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Category: particle physics – Page 279

Over the past few decades, physicists and engineers have been trying to create increasingly compact laser-plasma accelerators, a technology to study matter and particle interactions produced by interactions between ultrafast laser beams and plasma. These systems are a promising alternative to existing large-scale machines based on radio-frequency signals, as they can be far more efficient in accelerating charged particles.

While laser-plasma accelerators are not yet widely employed, several studies have highlighted their value and potential. To optimize the quality of the accelerated laser beam produced by these devices, however, researchers will need to be able to monitor several ultra-fast physical processes in real-time.

Researchers at the Weizmann Institute of Science (WIS) in Israel have recently devised a method to directly observe laser-driven and nonlinear relativistic plasma waves in real-time. Using this method, introduced in a paper published in Nature Physics, they were able to characterize nonlinear plasma at incredibly high temporal and spatial resolutions.

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Strong alternating magnetic fields can be used to generate a new type of spin wave that was previously just theoretically predicted. This was achieved for the first time by a team of physicists from Martin Luther University Halle-Wittenberg (MLU). They report on their work in Nature Communications and provide the first microscopic images of these spin waves.

The basic idea of spintronics is to use a special property of electrons—spin—for various electronic applications such as data and . The spin is the intrinsic angular momentum of electrons that produces a magnetic moment. Coupling these magnetic moments creates the magnetism that could ultimately be used in . When these coupled are locally excited by a pulse, this dynamic can spread like waves throughout the material. These are referred to as spin waves or magnons.

A special type of those waves is at the heart of the work of the physicists from Halle. Normally, the non-linear excitation of magnons produces integers of the output frequency—1,000 megahertz becomes 2,000 or 3,000, for example.

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Physicists have discovered a material in which atoms are arranged in a way that so frustrates the movement of electrons that they engage in a collective dance where their electronic and magnetic natures appear to both compete and cooperate in unexpected ways.

Led by Rice University physicists, the research was published online today in Nature. In experiments at Rice, Oak Ridge National Laboratory (ORNL), SLAC National Accelerator Laboratory, Lawrence Berkeley National Laboratory (LBNL), the University of Washington (UW), Princeton University and the University of California, Berkeley, researchers studied pure iron-germanium crystals and discovered standing waves of fluid electrons appeared spontaneously within the crystals when they were cooled to a critically low temperature. Intriguingly, the arose while the material was in a , to which it had transitioned at a higher temperature.

“A charge wave typically occurs in materials that have no magnetism,” said study co-corresponding author Pengcheng Dai of Rice. “Materials that have both a charge density wave and magnetism are actually rare. Even more rare are those where the charge density wave and magnetism ‘talk’ to each other, as they appear to be doing in this case.”

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The discovery of the Higgs boson ten years ago in the Large Hadron Collider was the culmination of decades of work and the collaboration of 1000s of brilliant and passionate people. It was the final piece needed to confirm the standard model of particle physics as it now stands. There are still many outstanding questions — for example, it seems like nothing in the standard model can explain what dark matter is. So the discovery of the Higgs wasn’t the end of particle physics — but it may be the way forward. Many physicists think that the secret to finding the elusive dark matter particle will come by studying the Higgs. In fact, the first tantalizing evidence is already in.

Continue reading “Could the Higgs Boson Lead Us to Dark Matter?” | >

New research reveals that spinning quasiparticles, or magnons, light up when paired with a light-emitting quasiparticle, or exciton, with potential quantum information applications.

All magnets contain spinning quasiparticles called magnons. This is true of all magnets from the simple souvenirs hanging on your refrigerator to the discs that give your computer memory storage to the powerful versions used in research labs. The direction one magnon spins can influence that of its neighbor, which in turn affects the spin of its neighbor, and so on, yielding what are known as spin waves. Spin waves can potentially transmit information more efficiently than electricity, and magnons can serve as “quantum interconnects” that “glue” quantum bits together into powerful computers.

