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PPO Journal of Industrial Physics Journal of Industrial Tor hee r Dark Matter Meets Atomic, Molecular,gnd 1 ۳ ۱۶ Crystals with a Mébius Twist Cold Collisions Get Charged Bringing into Focus the Debris of Heavy-Ion Collisions How a Superfluid Becomes a Bose-Einstein Condensate” Topological Magnetism Turns Elementary Airborne Spiders Drift on Multiple Silk Threads 3 

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ournal of Industrial PPO Journal of Industrial Physics Copyright! /Association= of New — Physics“ Message from the Pra ed Responsible Director ‏ی‎ LTE 7 am happy to announce the [aig ippy 5 publication of the first volume of the ‏اتب وک‎ Journal of Industrial Physics. Journal ‏ليا‎ ‎of Industrial Physics is published by ‏ل ها‎ Digaatoea the Association of New Technologies [EIA CMENU COL EC of Malek Ashtar University of 3 ۳: Technology. The mission of the journal am ratcmen is to create a suitable platform for 1 scientific technical, research, 8 4 fic. excl 10 educational and scientific exchanges ۲ 7 ee eee me ores Mohammadi Renani — in the field of physics and related @AQQIETT OCT O my lia fields and to integrate activities in the Hossein Omrani, field of laser and optics engineering., EQRES HEED CLUE EEL Daniel Expanding the borders of science and Fag alata 

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1.Dark Matter Meets Atomic, Molecular, and Optical Physics 4 into Focus 2.Acoustic rystals wi Crystals with a 3.Cold ‏خط الي‎ Get Mobius Twist 5.How a Superfluid Becomes a Bose-Einstein Condensate . Topological 7.Airborne Spiders Drift. 6 ‏أ‎ 2 on Multiple Silk Threads Magnetism Turns Elementary 

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Dark Matter Meets Atomic, Molecular, and Optical Physics ۰85۶21 ۲ 9 *Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA March 9, 2022¢ Physics 15, 32 A method for detecting dark matter using tiny levitated spheres could reach an unprecedented sensitivity to light dark matter particles. WwW Figure 1: The dark matter detection scheme proposed by Afek and co-workers consists of nanospheres (blue) held in optical traps (red). If a dark matter particle (black) scatters off a nanosphere, it transfers momentum (q) to the nanosphere. A laser beam (green) detects the change in the nanosphere’s position caused by this momentum transfer. 1 Journal of Industral Pee 

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Dark matter accounts for roughly 85% of the total mass in the Universe, yet its constituents remain unknown. Solving this mystery calls for a wide range of experiments that can detect dark matter constituents with different masses and interactions. Now, Gadi Afek at Yale University and colleagues have proposed a laboratory-based detector that is drastically different from existing experiments [1]. The detector works by measuring the momentum imparted when dark matter particles scatter off optically trapped nanometer- scale spheres. This approach provides an entirely new way to | éppreaekes, tar eteccig, ati, Haliesn BAN 1ReRA AYA Aledbegry. Hypothetical ۳ called weakly interacting massive particles (WIMPs) were a byproduct of many theories developed to extend the standard model of particle physics. WIMPs remain viable and well-motivated dark matter candidates with masses above about 1 GeV/c2 (roughly the mass of a proton). Other hypothetical particles known as axions remain attractive dark matter candidates for a range of masses below 100 meV/c2. Decades of searches for WIMPs and axions have so far co! up empty handed. However, the next few years will experiments—such as ADMX [2], LZ [3], and X1 

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the expected parameter space for these particles. This statement is by no means trivial: it took decades of vigorous technological development to get to this point. But what if dark matter is not WIMPs or axions? What other possibilities are there, and what opportunities arise for both theoretical model building and novel experimental approaches? Clearly, the significance of the dark matter problem mandates PRL ۳ Db BR” EARP Bde A" hee tb 23 Containing superfluid helium that can discern the tiny amounts of crystal-lattice vibrations generated when a dark matter particle hits a target atomic nucleus in the detector [8]. All these methods are optimized for the lowest- possible energy thresholds, which are particularly crucial Athindndkingvforkers: Gevioacank madteally different (Fig. 1). Instead of measuring the energy imparted when dark matter scatters off a target, the authors propose to directly detect the momentum transferred to the target. Instead of using macroscopic detectors with a large mass (typically, kilograms or even metric tons), they suggest using levitated spheres that are only nanometers across. And instead of. using detectors that rely on nuclear physics methodg, th, propose to use techniques from atomic, mole: optical physics. The nanospheres are optically, 

