Wave Vector Research Articles

Geometrical Optics Stability Analysis of Rotating Visco-Diffusive Flows

Geometrical optics stability analysis has proven effective in deriving analytical instability criteria for 3D flows in ideal hydrodynamics and magnetohydrodynamics, encompassing both compressible and incompressible fluids. The method models perturbations as high-frequency wavelets, evolving along fluid trajectories. Detecting local instabilities reduces to solving ODEs for the wave vector and amplitude of the wavelet envelope along streamlines, with coefficients derived from the background flow. While viscosity and diffusivity were traditionally regarded as stabilizing factors, recent extensions of the geometrical optics framework have revealed their destabilizing potential in visco-diffusive and multi-diffusive flows. This review highlights these advancements, with a focus on their application to the azimuthal magnetorotational instability in magnetohydrodynamics and the McIntyre instability in lenticular vortices and swirling differentially heated flows. It introduces new analytical instability criteria, applicable across a wide range of Prandtl, Schmidt, and magnetic Prandtl numbers, which still remains beyond the reach of numerical methods in many important physical and industrial applications.

The spin-wave energy spectrum and transition temperature of the two-dimensional VSe2-like: a retarded Green’s function method study

Based on the recent discovery of intrinsic magnetism in monolayer films VSe2, we have constructed a two-dimensional (2D) Heisenberg model incorporating the 1Tand 2Hstructures. These configurations consist of three layers: the upper and lower surface layers and a middle layer. Using the retarded Green's function method, we investigate the spin-wave energy spectrum, spin-wave density of states, and transition temperature of the system. It is found that in the 2Hstructure, the spin-wave energy spectrum of the system exhibits three direct energy gaps, with one branch being independent of the wave vector. Further analysis shows that at this constant energy, a particular surface state emerges in the 2Hstructure. In contrast, the spin-wave energy spectrum in the 1Tstructure features only two energy gaps-one direct energy gap1 and one indirect energy gap3-without forming a unique surface state. Single-ion anisotropy and interlayer interactions between the upper and lower surface layers influence the energy gaps in the spin-wave energy spectrum and the system's transition temperature. This theoretical work sheds light on forming particular surface states in monolayer 2Hstructure magnetic materials. It provides crucial theoretical support for designing and fabricating next-generation low-dimensional magnetic random-access memory.

Simulation of ion cyclotron range of frequencies heating in the proton–boron plasma of the spherical tokamak

Abstract Ion cyclotron range of frequencies (ICRF) heating is crucial in magnetic confinement fusion devices that utilize proton–boron11 (p11B) as an advanced fuel, as it requires higher ion temperatures for their reactions. This work investigates the ICRF heating characteristics of hydrogen (H) ions at the second harmonic frequency and 11B ions at the fundamental frequency in a p11B plasma within a spherical tokamak. It is found that H ions second harmonic is better than 11B ions fundamental for ion power absorption. We simulate the ICRF heating effects of the 11B fraction in plasma and the wave vector parallel to the magnetic field ( k ‖ ) of the antenna using full-wave codes and the kinetic dispersion relation solver. In second harmonic heating of H ions, the power deposition primarily occurs on the H ions themselves, and, the total power absorption will exceed 50%, up to 58%, when X[11B] > 6%. Heating the electrons is easier in the fundamental frequency heating of 11B ions scenario.

Quadruple-Q Skyrmion Crystal in Centrosymmetric Body-Centered Tetragonal Magnets

We conduct a numerical investigation into the stability of a quadruple-Q skyrmion crystal, a structure generated by the superposition of four spin density waves traveling in distinct directions within three-dimensional space, hosted on a centrosymmetric body-centered tetragonal lattice. Using simulated annealing applied to an effective spin model that includes momentum-resolved bilinear and biquadratic interactions, we construct a magnetic phase diagram spanning a broad range of model parameters. Our study finds that a quadruple-Q skyrmion crystal does not emerge within the phase diagram when varying the biquadratic interaction and external magnetic field. Instead, three distinct quadruple-Q states with topologically trivial spin textures are stabilized. However, we demonstrate that the quadruple-Q skyrmion crystal can become the ground state when an additional high-harmonic wave–vector interaction is considered. Depending on the magnitude of this interaction, we obtain two types of quadruple-Q skyrmion crystals exhibiting the skyrmion numbers of one and two. These findings highlight the emergence of diverse three-dimensional multiple-Q spin states in centrosymmetric body-centered tetragonal magnets.

