Hasil untuk "Atomic physics. Constitution and properties of matter"

A. Akrap, D. Bordelon, S. Chatterjee et al.

We present recommendations to improve reproducibility and replicability in condensed matter physics. This area of physics has consistently produced both fundamental insights into the workings of matter and transformative inventions. Our recommendations result from a collaboration that includes researchers from academia and government laboratories, scientific journalists, legal professionals, representatives of publishers, professional societies, and other experts. The group met in person in May 2024 at a conference at the University of Pittsburgh to discuss the growing challenges related to research reproducibility and replicability in condensed matter physics. In this report, we discuss best practices and policies at all stages of the scientific process to safeguard the value of condensed matter. We hope this report will lay the groundwork for a broader conversation to develop subfield-specific recommendations.

Gilad Kishony, Ori Grossman, Netanel Lindner et al.

Abstract We consider two-dimensional periodically driven systems of fermions with particle-hole symmetry. Such systems support non-trivial topological phases, including ones that cannot be realized in equilibrium. We show that a space-time defect in the driving Hamiltonian, dubbed a “time vortex,” can bind π Majorana modes. A time vortex is a point in space around which the phase lag of the Hamiltonian changes by a multiple of 2π. We demonstrate this behavior on a periodically driven version of Kitaev’s honeycomb spin model, where $${{\mathbb{Z}}}_{2}$$ Z 2 fluxes and time vortices can realize any combination of 0 and π Majorana modes. We show that a time vortex can be created using Clifford gates, simplifying its realization in near-term quantum simulators.

Qiong Qin, Yi-feng Yang

Abstract Can room temperature superconductivity be achieved in correlated materials under ambient pressure? Our answer to this billion-dollar question is probably no, at least for realistic models within the current theoretical framework. This is shown by our systematic simulations on the pairing instability of some effective models for two-dimensional superconductivity. For a square lattice model with nearest-neighbour pairing, we find a plaquette state formed of weakly-connected 2 × 2 blocks for sufficiently large pairing interaction. The superconductivity is suppressed on both sides away from its melting quantum critical point. Thus, the magnitude of T c is constrained by the plaquette state for the d-wave superconductivity, in resemblance of other competing orders. We then extend our simulations to a variety of effective models covering nearest-neighbour or onsite pairings, single layer or two-layer structures, intralayer or interlayer pairings, and find an intrinsic maximum of the ratio T c /J ≈ 0.04−0.07, where J is the pairing interaction, given by the onsite attractive interaction in the attractive Hubbard model or the exchange interaction in the repulsive Hubbard model. Our results agree well with previous quantum Monte Carlo simulations for the attractive Hubbard model. Comparison with existing experiments supports this constraint in cuprate, iron-based, nickelate, and heavy fermion superconductors, despite that these compounds are so complicated well beyond our simplified models. As a result, the known families of unconventional superconductivity, possibly except the infinite-layer nickelates, seem to almost exhaust their potentials in reaching the maximal T c allowed by their respective J, while achieving room temperature superconductor would require a much larger J beyond 400–700 meV, which seems unrealistic in existing correlated materials and hence demands novel pairing mechanisms. The agreement also implies some deep underlying principles of the constraint that urge for a more rigorous theoretical understanding.

Hyeok Yoon, Yun Suk Eo, Jihun Park et al.

Abstract Uranium ditelluride (UTe2) is the strongest contender to date for a p-wave superconductor in bulk form. Here we perform a spectroscopic study of the ambient pressure superconducting phase of UTe2, measuring conductance through point-contact junctions formed by metallic contacts on different crystalline facets down to 250 mK and up to 18 T. Fitting a range of qualitatively varying spectra with a Blonder-Tinkham-Klapwijk (BTK) model for p-wave pairing, we can extract gap amplitude and interface barrier strength for each junction. We find good agreement with the data for a dominant p y -wave gap function with amplitude 0.26 ± 0.06 meV. Our work provides spectroscopic evidence for a gap structure consistent with the proposed spin-triplet pairing in the superconducting state of UTe2.

Pasquale Ercolano, Mikkel Ejrnaes, Ciro Bruscino et al.

Detectors capable of resolving the number of photons are essential in many applications, ranging from classic photonics to quantum optics and quantum communication. In particular, photon-number-resolving detectors based on arrays of superconducting nanostrips can offer a high detection efficiency, a low dark count rate, and a recovery time of a few nanoseconds. In this work, we use a detector of this kind for the unbiased generation of random numbers by following two different methods based on the detection of photons. In the former, we exploit the property that the light is equally distributed on each strip of the entire detector, whereas in the latter, we exploit the fact that, for a high average number of photons, the parity of the Poisson distribution of the number of photons emitted by the laser tends to be zero. In addition, since these two methods are independent, it is possible to use them at the same time.