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Then their positions are read out with high precision by a second laser containing squeezed light—a state of light in which one component of quantum noise is lower than a fundamental limit called the standard quantum limit. The particular proposal calls for 10 dB of quantum-noise reduction relative to the stanquantum limit, which is challenging, but it has been demonstrated in similar systems [9]. dard The authors realized that the size of the trapped nanospheres can be tuned to optimize the sensitivity of the experiment to dark matter. If a light dark matter particle scatters off a nanosphere, the wavelength associated with the imparted momentum can be larger than the nanosphere. In that case, the scattering process will be coherent over the entire nanosphere: the dark matter particle will interact with all the nucleons (neutrons and protons) of the nanosphere at once. Basic quantum mechanics tells us that the probability of such scattering is calculated by adding up the individual dark matter-nucleon scattering amplitudes for each nucleon and then squaring the result. Therefore, the scattering probabilit) scales with the square of the number of nucleons. Fi nanosphere containing 106 nucleons, the probaby enhanced by a huge factor ( 1012). This effect, 

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However, for an experiment to be sensitive to dark matter, it is not enough to be able to detect dark matter signals. Crucially, the experiment also needs to be able to suppress or distinguish all relevant backgrounds that would otherwise mimic a dark matter signal. Afek and colleagues make the best effort to estimate known backgrounds for their levitated nanospheres. They find that interactions between residual gas particles and the nanospheres are tolerable in a routinely achievable ultrahigh vacuum; that thermal noise is acceptable at moderate cryogenic temperatures; and that a few other backgrounds should not swamp a dark matter signal. Backgrounds will limit the sensitivity of the proposed experiment and will drive its design and operation. For instance, to improve the signal-to-noise ratio, the experiment will need to be scaled up to a large array of nanospheres. Nevertheless, the prospects are thrilling. Should signals be seen, their dark matter origin could be disentangled from instrumental artifacts or other backgrounds through their momentum spectrum and through their dependence on thg nanosphere material. In addition, given that Earth complg one rotation each day, the direction of the imparted by dark matter is expected to e 

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Whether all these expectations hold true remains to be seen; the proposed experiment is not easy by any standard, and the requirements on its signal sensitivity and background control are extreme. Yet the authors are part of a small but growing community that is pursuing innovative detection methods, exploiting progress from atomic, molecular, and optical physics to address the dark matter problem [10]. The next few years will be very exciting. While conventional experiments are probing the most promising regions of the WIMP and axion parameter spaces, entirely novel detection schemes are being proposed, with potentially transformative improvements for the sensitivity of experiments to dark matter. 

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ع1 G. Afek et al., “Coherent scattering of low mass dark matter from optically trapped sensors,” Phys. Rev. Lett. 128, 101301 (2022). T. Braine et al. (ADMX Collaboration), “Extended search for the invisible axion with the Axion Dark Matter Experiment,” Phys. Rev. Lett. 124, 101303 (2020). D.S. Akerib et al. (LUX-ZEPLIN Collaboration), “Projected WIMP sensitivity of the LUX-ZEPLIN dark matter experiment,” Phys. Rev. D 101, 052002 (2020). E. Aprile et al. “Projected WIMP sensitivity of the XENONnT dark matter experiment,” J. Cosmol. Astropart. Phys. 2020, 031 (2020). L. Barak et al. (SENSEI Collaboration), “SENSEI: Direct- detection results on sub-GeV dark matter from a new Skipper CCD,” Phys. Rev. Lett. 125, 171802 (2020). A.H. Abdelhameed et al. (CRESST Collaboration), “First results from the CRESSTIII low-mass dark matter program,” Phys. Rev. D 100, 102002 (2019). R. Agnese et al. “First dark matter constraints from a SuperCDMS single-charge sensitive detector,” Phys. Rev. Lett. 121, 051301 (2018). S, A. Lyon et al., “Single phonon detection for dark matter via quantum evaporation and sensing of 3helium,” arXiv:2201.00738. L. Magrini et al, “Squeezed light from nanoparticle at room temperature, ” arXiv:2202.0932. ao sing ingg 4 0) 

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About the Author Rafael Lang is a professor of physics and astronomy at Purdue University, Indiana. He obtained his Ph.D. working on the CRESST dark matter search at the Max Planck Institute for Physics, Germany. He then joined the XENON Collaboration, _ first as a_ postdoctoral researcher at Columbia University and then at Purdue. He chairs the Supernova Early Warning System, which looks ۲ neutrinos from a Galactic supernova. He recently founded the Windchime Collaboration, which uses a large array of mechanical accelerometers to search for dark ‎Se‏ عا و ع يو يي ‎ 