Probing quantum floating phases in Rydberg atom arrays

The floating phase, a critical incommensurate phase, has been theoretically predicted as a potential intermediate phase between crystalline ordered and disordered phases. In this study, we investigate the different quantum phases that arise in ladder arrays comprising up to 92 neutral-atom qubits and experimentally observe the emergence of the quantum floating phase. We analyze the site-resolved Rydberg state densities and the distribution of state occurrences. The site-resolved measurement reveals the formation of domain walls within the commensurate ordered phase, which subsequently proliferate and give rise to the floating phase with incommensurate quasi-long-range order. By analyzing the Fourier spectra of the Rydberg density-density correlations, we observe clear signatures of the incommensurate wave order of the floating phase. Furthermore, as the experimental system sizes increase, we show that the wave vectors approach a continuum of values incommensurate with the lattice. Our work motivates future studies to further explore the nature of commensurate-incommensurate phase transitions and their non-equilibrium physics.

Modified Heisenberg Commutation Relations, Free Schrödinger Equations, Tunnel Effect and Its Connections with the Black–Scholes Equation

This paper explores the implications of modifying the canonical Heisenberg commutation relations over two simple systems, such as the free particle and the tunnel effect generated by a step-like potential. The modified commutation relations include position-dependent and momentum-dependent terms analyzed separately. For the position deformation case, the corresponding free wave functions are sinusoidal functions with a variable wave vector k(x). In the momentum deformation case, the wave function has the usual sinusoidal behavior, but the energy spectrum becomes non-symmetric in terms of momentum. Tunneling probabilities depend on the deformation strength for both cases. Also, surprisingly, the quantum mechanical model generated by these modified commutation relations is related to the Black–Scholes model in finance. In fact, by taking a particular form of a linear position deformation, one can derive a Black–Scholes equation for the wave function when an external electromagnetic potential is acting on the particle. In this way, the Scholes model can be interpreted as a quantum-deformed model. Furthermore, by identifying the position coordinate x in quantum mechanics with the underlying asset S, which in finance satisfies stochastic dynamics, this analogy implies that the Black–Scholes equation becomes a quantum mechanical system defined over a random spatial geometry. If the spatial coordinate oscillates randomly about its mean value, the quantum particle’s mass would correspond to the inverse of the variance of this stochastic coordinate. Further, because this random geometry is nothing more than gravity at the microscopic level, the Black–Scholes equation becomes a possible simple model for understanding quantum gravity.

Polyadic Cantor potential of minimum lacunarity: Special case of super periodic generalized unified Cantor potential

Abstract To bridge the fractal and non-fractal potentials we introduce the concept of generalized unified Cantor potential (GUCP) with the key parameter $N$ which represents the potential count at the stage $S=1$. This system is characterized by total span $L$, stages $S$, scaling parameter $\rho$ and two real numbers $\mu$ and $\nu$. Notably, the polyadic Cantor potential (PCP) system with minimal lacunarity is a specific instance within the GUCP paradigm. Employing the super periodic potential (SPP) formalism, we formulated a closed-form expression for transmission probability $T_{S}(k, N)$ using the $q$-Pochhammer symbol and investigated the features of non-relativistic quantum tunneling through this potential configuration. We show that GUCP system exhibits sharp transmission resonances, differing from traditional quantum systems. Our analysis reveals saturation in the transmission profile with evolving stages $S$ and establishes a significant scaling relationship between reflection probability and wave vector $k$
through analytical derivations.