Soronzonbold Otgonbaatar, Dieter Kranzlmuller

This article examines the current status of quantum computing (QC) in Earth observation and satellite imagery. We analyze the potential limitations and applications of quantum learning models when dealing with satellite data, considering the persistent challenges of profiting from quantum advantage and finding the optimal sharing between high-performance computing (HPC) and QC. We then assess some parameterized quantum circuit models transpiled into a Clifford+T universal gate set. The T-gates shed light on the quantum resources required to deploy quantum models, either on an HPC system or several QC systems. In particular, if the T-gates cannot be simulated efficiently on an HPC system, we can apply a quantum computer and its computational power over conventional techniques. Our quantum resource estimation showed that quantum machine learning (QML) models, with a sufficient number of T-gates, provide the quantum advantage if and only if they generalize on unseen data points better than their classical counterparts deployed on the HPC system and they break the symmetry in their weights at each learning iteration like in conventional deep neural networks. We also estimated the quantum resources required for some QML models as an initial innovation. Lastly, we defined the optimal sharing between an HPC+QC system for executing QML models for hyperspectral satellite images. These are a unique dataset compared with other satellite images since they have a limited number of input quantum bits and a small number of labeled benchmark images, making them less challenging to deploy on quantum computers.

A. A. Alzubadi, S. M. Aldulaimi

The present study focuses on the deformation of neutron-rich nuclei near the neutron drip line. The nuclei of interest include 28O, 42Si, 58Ca, 80Ni, 100Kr, 122Ru, 152Ba, 166Sm, and 176Er. The relativistic Hartree - Bogoliubov (RHB) approach with effective density-dependent point coupling is utilized to investigate the triaxial deformation, and Skyrme - Hartree - Fock + Bardeen - Cooper - Schrieffer is used to analyze the axial deformation. The study aimed to understand the interplay between nuclear forces, particle interactions, and shell structure to gain insights into the unique behavior of neutron-rich nuclei. Despite these nuclei containing magic numbers, their shapes are still affected by the nucleons' collective behavior and energy levels. As the number of neutrons increases, the shape smoothly transitions from spherical to triaxial and then to prolate. The axial deformation analysis confirmed the results of the triaxial deformation analysis using the RHB method. An imbalance in the number of protons and neutrons can affect pairing energy, where extra neutrons can reduce overall pairing energy, and protons can disrupt the nucleon pairing due to stronger Coulomb repulsion between them.

Xuetao Di, Haoran Ji, Wenshuai Gao et al.

Abstract Topological semimetals, possessing topologically non-trivial band structures, serve as excellent platforms for realizing topological superconductivity through hard point-contact experiments. In this study, we successfully induce superconductivity in the three-dimensional Dirac semimetal, cubic PtBi2, using ferromagnetic and paramagnetic tips in hard point contact experiments. The induced superconductivity is proven to be insensitive to ferromagnetism and exhibits unconventional features in the point-contact spectra. The highest superconducting transition temperature ( T c $T_{\mathrm{c}}$ ) reaches approximately 5.1 K, and the T c $T_{\mathrm{c}}$ values are proven to have a positive correlation with the coupling between the tip and the sample. Furthermore, we extend our point-contact experiments to trigonal PtBi2, a material possessing a type-I Weyl semimetal band structure and triply degenerate points proximate to the Fermi level. Utilizing both ferromagnetic Ni tips and paramagnetic Ag tips, we successfully enhance superconductivity with a T c $T_{\mathrm{c}}$ of up to 3.0 K in this material. The findings from point-contact measurements reveal that the enhanced superconductivity is compatible with ferromagnetism and the magnetism of the tip can affect the symmetry of the enhanced superconducting state. Given that the lattice structure remains stable under pressure up to 51.2 GPa for cubic PtBi2 and 12.9 GPa for trigonal PtBi2, the emergent superconducting states observed in these two PtBi2 materials could inherit their topological nontrivial nature and be promising candidates for topological superconductor.

Mikhail Mamaev, BM@N Collaboration

Peter Athron, Csaba Balázs, Andrew Fowlie et al.