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Acoustic Crystals with a Mobius Twist *Yuanchen Deng and Yun Jing ‘Graduate Program in Acoustics, College of Engineering, The Pennsylvania State University, University Park, PA, USA March 14, 2022+ Physics 15, 36 By manipulating symmetries in acoustic lattices, two independent groups have created a topological insulator with a new, exotic topology. Figure 1: Cartoon of a 2D acoustic lattice and the Mébius loop encoded in its topoplogy. BPO 

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The Mébius loop is an iconic geometry that shows the oddity of a topological transformation. One can easily construct this one-sided surface by twisting a strip of paper by 180° and sticking the ends of the strip together (Fig. 1). As topology has turned into a central topic in condensed-matter physics, an interesting question arises: Can a Mébius-like geometry interact with topological states and enrich them? Seeking an answer to that question, two groups of researchers from Nanyang Technological University, Singapore, and Wuhan University, China, respectively, have coupled a Mébius loop with the topological edge states of acoustic lattices—periodic arrays of acoustic resonators [1,2]. The experimental observations indicating that this system hosts a new class of “Mebiupdivisied” phaspslogisalopdiegdcal wihlatasake clark fundamental wasearrb panactignmiariraclogyaandomayplvagiéal neystalevisesn dom roenthallingo arousticnieny elartinagagtin W9H@hetries, in which the set of operations that leave the crystal structure unchanged has a fixed point. Other types of symmetries, however, remain largely unexplored, including those that involve translational symmetry displacement that is nonprimitive; that is, correspond to a multiple of a lattice vector. 

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In 2015, a theoretical model for a nonsymmorphic symmetry —a symmetry about a glide plane or screw axis, which cannot be described as a combination of translations and rotations— revealed a new route toward a Z, topological phase that does not involve antiunitary symmetries [3]. It was predicted that this new topological phase supports stable and gapless topological edge states with a Médbius twist in the band structures, leading to systems with such a topological phase being dubbed “Mébius insulators.” Mébius insulators have bands with a 4m periodicity in the projective translational symmetry direction—meaning that, like a finger tracing the surface of a Mébius strip, a particle must complete two circuits of the system before it returns to its initial location and phase. While researchers have been looking for Mébius insulators in various quantum systems [4- 6], topological acoustic lattices offer an alternative experimental path for finding these exotic systems as the Nanyang and Wuhan groups show. 

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Acoustic lattices have become fertile ground for investigating topological physics owing to the flexibility with which the hopping of acoustic waves between lattice sites can be manipulated. In acoustic lattices, this hopping, which corresponds to the hopping of electrons between lattice sites in electronic topological materials, is engineered using coupling tubes. Resonating cavities, meanwhile, provide the counterparts of the on-site orbitals in electronic topological materials. Using these components, researchers can not onc engigreboenmetdeahsynumetiigsekat beercontea tee ao Af dba aheuSAPRWAdrupole topological insulators [7, 8]. Acoustic quadrupole insulators provide some essential features of Mébius insulators—such as the n gauge flux, which describes how a particle hopping around a group of four neighboring lattice sites has its phase changed after one circuit. However, the challenging realization of a lattice with the nonsymmorphic symmetries that produce the Mébius topology has not yet been achieved. The Nanyang and Wuhan groups have found an alternative way to create this topology by replacing nonsymmorphic symmetries with a more easily realizable prgject symmetry (so called because it is created by a pug rimitive translation symmet 

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Figure 2: (Left) Photograph of the 2D acoustic lattice constructed by the Nanyang group. (Right) Schematic of the 3D acoustic lattice constructed by the Wuhan group. The researchers from Nanyang Technological University constructed a 2D acoustic lattice by combining cuboid acoustic resonators with coupling tubes, allowing the control of the sign of the hopping terms (Fig. 2) [1]. The 2D translational symmetry in such a lattice creates a fourfold degenerate Dirac point in the band structure. 