Effect of volume fractional change of nanoparticles on surface plasmon polariton

Abstract The dispersion relation of surface plasmon polaritons (SPPs) is investigated as a function of the volume fraction of silver nanoparticles at the interface between nanocomposite and atomic media. The increase in silver nanoparticle content significantly influences SPP propagation, which is crucial for advancing plasmonic technologies. As the volume fraction of silver nanoparticles increases from 0\% to 60\%, the real part of the SPP wave vector rises from \(2.5k_0\) to \(5.5k_0\), and the SPP wavelength decreases from \(\lambda_{sp} = 0.7\lambda\) to \(\lambda_{sp} = 0.3\lambda\). This also modifies the propagation length from \(40\lambda\) to \(20\lambda\) and reduces the penetration depth in the nanocomposite from 0.125 nm to 0.005 nm.

Manipulating continuous optical spectra in the wave vector domain by metalens.

Complete 2π cycling of a phase around a phase singularity leads to a rapid phase variation in the nearby zones and forms a sharp local k-vector peak. In this paper, the intensity distribution in the spatial domain is transformed into a k-vector distribution in the wave vector domain, and we prove that the local k-vector peak is generated at the point of minimum light field intensity. The local k-vector peak is sharper when the minimum point is closer to the phase singularity. The k-vector peak can be manipulated by controlling the minimum optical field intensity. A metalens is designed to generate sharp k-vector peaks for continuous wavelengths and linearly shift the positions of these peaks with the incident wavelength. This method transforms full-band continuous optical spectra from the spatial domain to the wave vector domain. The spectral resolutions over the wavelength range from 800 nm to 810 nm are less than 0.82 nm, and the optimal spectral resolution reaches 0.027 nm. This approach can be used in metasurface spectroscopy, providing what we believe to be a new way to improve spectral resolution.

Emergence and tunability of Fermi-pocket and electronic instabilities in layered Nickelates.

Layered Nickelates have gained intensive attention as potential high-temperature superconductors, showing similarities and subtle differences to well-known Cuprates. This study introduces a modelling framework to analyze the tunability of electronic structures by focusing on effective orbitals and additional Fermi pockets, mimicking doping or external pressure qualitatively. It investigates the role of the $3d_{z^2}$ orbital in interlayer hybridization, which leads to the formation of a second pocket in the Fermi surface. The resulting effective model also predicts specific charge and spin susceptibility in the form of Lindhard susceptibility at wave vector $\mathbf{q_{0}} = (\pi, \pi)$, which can be tuned by doping or pressure. These results provide valuable insights into tunable orbital contributions and their influence on potential ordering and electronic instabilities in Layered Nickelates.

On the Frequency of Internal Gravity Waves in the Atmosphere: Comparing Theory with Observations

This paper is devoted to the dynamics of the propagation of non-planetary scale internal gravity waves (IGWs) in the stratified atmosphere. We consider the system of equations describing internal gravity waves in three approximations: (1) the incompressible fluid approximation, (2) the anelastic gas (compressible fluid) approximation, and (3) a new approximation called the non-Boussinesq gas approximation. For each approximation, a different dispersion relation is given, from which it follows that the oscillation frequency of internal gravity waves depends on the direction of propagation, the horizontal and vertical components of the wave vector, the vertical gradient of the background temperature, and the background wind shear. In each of the three cases, the maximum frequency of internal gravity waves is different. Moreover, in the anelastic gas approximation, the maximum frequency is equal to the Brunt–Väisälä buoyancy frequency, and in the incompressible fluid approximation, it is larger than the Brunt–Väisälä frequency by a factor of 7≅2.6. In the model proposed in this paper, the value of the maximum frequency of internal gravity waves occupies an intermediate position between the above limits. The question arises: which of the above fluid representations adequately describe the dynamics of internal gravity waves? This paper compares the above theories with observational data and experiments.