Although magnons have enormous potential, they are often difficult to detect without bulky pieces of lab equipment. According to Columbia researcher Xiaoyang Zhu, such setups are fine for conducting experiments, but not for developing devices, such as magnonic devices and so-called spintronics. However, seeing magnons can be made much simpler with the right material: a magnetic semiconductor called chromium sulfide bromide (CrSBr) that can be peeled into atom.

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Few things in the Universe keep the beat as reliably as an atom’s pulse.

Yet even the most advanced ‘atomic’ clocks based on variations of these quantum timekeepers lose count when pushed to their limits.

Physicists have known for some time that entangling atoms can help tie particles down enough to squeeze a little more tick from every tock, yet most experiments have only been able to demonstrate this on the smallest of scales.

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Not everything needs to be seen to be believed; certain things are more readily heard, like a train approaching its station. In a recent paper, published in Physical Review Letters, researchers have put their ears to the rail, discovering a new property of scattering amplitudes based on their study of sound waves through solid matter.

Be it light or sound, physicists consider the likelihood of particle interactions (yes, sound can behave like a particle) in terms of probability curves or scattering amplitudes. It is common lore that when the momentum or energy of one of the scattered particles goes to zero, scattering amplitudes should always scale with integer powers of momentum (i.e., p1, p2, p3, etc.). What the research team found however, was that the can be proportional to a fractional power (i.e., p1/2, p1/3, p1/4, etc.).

Why does this matter? While quantum field theories, such as the Standard Model, allow researchers to make predictions about particle interactions with extreme accuracy, it is still possible to improve upon current foundations of fundamental physics. When a new behavior is demonstrated—such as fractional-power scaling—scientists are given an opportunity to revisit or revise existing theories.

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A matter-wave interferometer can probe the magnetism of a broad range of species, from single atoms to very large, weakly magnetic molecules.

This year marks the centenary of the ground-breaking experiment of Otto Stern and Walther Gerlach that demonstrated the quantization of the spin angular momentum of an atom [1]. The evidence came from the observation that a beam of silver atoms, upon traversing a spatially varying magnetic field, split into two beams. The spatial splitting of the spin-up and spin-down atoms corresponded to an atomic magnetic moment of 1 Bohr magneton—the magnetic moment of a single spinning electron. The deflection of particle beams in a spatially varying magnetic field remains the basis of techniques for characterizing the magnetic properties of isolated atoms and molecules. Such techniques, however, aren’t sufficiently sensitive to study very large, weakly magnetic molecules, including many biological molecules.

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Topological materials that possess certain atomic-level symmetries, including topological insulators and topological semi-metals, have elicited fascination among many condensed matter scientists because of their complex electronic properties. Now, researchers in Japan have demonstrated that a normal semiconductor can be transformed into a topological semi-metal by light irradiation. Further, they showed how spin-dependent responses could appear when illuminated with circularly-polarized laser light. Published in Physical Review B, this work explores the possibility of creating topological semi-metals and manifesting new physical properties by light control, which may open up a rich physical frontier for topological properties.

Most ordinary substances are either , like metals, or insulators, like plastic. In contrast, can exhibit unusual behavior in which electrical currents flow along the surface of the sample, but not inside the interior. This characteristic behavior is strongly connected to topological properties inherent in the electronic state. Furthermore, a novel phase called a topological semi-metal provides a new playground for exploring the role of topology in condensed matter. However, the underlying physics of these systems is still being pondered.

Researchers at the University of Tsukuba studied the dynamics of excitations in zinc arsenide (Zn3As2) when irradiated with a laser with circular polarization. Zinc arsenide is normally thought of as a narrow-gap semiconductor, which means that electrons are not free to move around on their own but can be easily propelled by energy from an external light source. Under the right conditions, the material can show a special topological state called a “Floquet-Weyl semi-metal,” which is a topological semi-metal coupled with light. In this case, the can be carried in the form of quasiparticles called Weyl fermions. Because these quasiparticles travel as if they have zero mass and resist becoming scattered, Weyl fermions can move easily through the material.

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