Reviews in Physics最新文献

A wider scope in topological semimetals accelerates various attractive quantum phenomena for the last two decades. We here report the detailed investigation of magnetic Co₃Sn₂S₂ Weyl semimetal based on the cobalt accompanied kagome lattice for the first time. We emphasize the highly motivated theoretical and experimental analyses in each topological terms of Co₃Sn₂S₂ that led to intensifying emergent topological materials with inherent properties, particularly in the pursuance of magnetic rich quantum anomalous Hall effect. We additionally highlight the Co₃Sn₂S₂ surface band structure, recognized in the diverse fields of study from the perception of topological properties to modern electrochemistry approaches. From materials perspective, this typical kagome Co₃Sn₂S₂ Weyl semimetal alone has extensively covered more enriching nontrivial surface states than topological insulators and nonmagnetic semimetals even in the absence of magnetic field and external strain. Some specific examples include Weyl nodes linked flat band magnetism, a large anomalous Hall effect, anomalous Hall angle, giant magnetooptical effect, and thermomagnetic Nernst effect. In addition, we selectively extend the review on the undisputed surface band characteristics of Co₃Sn₂S₂, by which a major concept of magnetic Weyl semimetal could hierarchically meet the contemporary quantum phenomena. This strongly led to more focus on nontrivial magnetic topological studies for gaining insightful perspectives.

Since 2003, a new family of states without a clear theoretical interpretation has been measured in the heavy quarkonium spectrum, the so-called $XYZ$ states. While the nature of these states is so far unclear, the experimental search is one of the most active fields in the intensity frontier. In this review, the most important and representative results obtained in this field in recent years are going to be illustrated, providing insights into the nature of these exotic states. The focus will be on the experimental side, describing how it is possible to investigate their exotic nature with respect to the conventional quarkonium states.

Between the years 2015 and 2019, members of the Horizon 2020-funded Innovative Training Network named “AMVA4NewPhysics” studied the customization and application of advanced multivariate analysis methods and statistical learning tools to high-energy physics problems, as well as developed entirely new ones. Many of those methods were successfully used to improve the sensitivity of data analyses performed by the ATLAS and CMS experiments at the CERN Large Hadron Collider; several others, still in the testing phase, promise to further improve the precision of measurements of fundamental physics parameters and the reach of searches for new phenomena. In this paper, the most relevant new tools, among those studied and developed, are presented along with the evaluation of their performances.

The conventional definition of electric polarization as the “dipole moment per unit volume” is valid only for the special case of well-separated dipoles. An alternative general approach is to view polarization as a characteristic not of a single charge distribution but rather of an adiabatic transition between two nearby states. Polarization can then be rigorously defined as the integral of the current density over that transition. In contrast with the “Modern Theory of Polarization,” which is fully quantum-mechanical, in this paper polarization is considered from the classical perspective. Such treatment is less fundamental but simpler, has pedagogical advantages and, importantly, is subject to fewer constraints. Polarization can be rigorously and unambiguously defined for periodic or nonperiodic charge distributions, finite or infinite, microscale or macroscale, electrically neutral or non-neutral, continuous or discrete, at any temperature; polarization can be spontaneous or induced. A previous classical (non-quantum) analysis by Russakoff (Am J Phys 1970) was (i) limited to the Clausius–Mossotti/Lorenz–Lorentz model of molecular dipoles, and (ii) involves multipole expansions, which the analysis of this paper shows to be redundant.

The traditional dipole model of polarization is a straightforward special case of the proposed definition. A number of illustrative examples are presented.

Engineering nanostructures with exceptionally high-Q resonances mediated by the Fano-type hybridization between discrete states associated with the periodicity of the structure and broadband resonances excited on constituent scatterers are the emerging field in optics and photonics. These collective lattice resonances (CLRs) attracted a lot of attention in recent years due to a number of their exciting applications in sensing, optical filtering, structural color printing, fluorescence enhancement, nanoscale lasing, and nonlinear optics, which resulted in a rapidly growing number of fundamental and experimental studies. CLRs have been discovered for arrays of plasmonic metal nanoparticles with strong electric dipole resonances nearly four decades ago. Thereafter, the scope of CLRs has gradually extended to all-dielectric and magneto-optical nanoparticles, 2D materials and other types of constituents, which has broadened the range of CLRs applicability and enriched their properties. We provide a comprehensive review of the recent progress in this field with a special emphasis on advances far beyond plasmonics.