Miniaturized inertial sensor based on high-resolution dual atom interferometry.

Atom interferometry shows high sensitivity for inertial measurements in the laboratory, but it faces difficulties in field applications because of a trade-off between sensitivity and size. Therefore, there is an urgent need to develop a small sensor with high resolution for measuring acceleration and rotation in inertial navigation applications. Presented here is a miniaturized inertial sensor capable of measuring acceleration and rotation simultaneously based on high-resolution dual atom interferometers. A sensor head is integrated within a volume of 100 l, in which the vacuum chambers are fabricated by bonding quartz-glass windows with epoxy resin. A photoelectric cabinet is composed of four 3U rack units by integrating optical modules and electronic units. Dual atom interference fringes with a contrast of 29% are observed, and the acceleration and rotation are measured simultaneously by extracting their phase shifts. By developing a temperature compensation method to eliminate phase drifts caused by the thermal deformation of the Raman mirrors and using wave vector reversal to eliminate the phase drifts independent of the direction of the wave vector, measurement resolutions of 40 ng at 518s and 6.1 nrad/s at 10 880s are achieved for acceleration and rotation, respectively, from Allan deviations.

Metacavities by harnessing the linear-crossing metamaterials.

The formed optical cavity mode intensively relies on the size and geometry of optical cavity. When the defect or impurity exists inside the cavity, the formed cavity mode will be destroyed. Here, we propose a metacavity consisting of arrays of linear-crossing metamaterials (LCMMs) with abnormal dispersion, where each LCMM offers both the directional propagation channel for all incident angles and the negative refraction across its neighboring LCMMs. Such metacavity can be efficiently excited by a point source, where the excited wave vector components propagate along the same optical path in the cavity. More importantly, the proposed metacavity possesses the remarkable feature of partial defect immunity and geometry robustness. Assisted by two-dimensional transmission lines with loaded-circuit elements, a metacavity with partial defect immunity has been experimentally realized. Our work offers a new avenue for designing optical resonators excited by the point source in integrated photonics, which is very useful for high-efficiency filters, ultrasensitive sensors, and enhancement of light-matter interactions.

Detecting Multipartite Entanglement Patterns Using Single-Particle Green's Functions.

We present a protocol for detecting multipartite entanglement in itinerant many-body electronic systems using single-particle Green's functions. To achieve this, we first establish a connection between the quantum Fisher information and single-particle Green's functions by constructing a set of witness operators built out of single electron creation and destruction operators in a doubled system. This set of witness operators is indexed by a momentum k. We compute the quantum Fisher information for these witness operators and show that for thermal ensembles it can be expressed as an autoconvolution of the single-particle spectral function. We then apply our framework to a one-dimensional fermionic system to showcase its effectiveness in detecting entanglement in itinerant electron models. We observe that the detected entanglement level is sensitive to the wave vector associated with witness operator. Our protocol will permit detecting entanglement in many-body systems using scanning tunneling microscopy and angle-resolved photoemission spectroscopy, two spectroscopies that measure the single-particle Green's function. It offers the prospect of the experimental detection of entanglement through spectroscopies beyond the established route of measuring the dynamical spin response.

Quasi-Two-Dimensional Antiferromagnetic Spin Fluctuations in the Spin-Triplet Superconductor Candidate CeRh_{2}As_{2}.

The tetragonal heavy-fermion superconductor CeRh_{2}As_{2} (T_{c}=0.3 K) exhibits an exceptionally high critical field of 14T for B∥c. It undergoes a field-driven first-order phase transition between superconducting states, potentially transitioning from spin-singlet to spin-triplet superconductivity. To further understand these superconducting states and the role of magnetism, we probe spin fluctuations in CeRh_{2}As_{2} using neutron scattering. We find dynamic (π,π) antiferromagnetic (AFM) spin correlations with an anisotropic quasi-two-dimensional correlation volume. Our data place an upper limit of 0.31 μ_{B} on the staggered magnetization of corresponding Néel orders at T=0.08 K. Density functional theory calculations, treating Ce 4f electrons as core states, show that the AFM wave vector connects significant areas of the Fermi surface. Our findings indicate that the dominant excitations in CeRh_{2}As_{2} for ℏω<1.2 meV are magnetic and suggest that superconductivity in CeRh_{2}As_{2} is mediated by AFM spin fluctuations associated with a proximate quantum critical point.