Gravitational waves (GWs) were recently detected for the first time. This revolutionary discovery opens a new way of learning about particle physics through GWs from first-order phase transitions (FOPTs) in the early Universe. FOPTs could occur when new fundamental symmetries are spontaneously broken down to the Standard Model and are a vital ingredient in solutions of the matter anti-matter asymmetry problem. The purpose of our work is to review the path from a particle physics model to GWs, which contains many specialized parts, so here we provide a timely review of all the required steps, including: (i) building a finite-temperature effective potential in a particle physics model and checking for FOPTs; (ii) computing transition rates; (iii) analyzing the dynamics of bubbles of true vacuum expanding in a thermal plasma; (iv) characterizing a transition using thermal parameters; and, finally, (v) making predictions for GW spectra using the latest simulations and theoretical results and considering the detectability of predicted spectra at future GW detectors. For each step we emphasize the subtleties, advantages and drawbacks of different methods, discuss open questions and review the state-of-art approaches available in the literature. This provides everything a particle physicist needs to begin exploring GW phenomenology.

M. F. Hansen, J.-B. Vaney, C. Lepoittevin et al.

Abstract Pnictogens and chalcogens are both viable anions for promoting Fe-based superconductivity, and intense research activity in the related families has established a systematic correlation between the Fe-anion height and the superconducting critical temperature T c, with an optimum Fe-anion height of ~1.38 Å. Here, we report the discovery of superconductivity in the compound LaFeSiO1−δ that incorporates a crystallogen element, Si, and challenges the above picture: considering the strongly squeezed Fe–Si height of 0.94 Å, the superconducting transition at T c  = 10 K is unusually high. In the normal state, the resistivity displays non-Fermi-liquid behavior while NMR experiments evidence weak antiferromagnetic fluctuations. According to first-principles calculations, the Fermi surface of this material is dominated by hole pockets without nesting properties, which explains the strongly suppressed tendency toward magnetic order and suggests that the emergence of superconductivity materializes in a distinct set-up, as compared to the standard s ±- and d-wave electron-pocket-based situations. These properties and its simple-to-implement synthesis make LaFeSiO1−δ a particularly promising platform to study the interplay between structure, electron correlations, and superconductivity.

A. I. Sanzhur

The application of the van der Waals equation of state to the asymmetric nuclear matter is considered in a critical state region. The corrections to the van der Waals pressure and free energy due to the Fermi statistics are obtained starting from the Thomas - Fermi entropy expression which ensures the fulfilment of the Nernst theorem. The derived corrections account for the effective nucleon mass and neutron-proton isotopic asymmetry. The parameters of the van der Waals equation of state are deduced by taking the experimental value of critical temperature for symmetric nuclear matter and testing the model of van der Waals with statistics corrections included against the theory of Skyrme energy density functional. A critical line in pressure-temperature-composition space is considered. The incompressibility coefficient is determined along the critical line as a function of nuclear matter composition. A jump in the value of specific heat upon crossing a critical line is discussed.

Yu. G. Shchepkin, N. I. Mazina, V. I. Slisenko et al.

The method for determination of f-activity (spontaneous fission) of samples based on a combination of multiplicity spectrometry, measurement of radiation energy, and registration of time of long-range fission products is considered. The method is representative, highly sensitive, and fast. The minimum determined value of the specific activity is 1.4⋅10-3 Bq/g.

Sang-Wook Cheong, Xianghan Xu

Abstract Chirality with all broken mirror symmetries matters ubiquitously from DNA functionality, vine climbing, to the piezoelectricity of quartz crystals. Magnetic chirality means chirality in spin-ordered states or (atomic-scale or mesoscopic) spin textures. Magnetic chirality does not change with time-reversal operation, and chirality prime ( $${\mathcal{C}}^\prime$$ C ′ ) means that time-reversal symmetry in addition to all mirror symmetries is broken with free spatial rotations. We will discuss a few examples of magnetic chirality and $${\mathcal{C}}^\prime$$ C ′ , and their emergent physical properties. Some of these exotic properties have been recently observed, and many of them need to be experimentally confirmed.

Federico Battiston, Enrico Amico, Alain Barrat et al.

Complex networks have become the main paradigm for modelling the dynamics of interacting systems. However, networks are intrinsically limited to describing pairwise interactions, whereas real-world systems are often characterized by higher-order interactions involving groups of three or more units. Higher-order structures, such as hypergraphs and simplicial complexes, are therefore a better tool to map the real organization of many social, biological and man-made systems. Here, we highlight recent evidence of collective behaviours induced by higher-order interactions, and we outline three key challenges for the physics of higher-order systems.