BaBiO₃ is an oxide perovskite with a wide variety of interesting properties. It was expected that the compound would behave like a metal. However, experiments revealed that BaBiO₃ is not metallic, which started an extensive debate about the mechanism responsible for this insulating behavior. The two most important conjectures in this debate are charge disproportionation of the Bi ion into 3+ and 5+ cations and bond hybridization of the Bi 6s and O 2p orbitals. Both mechanisms induce a breathing mode of the oxygen octahedra, which is experimentally observed in single crystals and thin films. Recently, ultra-thin BaBiO₃ films were studied with the aim of suppressing the breathing mode, which was expected to result in re-emergence of metallicity. However, this expectation was not confirmed so far. Furthermore, theoretical calculations predict that BaBiO₃ becomes a topological insulator (TI) when doped with electrons. Since high-temperature superconductivity was observed when doping the compound with holes, an interface between a superconductor and a TI can be established within the same parent compound. In this Review, we discuss the theoretical and experimental findings concerning the mechanism responsible for the unexpected insulating behavior of BaBiO₃ for both single crystals and thin films. An overview is given of the current state of the art and the experimental challenges of achieving an oxide topological insulating state in BaBiO₃.

Colliders have been at the forefront of discovery in particle physics for more than half a century. Building on the success of the Large Hadron Collider (LHC), the field of particle physics has been developing and reviewing the scientific cases for the colliders to succeed the LHC in the context of regional and international review and long-term planning processes. The aim is to reach consensus about which new collider or even colliders to build. This collider would determine the future direction of the field of particle physics and, ideally, lead to solutions to unanswered questions and problems with the Standard Model. We will provide a short overview of the current proposals for different colliders for the high-energy frontier and their proposed run plans. It will focus on comparing and contrasting their physics potential, while also placing them in their historical context.

Surface plasmon polaritons (SPPs) can achieve light transmission beyond the diffraction limit due to their special dispersion relationship. As a novel two-dimensional material, graphene has attracted extensive attention in recent years because of its unique band structure, excellent electronic and optical properties, and ability to support SPPs transmission on its surface. Graphene surface plasmon polaritons (GSPPs) are characterized by high carrier mobility, strong localization, low consumption and high tunability. It has functional and future applications in the transmission of optical knowledge, photodetectors, surface plasmon waveguides, metamaterials and nanolasers.

We comprehensively review the deceptively simple concept of dipole scattering in order to uncover and resolve all ambiguities and controversies existing in the literature. First, we consider a point electric dipole in a non-magnetic environment as a singular point in space whose sole ability is to be polarized due to the external electric field. We show that the postulation of the Green’s dyadic of the specific form provides the unified description of the contribution of the dipole into the electromagnetic properties of the whole space. This is the most complete, concise, and unambiguous definition of a point dipole and its polarizability. All optical properties, including the fluctuation–dissipation theorem for a fluctuating dipole, are derived from this definition. Second, we obtain the same results for a small homogeneous sphere by taking a small-size limit of the Lorenz–Mie theory. Third, and most interestingly, we generalize this microscopic description to small particles of arbitrary shape. Both bare (static) and dressed (dynamic) polarizabilities are defined as the double integrals of the corresponding dyadic transition operator over the particle’s volume. While many derivations and some results are novel, all of them follow from or are connected with the existing literature, which we review throughout the paper.

This document summarises the current theoretical and experimental status of the di-Higgs boson production searches, and of the direct and indirect constraints on the Higgs boson self-coupling, with the wish to serve as a useful guide for the next years. The document discusses the theoretical status, including state-of-the-art predictions for di-Higgs cross sections, developments on the effective field theory approach, and studies on specific new physics scenarios that can show up in the di-Higgs final state. The status of di-Higgs searches and the direct and indirect constraints on the Higgs self-coupling at the LHC are presented, with an overview of the relevant experimental techniques, and covering all the variety of relevant signatures. Finally, the capabilities of future colliders in determining the Higgs self-coupling are addressed, comparing the projected precision that can be obtained in such facilities. The work has started as the proceedings of the Di-Higgs workshop at Colliders, held at Fermilab from the 4th to the 9th of September 2018, but it went beyond the topics discussed at that workshop and included further developments. FERMILAB-CONF-19-468-E-T, LHCHXSWG-2019-005