In Ukrainian

Due to its excellent electrical, mechanical, thermal and optical properties, graphene has attracted much interest since it was discovered in 2004. Its two-dimensional nature and other remarkable properties meet the needs of surface plasmons and have greatly enriched the field of plasmonics. The paper will review recent advances and applications of graphene in plasmonic, including theoretical mechanisms, experimental observations, and meaningful applications. Due to its flexibility and good tunability, graphene can be a promising plasmonic material as an alternative to noble metals. Optical conversion, plasmonic metamaterials, light harvesting, etc. have already been realized in graphene-based devices, which are useful for applications in electronics, optics, energy storage, THz technology, etc. In addition, the excellent biocompatibility of graphene makes it a very good candidate for applications in biotechnology and medical science. Surface plasmons in graphene offer a compelling route to many useful photonic technologies. As a plasmonic material, graphene offers several intriguing properties, such as excellent electro-optic tunability, crystal stability, large optical nonlinearity, and extremely high electromagnetic field concentration. Thus, recent demonstrations of surface plasmon excitation in graphene using near-infrared light scattering] have attracted great interest. Here we present an all-optical plasmonic coupling scheme that takes advantage of the intrinsic nonlinear optical response of graphene. To generate plasmons, pulses of visible light in a free in-plane graphene sheet are used using difference frequency mixing of the waves to match both the wave vector and the energy of the surface wave. By carefully controlling the phase with matching conditions, we show that it is possible to excite surface plasmons with a defined wave vector and direction in a wide frequency range with high photon efficiency. Prospects for the practical use of graphene in plasmonics are discussed.

Enhanced and directional fluorescence emission regulated by dual resonant surface modes

Fluorescence emission regulation is of great interest for its promising applications in various fields such as microscopy, chemical analysis, encryption, and sensing. Most studies focus on the regulation of the fluorescence emission process. However, the spectral separation of excitation and emission of fluorophores requires careful design of resonances to cover both emission and excitation wavelengths, which is a better choice to enhance fluorescence intensity. In this Letter, we engineer an efficient dielectric concentric ring grating on a dielectric multilayer film with two resonate modes to enhance the excitation and emission processes. By careful design of the structure, the two resonate modes occupy similar in-plane wave vector and overlap in the fluorescence area. Experimentally, fluorescence intensity enhancement about five times and the divergence of fluorescence into free space compressed to less than 5° are achieved. Our work provides what we believe to be a new strategy for the realization of high directional on-chip light emitter at room temperature.

N-dimensional Lomb Scargle Periodogram analysis of traveling ionospheric disturbances using ionosonde data

There is a multitude of wave-like phenomena in Earth’s ionosphere and thermosphere such as acoustic waves, gravity waves, planetary waves, tides, and Traveling Ionospheric Disturbances (TIDs) which are the ionospheric manifestation of atmospheric waves. These phenomena are often difficult to study since measurements are typically irregular in time and space due to geographic constraints for deploying ground instruments and the natural orbital motion of satellites. This frequently precludes Fourier methods such as the Fast Fourier Transform (FFT) from being used. The Lomb-Scargle Periodogram (LSP) provides FFT-like analysis when measurements are irregular. To our knowledge, all prior use of the LSP in space science has been one-dimensional. This paper uses a N-Dimensional extension of the LSP (ND LSP) to study traveling ionospheric disturbances in four dimensions on a quiescent day near solar minimum. We use an exquisite dataset consisting of 12 ionosondes over Australia on June 29, 2019. The ND LSP resolves the full 3-dimensional wave vector as well as the period for many discrete TIDs. To the degree possible, we validate our findings from ionosonde data processed with the ND LSP by using an FFT-based method on line-of-sight TEC data from the same period and find similar wavelengths and periods for the large TIDs. We show that TIDs occur preferentially near 70o elevation and could be missed or mischaracterized if using TEC data in the thin-shell approximation.

