Nanotechnology, entails heating polystyrene waste in hydrogen and breaking it down into smaller vapor molecules, a process known as hydro-pyrolysis.

Life-cycle and techno-economic analyses performed by the team showed that the newly introduced process could reduce the carbon footprint of toluene production by 53%, producing toluene at an estimated cost of $0.61/kg, which is below the current industry benchmark.

Where’s my qubit? Scientists develop technique to detect atom loss

Quiet quitting isn’t just for burned out employees. Atoms carrying information inside quantum computers, known as qubits, sometimes vanish silently from their posts. This problematic phenomenon, called atom loss, corrupts data and spoils calculations.

But Sandia National Laboratories and the University of New Mexico have for the first time demonstrated a practical way to detect these “leakage errors” for neutral atom platforms. This achievement removes a major roadblock for one branch of quantum computing, bringing scientists closer to realizing the technology’s full potential. Many experts believe quantum computers will help reveal truths about the universe that are impossible to glean with current technology.

“We can now detect the loss of an atom without disturbing its ,” said Yuan-Yu Jau, Sandia atomic physicist and principal investigator of the experiment team.

Physicists found a way to see heat in empty space

Physicists have found a clever way to detect the elusive Unruh effect without extreme accelerations. By using atoms that emit light cooperatively between mirrors, acceleration subtly shifts when a powerful light burst appears. That early flash acts like a timestamped signature of the effect. The method could make once-theoretical physics experimentally reachable.

A cryogenic winter for tomorrow’s accelerator

Behind every particle collision generated at the Large Hadron Collider is a multitude of technical feats. One of these is refrigeration on an industrial scale. To guide the particles, the thousands of superconducting magnets in the accelerator must be cooled to a temperature of close to absolute zero. This makes the LHC the largest cryogenic installation in the world: 23 of its 27 kilometers are maintained at 1.9 Kelvin (−271°C) using refrigerators in which superfluid helium circulates.

This unique cooling system needs to be further strengthened in preparation for the High-Luminosity LHC (HL-LHC), a major upgrade to the LHC that is scheduled to begin operation in 2030. On both sides of the two large experiments, ATLAS and CMS, more powerful focusing magnets and new types of cavities will considerably increase the number of collisions at each beam crossing or, in other words, the luminosity. This ultra-sophisticated equipment requires increased cooling power. Two new refrigerators are therefore being installed, in addition to the eight that are already needed for the existing accelerator.

The LHC’s refrigerators work on the same principle as the one in your kitchen, except that they are gigantic installations that occupy several buildings. Located on the surface, they include large compressors and an enormous cold box that contains the heat exchangers and the expansion turbines. These installations lower the helium temperature to 4.5 Kelvin (−268.6°C). Six compression units were installed in October.

A Long-Standing Spintronics Mystery May Finally Be Solved

A long-standing explanation for magnetoresistance may be incomplete. New evidence suggests a universal interfacial mechanism is at play. A major advance in spintronics came with the discovery of unusual magnetoresistance (UMR). In this effect, the electrical resistance of a heavy metal changes wh

Private donors pledge $1 billion for world’s largest particle accelerator

Europe’s physics lab CERN on Thursday said private donors had pledged $1 billion toward the construction of a new particle accelerator that would be by far the world’s biggest.

In a first, private individuals and philanthropic foundations have backed a flagship research project at CERN, the European Organization for Nuclear Research, which seeks to unravel what the universe is made of and how it works.

The donors include the Breakthrough Prize Foundation of billionaire Silicon Valley investor Yuri Milner; the Eric and Wendy Schmidt Fund for Strategic Innovation of former Google chief executive Eric Schmidt; plus Italian Agnelli family heir John Elkann, and French telecoms tycoon Xavier Niel.

Archimedean screw inspires new way to encode chirality into magnetic materials

In physics and materials science, the term “spin chirality” refers to an asymmetry in the arrangement of spins (i.e., the intrinsic angular momentum of particles) in magnetic materials. This asymmetry can give rise to unique electronic and magnetic behaviors that are desirable for the development of spintronics, devices that leverage the spin of electrons and electric charge to process or store information.

The creation of materials that exhibit desired spin chirality and associated physical effects on a large scale has so far proved challenging. In a recent paper published in Nature Nanotechnology, researchers at École Polytechnique Fédérale de Lausanne (EPFL), the Max Planck Institute for Chemical Physics of Solids and other institutes introduced a new approach to encode chirality directly into materials by engineering their geometry at a nanoscale.

“Dirk and myself were initially inspired by the elegance of the Archimedean screw and began wondering whether we could build a magnonic analog, something that could ‘pump’ magnons (i.e., collective electron spin excitations) in a similarly directional way,” Dr. Mingran Xu, first author of the paper, told Tech Xplore.

Physicists bring unruly molecules to the quantum party

Scientists have made leaps and bounds in bending atoms to their will, making them into everything from ultraprecise clocks to bits of quantum data. Translating these quantum technologies from obedient atoms to unruly molecules could offer greater possibilities. Molecules can rotate and vibrate. That makes molecules more sensitive to certain changes in the environment, like temperature.

“If you’re sensitive to something, it can be a curse, because you would like to not be sensitive, or it can be a blessing,” said NIST physicist Dietrich Leibfried. “You can use that sensitivity to your advantage.”

But that same sensitivity has made molecules difficult to control. Recently, physicists at the National Institute of Standards and Technology (NIST) achieved new levels of control over molecules. In a study published in Physical Review Letters, they were able to manipulate a calcium hydride molecular ion—made up of one atom of hydrogen and one atom of calcium, with one electron removed to make it a charged molecule—with almost perfect success. And this control opens possibilities for quantum technology, chemical research and exploring new physics.

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