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Interestingly, the behavior of the band structure varies depending on how the symmetry is broken. The acoustic lattice shows topological edge-state bands featuring a Mébius twist when the translational symmetry is broken in the x direction, while the one in the y direction is preserved. The researchers observed these twisted gapless edge states, which are detached from the bulk bands, by measuring the acoustic pressure distributions on the xand y edges and determining the edge-state dispersion. If the translation symmetries in both the xand ydirections are broken, the acoustic lattice shows a graphene-like semimetal phase. In this case, a flat edge band exists on the edge parallel to the x direction, and this band connects the two Fermi points. The resaickings fonthwutasagureérsieg gastcdepantioduckdth Birexatnal aradiatoustidamerstraiesisthig GrantlapRnRrsees betaeoesticthésomtrs baepladiptihg RaBeS (Figd 2) ‏نوه‎ 01189 SESUPEsEGot only Mobius twisted edge states but also high- order topological states with energy confined at the hinges, which demonstrate that the projective symmetry can endow 3D systems with unique features. Given the extra dimension, 3D acoustic Médbius insulators show the capability engineering the topological order of acoustic lattic as the ability to route acoustic energy in the z di 

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The construction of acoustic Mébius insulators shows the potential of the acoustic lattice as a robust platform for pushing the frontiers of topology exploration in condensed- matter systems. It would be exciting to see whether the use of projective symmetry can be expanded to bring new physics to a large number of topological systems; projective inversion symmetry, for example, can be harnessed to achieve, in a spinless system, topological phases that would otherwise be unique to spinful systems and vice versa [9]. The generalization of these works will also benefit research in other systems carrying classical waves, such as electromagnetic and elastic waves, in which gauge fields can be readily realized. Finally, the observation of these new topological acoustic states may inspire new devices that feature extraordinary acoustic wave behaviors, such as the waveguiding of acoustic energy and the control of acoustic noise. 

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References 1H. Xue et al., “Projectively enriched symmetry and topology in acoustic crystals,” Phys. Rev. Lett. 128, 116802 (2022). 2.7. Li et al., “Acoustic Mébius insulators from projective symmetry,” Phys. Rev. Lett. 128, 116803 (2022). 3.K. Shiozaki et al., “Z2 topology in nonsymmorphic crystalline insulators: Mébius twist in surface states,” Phys. Rey. B 91, 155120 (2015). 4,Y. X. Zhao and A. P, Schnyder, “Nonsymmorphic symmetry- required band crossings in topological semimetals,” Phys. Rev. B 94, 195109 (2016). 5.P. Y. Chang et al., “Mébius Kondo insulators,” Nat. Phys. 13, 794 (2017). 6.R. X. Zhang et al., “Mébius insulator and higher-order topology in MnBi2nTe3n+1,” Phys. Rev. Lett. 124, 136407 (2020). 7.M. Serra-Garcia et al., “Observation of a phononic quadrupole topological insulator,” Nature 555, 342 (2018). 8.Y. Qi et al., “Acoustic realization of quadrupole topologic insulators,” Phys. Rev. Lett. 124, 206601 (2020). ‏لاو‎ X. Zhao et al., “Switching spinless topological phases with projective PT symm 

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About the Authors Yuanchen Deng received a B.S. in physics from Nanjing University, China in 2015. He is currently pursuing a Ph.D in the Graduate Program of Acoustics 2 ‏ب‎ ‎Pennsylvania State University. His research focuses on acoustic devices and structures inspired by topological physics 

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About the Authors Yun Jing received a B.S. in acoustics from Nanjing University, China, in 2006 and received an M.S, and later a Ph.D. from Rensselaer Polytechnic Institute, New York, in 2007 and 2009, respectively. He is currently an associate professor in the Graduate Program in Acoustics at Pennsylvania State University. His research interests B include physical acoustics and biomedical ultrasound. He is a fellow of the Acoustical Society of America and a senior member of IEEE. He has received numerous awards such as the 2018 R. Bruce Lindsay Award from the Acoustical Society of America, the 2018 IEEE Ultrasonics Early Career _ Investigator Award, the 2018 MIT 2 7 

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Cold Collisions Get Charged March 10, 2022+ Physics 15, 2 Researchers demonstrate that they can create molecules from lithium dimers and ytterbium ions, paving the way for quantum chemistry studies in a new type of system. 02 To understand the influence of quantum effects on a chemical reaction, scientists typically perform the reaction at ultracold temperatures, where they can more easily model the quantum collisions that produce molecules. Those collisions have been studied experimentally at ultralow temperatures for two atoms but not for the more complex scenario of an ion and a molecule. Now, Henrik Hirzler at the University of Amsterdam and his colleagues have changed that, observing ultracold reactions between ytterbium ions and lithium dimers [1]. The demonstration ands the kinds of reactions for which scientists ‏و‎ > quantum effects. 