Research on the Modulation Characteristics of LiNbO3 Crystals Based on the Three-Dimensional Ray Tracing Method

To further study the electro-optical modulation characteristics of LiNbO3 crystals and analyze their modulation performance, a method for studying the modulation characteristics of LiNbO3 crystals, based on the three-dimensional ray tracing method, is introduced. With the help of the refractive index ellipsoidal theory, the optical properties of LiNbO3 crystals under the influence of the Pockels effect are systematically investigated. The research results show that the optical properties of LiNbO3 crystals under the action of an external electric field can be divided into two cases: the crystal optical axis is parallel to the clear light direction, and the crystal optical axis is perpendicular to the clear light direction. Subsequently, starting from Maxwell’s equation and the matter equation, the analytical expressions of optical parameters such as refractive index, wave vector, light vector, optical path, and phase delay in electro-optical crystals are derived. Finally, the propagation law of LiNbO3 crystals when the light is incident in any direction, i.e., when the optical axis of the crystal is parallel to the clear direction and perpendicular to the clear direction, and the light intensity and field of view of the LiNbO3 crystal for electro-optical modulation are discussed.

Ground-state magnetic structures of topological kagome metals RV6Sn6 (R=Tb,Dy,Ho,Er)

Magnetic kagome metals have attracted tremendous research interests recently, because they represent an ideal playground for exploring the fascinating interplay between their intrinsically inherited topologically nontrivial electron band structures, magnetism and electronic correlation effects, and the resultant novel electronic/magnetic states and emergent excitations. In this work, we report a comprehensive single-crystal neutron diffraction investigation of the ground-state magnetic structures of the recently discovered V-based topological kagome metals RV6Sn6 ( = Tb, Dy, Ho, Er). Furthermore, the sample synthesis details and our systematic studies of crystal structure, low-temperature magnetic and thermodynamic properties of these compounds via various in-house characterization techniques are also reported. Our single-crystal neutron diffraction measurements confirm that the long-range magnetic order forms below 4.3 K for R=Tb, 3.0 K for R=Dy, 2.4 K for R=Ho, and 0.6 K for R=Er, respectively. The ground-state magnetic structures of the studied compounds are comprehensively determined via the magnetic crystallography approaches. It can be revealed that RV6Sn6 (R = Tb, Dy, Ho) have a collinear ferromagnetic order in the ground state, with the ordered magnetic moment aligned along the c axis for R = Tb, Ho, while approximately 20∘ tilted off from the c axis for R = Dy. In contrast, ErV6Sn6 shows an A-type antiferromagnetic structure with a magnetic propagation vector = (0, 0, 0.5), and with the ordered magnetic moment aligned in the ab plane. The ordered magnetic moments are determined as 9.4(2) µB, 6.6(2) µB, 6.4(2) µB, and 6.1(2) µB for R = Tb, Dy, Ho, and Er, respectively. A comparison of the low-temperature magnetic structures for both the extensively investigated topological kagome metal series of RV6Sn6 and RMn6Sn6 is given in detail. This allows to gain new insights into the complex magnetic interactions, diverse single-ion magnetic anisotropies and spin dynamics in these compounds. The reported ground-state magnetic structures in RV6Sn6 (R = Tb, Dy, Ho, Er) can pave the way for further explorations of the possible interplay between magnetism and topologically nontrivial electron band structures in the magnetically ordered phase regime. Published by the American Physical Society 2024