F. Caglieris, C. Wuttke, X. C. Hong et al.

Abstract The nematic instability is an undebatable ingredient of the physics of iron-based superconductors. Yet, its origin remains enigmatic as it involves a fermiology with an intricate interplay of lattice-, orbital-, and spin degrees of freedom. It is well known that thermoelectric transport is an excellent probe for revealing even subtle signatures of instabilities and pertinent fluctuations. In this paper, we report a strong response of the thermoelectric transport properties of two underdoped 1111 iron-based superconductors to a vanishingly small strain. By introducing the strain derivative of the Seebeck and the Nernst coefficients, we provide a description of the nematic order parameter, proving the existence of an anisotropic Peltier-tensor beside an anisotropic conductivity tensor. Our measurements reveal that the transport nematic phenomenology is the result of the combined effect of both an anisotropic scattering time and Fermi surface distortions, pointing out that in a realistic description, abreast of the spin fluctuations also the orbital character is a fundamental ingredient. In addition, we show that nematic fluctuations universally relax in a Curie–Weiss fashion above T S in all the elasto-transport measurements and we provide evidences that nematicity must be band selective.

Joseph A. M. Paddison, Georg Ehlers, Andrew B. Cairns et al.

Abstract In partially ordered magnets, order and disorder coexist in the same magnetic phase, distinct from both spin liquids and spin solids. Here, we determine the nature of partial magnetic ordering in the canonical frustrated antiferromagnet Gd2Ti2O7, in which Gd3+ spins occupy a pyrochlore lattice. Using single-crystal neutron-diffraction measurements in applied magnetic field, magnetic symmetry analysis, inelastic neutron-scattering measurements, and spin-wave modeling, we show that its low-temperature magnetic structure involves two propagation vectors (2-k structure) with suppressed ordered magnetic moments and enhanced spin-wave fluctuations. Our experimental results are consistent with theoretical predictions of thermal fluctuation-driven order in Gd2Ti2O7, and reveal that inelastic neutron-scattering measurements on powder samples can solve the longstanding problem of distinguishing single-k and multi-k magnetic structures.

Chen-Kai Qiao, Shin-Ted Lin, Hsin-Chang Chi et al.

The millicharged particle has become an attractive topic to probe physics beyond the Standard Model. In direct detection experiments, the parameter space of millicharged particles can be constrained from the atomic ionization process. In this work, we develop the relativistic impulse approximation (RIA) approach, which can duel with atomic many-body effects effectively, in the atomic ionization process induced by millicharged particles. The formulation of RIA in the atomic ionization induced by millicharged particles is derived, and the numerical calculations are obtained and compared with those from free electron approximation and equivalent photon approximation. Concretely, the atomic ionizations induced by mllicharged dark matter particles and millicharged neutrinos in high-purity germanium (HPGe) and liquid xenon (LXe) detectors are carefully studied in this work. The differential cross sections, reaction event rates in HPGe and LXe detectors, and detecting sensitivities on dark matter particle and neutrino millicharge in next-generation HPGe and LXe based experiments are estimated and calculated to give a comprehensive study. Our results suggested that the next-generation experiments would improve 2-3 orders of magnitude on dark matter particle millicharge $δ_χ$ than the current best experimental bounds in direct detection experiments. Furthermore, the next-generation experiments would also improve 2-3 times on neutrino millicharge $δ_ν$ than the current experimental bounds.

Shuji Hasegawa

Abstract Thanks to advances in in situ measurement techniques for electrical transport in ultra-high vacuum together with emergent materials such as Rashba-type surfaces, topological insulators, atomic-layer superconductors, and 2D materials like graphene, surface states and edge states on crystals provide intriguing topics, e.g. dissipation-less currents, spin-polarized electric current, and pure spin current. This is due to broken symmetry and strong spin–orbit and electron–phonon interactions. Here we review some examples of experimental techniques of multi-probe methods at macroscopic and microscopic scales, followed by transport phenomena revealed by them. These are opening a field in condensed matter physics driven by symmetry breaking at surfaces and atomic layers.

Maria Patmiou, V. G. Karpov

Expanding on our former hypothesis that, in the current information age, teaching physics should become more intuition-based and aiming at pattern recognition skills, we present multiple examples of qualitative methods in condensed matter physics. They include the subjects of phonons, thermal and electronic properties of matter, electron-phonon interactions and some properties of semiconductors.