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To make their molecules, the team took the following steps: First, they trapped a single ytterbium ion ( Yb+). Second, they prepared a cloud of ultracold lithium atoms and dimers. Third, they spatially overlapped the cloud and the ion. After letting the ion and atom cloud interact for 500 ms, they checked the هم ا ۱ present in the cloud, Yb+ was more likely to have stopped fluorescing after that time period, something that indicates a shift in the spacing between the ion’s energy levels. The team showed, using mass spectrometry, that this shift was due to ‏ی‎ Uehium dimer to form Yau aaa they can make molecular ions, they say that they hope to study in more detail the quantum effects involved in these reactions. They think that these ultracold molecules could also be used in quantum sensors and in searches for new physics. Rateacegnick ۱ ۱ ۳ ‏ریز‎ amie “Snserieaslanet Hanes WattorRased in Seatieashingioied ion and ultracold Feshbach dimers,” Phys. Rev. Lett. 128, 103401 (2022). 

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Bringing into Focus the Debris of Heav Ion Collisions March 9, 2022+ Physics 15, s26 A deblurring technique pioneered in optics could correct for measurement-induced smearing of particle distributions in a _ high-energy nuclear collision experiment. = * “Oa High-energy heavy-ion collisions create dense, hot nuclear matter. Researchers have been colliding such ions for 60 years. But issues with pinpointing some experimental parameters make it hard for them to determine some information about the collision debris, leading to “blurred” measurements. Now, Pawel Danielewicz of Michigan State University and Mizuki Kurata-Nishimura of RIKEN Nishina Center, Japan, propose a method for reducing these distortions [1]. SP Jounal of tndusal Phos 

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In a__ high-energy _heavy-ion-collision _ experiment, researchers collide two ions and then measure the energies and angles of the resulting particles. From these particles, they can coarsely assess the orientation at which the ions enter a collision. They then calculate averages for the orientations of the produced particles relative to that approximate ion orientation. But these averages come at the expense of resolution and detail: they forsake information on how particles get distributed relative to the precise orientation. To address this issue, Danielewicz and Kurata-Nishimura turned to a deblurring algorithm that is used in optics experiments to sharpen an image of an object that appears unfocused. Applying that algorithm to data simulations for a recent heavy-ion experiment at the Radioactive Isotope Beam Factory at RIKEN, the duo show that they can reverse the distortion of angular distributions caused by uncertainties in the colliding ions’ orientations. 

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In simulations, the duo also demonstrate that the optics algorithm can restore “true” angular distributions, relative to some fixed system orientation, in a manner akin to restoring car license plate numbers from blurred speed- camera photos. These corrected distributions provide 3D trajectory information about the system, giving a direct view into the central region of the hot, dense matter created during the collision. Danielewicz and Kurata-Nishimura say that this view could yield improved insights into high-energy collisions. -Rachel Berkowitz Rachel Berkowitz is a Corresponding Editor for Physics peed in Vancouver, Canada. References 1.P. Danielewicz and M. Kurata-Nishimura, “Deblurring for nuclei: 3D characteristics of heavy-ion collisions,” 

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How a Superfluid Becomes a Bose-Einste Condensate March 8, 2022¢ Physics 15, s33 Researchers have observed the spectrum of an ultracold atomic gas that can exist as a superfluid or a Bose-Einstein condensate in a study that could provide clues to the nature of superconductivity. Ultracold gases of fermionic atoms offer researchers a way to study quantum many-body phenomena using measurement techniques from atomic and molecular physics. In a new experiment, Hauke Biss of the University of Hamburg, Germany, and colleagues have used such a gas to measure the excitation spectrum of a quantum many-body system that undergoes a transition from a Bose-Einstein condensate (BEC) to a Bardeen- Cooper-Schrieffer (BCS) superfluid [1]. The results provide important benchmark data for theories of strongly interacting Fermi gases in settings such as neutron stars and unconventional superconductors. 7 2 1 ۱ 

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The team trapped a gas of fermionic lithium-6 atoms and, by tuning a magnetic field, varied how strongly the atoms interacted. Weakly interacting atoms produced a superfluid by forming relatively loosely bound Cooper pairs, analogous to the electron pairs in a conventional superconductor. Stronger interactions caused each atom to couple to many of its neighbors. Increasing the binding energy even further, the atoms paired up to form tightly bound, molecule-like bosons, condensing into a BEC. To study this "BEC-BCS crossover,” the team used lasers to generate excitations in the gas at different atomic interaction strengths. The spectra of these excitations near the crossover can provide clues about the nature of superconductivity, but until now it has been largely unexplored. 

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The researchers found that the measured spectrum agreed with theory in the BEC and crossover regimes, exhibiting a feature called the superfluid gap—an energy range where no excitations can occur. Toward the BCS regime, however, measurements and theory diverged. Biss and colleagues say that the discrepancy could help researchers improve theories of strongly correlated superfluids by, for instance, including a consistent description of particle-hole excitations that form as a result of particle-energy fluctuations. -Sophia Chen Sophia Chen is a freelance science writer based in Columbus, Ohio. References H. Biss et al., “Excitation spectrum and superfluid gap of an ultracold Fermi gas,” Phys. Rev. Lett. 128, 100401 (2022). 

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» Topological Magnetism Turns Elementar +Helen Walker ‘ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot, United Xangdom March 2 Neutron scattering Game provide the evidence of massless spin waves called Dirac magnons in a single- element magnetic crystal, offering a new window into 

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Figure 1: The magnon spectrum of gadolinium exhibits topological features. As shown in gadolinium’s Brillouin zone (left), there exists a nodal line (black), which extends along the 1 direction through the K point. The Dirac crossings along this line have an asymmetric pattern, represented by the color shading of the Dirac cones (right). ‏مهم وو وه هلر موه هوجو تلع موه ی ید رس‎ ‏تلهم مققآر0ن طكرج( 88 1349م‎ physics have a long history of successfully contributing to each other. For example, Philip Anderson’s work on superconductivity and symmetry breaking in 1963 [1] led to the development of the Higgs mechanism, which explains how particles acquire mass. More recently, concepts from particle physics have entered the realm of condensed matter with the observation that electrons in graphene move as if they were massless, obeying the relativistic Dirac equation for fermions [2]. This Dirac behavior has been observed in collective magnetic spin oscillations, or magnons. Owing to their massless property, Dirac magnons can propagate over longer distances without dissipating energy as heat—a potentially useful property i spintronics. Prior detections of Dirac magnons were ma 2D ferromagnets [3, 4] and 3D antiferromagnets [! 

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Now, Allen Scheie from Oak Ridge National Laboratory, Tennessee, and colleagues have observed Dirac magnons in pure elemental gadolinium, a 3D ferromagnet [6, 7]. The practically disorder-free crystal structure of gadolinium allows the researchers to obtain clean magnon spectra. The results reveal topological phases in adolinium and suggest that other elemental magnets ‏و ون ای از‎ NGS RR UML ‏ماق‎ ‎feat the band’ structure. ein m the case of graphene and other materials, such as topological insulators, the Dirac cone is observable as a linear crossing of the conduction and valence electronic bands. Near the crossing point, the electrons can be described by the Dirac equation, which was originally derived for the case of massless fermions. However, Dirac physics is not limited to fermions. Experiments have shown that bosons, such as magnons, plasmons, and phonons, can have Dirac crossings in their band structures. Magnons are quasiparticles describing quantized disturbances of the magnetic structure. These disturbances propagate as spin waves in roughly the same way as phonon excitations propagate as displacement wayg within the crystal lattice. Dirac crossings of magpgn } have previously been observed in a nug CoTiQ 

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Scheie and co-workers have now provided ‏ه‎ full characterization of the Dirac magnons in a single-element material, gadolinium (Ga). Gadolinium is a rare-Earth magnetic material that is used in nuclear-power generation, medical imaging, magnetic refrigeration, and solid oxide fuel cells. It is metallic, crystallizes in a hexagonal-close-packed structure (a simple 3D bipartite lattice), and becomes ferromagnetic at a critical temperature of 293 K. The material has near-perfect isotropy and vanishing spin-orbit coupling, making it a simple model system for studying magnon behavior. Scheie and colleagues studied Gd using inelastic neutron scattering at the Spallation Neutron Source at Oak Ridge National Laboratory. In this technique, neutrons, which have magnetic moments, create and annihilate magnons when they scatter from a Gd crystal. By measuring the energy lost by the neutrons during the scattering process, the researchers were able to identify magnon modes over all directions within the crystal lattice, going beyond previ, measurements that focused on only certain lattice, 

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The data were plotted in the Brillouin zone (BZ), the primitive unit cell in momentum space, which is a hexagonal prism in the case of Gd (Fig. 1). Points in the BZ are specified by the indices (hk), which are normalized with respect to the lattice spacing. Previous work had detected a linear Dirac crossing at the K point (1/3, 1/3 ,0), but the fuller picture provided by Scheie and colleagues reveals that the crossing is degenerate, extending along all values of the index 1. Such a feature is called a nodal line. The nodal line along | shows an anisotropic intensity pattern; in other words, the neutron scattering is greater on one side of the Dirac cone than on the other. The direction of this modulation is inverted for energies above and below the crossing point. This winding behavior is the signature of a topological phase called a Berry phase. The topological character of this phase is determined by Gd’s symmetries, which include both inversion and time-reversal symmetry. These same symmetries protect the magnon nodal lines from disorder that could affect the crossing. The calculations ‏رط‎ ‎Scheie and co-workers suggest that the nodal lines produgg 

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Moving along the nodal line, the Dirac cone flattens at 1=1/2 into a nodal plane—a degeneracy in the modes at all h and k. Electronic nodal planes were predicted in semimetals and have been observed at the Fermi surface of the topological material MnSi, but the team’s experiments provide the first experimental observation of a magnonic nodal plane. This magnon equivalent of an electronic nodal plane expands the set of analogies between topological magnets and topological electronic systems, which have proven very fruitful in extending knowledge of one system onto the other. The consequences of the nodal plane remain open to future study, with potential for topological magnon bands beyond Dirac cones. Gadolinium is not the only elemental, hexagonal-close-packed ferromagnet, as similar properties are found in other rare- Earth metals, such as terbium and dysprosium, and in hexagonal cobalt. Given the intrinsic connection between symmetry and topology, these related magnets might ho; similar magnon features, but their topology could be diffg because their magnetic interactions are more anigg those of Gd. Through theoretical modeling, 

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For example, they looked at the antisymmetric Dzyaloshinskii-Moriya exchange interaction, which breaks time-reversal symmetry. They found that this interaction lifts the nodal plane degeneracy while leaving the 1=1/2 nodal lines, potentially resulting in surface magnon modes with a preferred handedness, or chirality. Such chiral modes would depend on spin orientation and could be tuned with a magnetic field, but they could also be suppressed by effects like spin-orbit coupling. Further theoretical modeling is necessary to determine whether chiral surface modes could be observed. But gadolinium has opened the door to a new realm of possibilities in topological magnetism. 

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IDeA 1.P. W. Anderson, “Plasmons, Gauge Invariance, and Mass,” Phys. Rev. 130, 439 (1963). ferences 2.A. H. Castro Neto et al., “The electronic properties of graphene,” Rev. Mod. Phys. 81, 109 (2009). 3.L. Chen et al., “Topological spin excitations in honeycomb ferromagnet CrI3,” Phys. Rev. X 8, 041028 (2018); “Topological spin excitations in honeycomb ferromagnet CrI3,” 8, 041028 (2018). 4.B, Yuan et al., “Dirac magnons in a honeycomb lattice quantum XY magnet CoTi03,” Phys. Rev. X 10, 011062 (2020); M. Elliot et al., “Order-by-disorder from bond-dependent exchange and intensity signature of nodal quasiparticles in a honeycomb cobaltate,” Nat. Commun. 12, 3936 (2021). 5.W. Yao et al., “Topological spin excitations in a three- dimensional antiferromagnet,” Nat. Phys. 14, 1011 (2018); PB Bao, D. Y. Tsao, “Representation of multiple objects in macaque category-selective areas,” Nat. Commun. 9, 1774 (2018). 6.A. Scheie et al., “Dirac magnons, nodal lines, and nodal plane in elemental gadolinium,” Phys. Rev. Lett. 128, 097201 (2022), 7.. Scheie et al., “Spin-exchange Hamiltonian and topolg degeneracies in elemental gadolinium,” : 104402 (2022). 

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About the Authors Helen Walker is a staff scientist at the ISIS Neutron and Muon Source in the UK, specializing in exploring the collective dynamics of functional _ materials. She holds an undergraduate degree in natural sciences from the University of Cambridge and a Ph.D. in experimental condensed-matter physics from University College R London. Prior 16 becoming a neutron scientist, she worked at the European Synchrotron Radiation Facility in France and at PETRA III at DESY, Germany. Her research _ interests include magnetism in metal organic frameworks and structure-dynamics- property relations in barocalorics. She won the ESRF Young سس سس سس سس 2 

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Airborne Spiders Drift on Multiple 11 6 March 4, 2022¢ Physics 15, 31 Simulations reveal new details of the way spiders can fly by exploiting the electric field present in the SBMROSBRBEE: can float and drift like a balloon, with lift provided by electrostatic forces or air currents or both. Now researchers have simulated the process at a new level of detail and have shown the importance of the spatial arrangement of the threads that the spider emits and uses to fly [1]. In contrast to earlier models that involve only a single thread and some subset of environmental forces, the new simulations provide a complete description of the force balance that determines whether a spider balloons or stays on the ground. Explanations for spiders’ ability to float fall into two main categories. Both invoke forces that act on the silk threads a spider emits for this purpose, which can number in the hundreds, depending on the species. One idea is that when air warmed by the sun rises, the spider’s threads catch the updraft, The other hypothesis is that the atmosphere’s weak but ever-present vertical electric field acts on the threads’ static electric charge. Researchers have previously explored both hypotheses with experiments, but it’s difficult to observe the effects of airflow or electric fields on tiny, wispy threads. Simulations have been performed in one dimension and have assumed a single thread, even though multiple threads can havg siqpific: effects, says M. Khalid Jawed of the Universit ۱ Los Angeles. For example, in the electrostatic méwfan’m, lift force should be strongly affected by the spatial‘distribution 

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Now, Jawed and Charbel Habchi of Notre Dame University- Louaize in Lebanon have turned to an algorithm developed by the computer graphics community. “Several hit Hollywood movies, such as The Hobbit and the Planet of the Apes series, have used this formulation for fur and hair,” Habchi says. The algorithm divides each thread into many spaghetti-like segments that can bend, stretch, and twist. The simulations approximate an Erigone spider as a 2-mm-wide solid sphere with 2, 4, or 8 threads attached at the top, oriented vertically at the start. Each thread is coated with electric charges. The researchers accounted for gravity; the atmosphere’s electric eld, which decreases with height; the threads’ glectric charge: ‏ا‎ rest on the ground’ a is lifted by the electric. field. @ the charged, initially straight threads remain attached to the spider, their mutual repulsion causes them to spread apart over a period of time. As the spider accelerates upward, downward drag increases and—combined with the spider's weight—eventually cancels the lifting force. This competition between upward ani downward forces determines a spider’s final (termi upward velocity. 

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The researchers conclude that multiple threads, if charged, will retain an ordered arrangement rather than tangling, as they might in the absence of any charge or electric field. “We think that, at least for small spiders, the electric field, without any help from upward air currents, can cause ballooning,” says Habchi. However, larger spiders would require a boost from upward airflow. Habchi and Jawed found that their typical computed vertical velocities of 8.5 cm/s agreed with recent experimental studies of Erigone spiders enclosed in a chamber with a controllable electric field. They hope to observe ~~ “ats while measurir nd other environn Wingless flier. Erigone atra spider from North 

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Peter Gorham, a particle astrophysicist at the University of Hawaii who also studies spiders, says that the researchers “have tackled the mathematics associated with this complex classical mechanics problem with creativity and care.” Regarding the multithread dynamics, the researchers “demonstrate rigorously a conclusion that is intuitively simple yet challenging to prove.” The team also examined two different ways by which electric charge could be distributed on a thread. They performed the simulations assuming either a uniform distribution along the entire thread or a distribution localized at the thread’s tip. Those studies showed that both could generate the force necessary for lifting. Going beyond biology, Habchi says that the work could lead to new devices for environmental science. “This understanding could be helpful for designing new types of ballooning sensors as probes to explore atmospheric Py 3 tsi - ae Jawed oc Ralooning: dor for ‏هه‎ sede arid alba SH 

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Leading conferences and seminars پیشرفت‌های ابررسانایی و مغناطیس http://www. psi.ir/f/ASM1401 TZ 

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Leading conferences and seminars dg oho Melly len SE Uo gto = ‏اولین همایش‎ ‏پژوکش‌های کاربردی‎ ‏ممه‎ tn Baciie Stamass ‏كر هلهم يايه‎ PaaS ati AD T" national Conference on. ‎JL‏ مقاله قط از وبسایت قبل قبول میباشد آخرين مهلت ارسال مقالات: ‏2ج ‏اشيم با تكرش كاريردى فيزيكك ب تكرش كاريردى ارياضى با تكرش كاريردى روش های آماری در علوم بای ‎3 ‎© ‏آخرین میلت ثبتتام: ‎ ‎ 

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Journal of Industrial Next release time August 2022 hope to see you again