Wave Vector Research Articles

Propagation dynamics of dust acoustic modes in collisional multicomponent plasmas

A comprehensive understanding of the physics underlying the dust-based processes and the ability to control the evolution of structures are essential in the field of plasma physics. This knowledge provides the foundation for numerous advanced scientific applications including the study of celestial objects and the synthesis of nanostructures. In this research, we consider the linear propagation of dust acoustic (DA) and dust ion acoustic (DIA) modes in a collisional plasma in the presence of an electron beam. The obtained dispersion relation demonstrates that the collision parameter and the electron beam density have significant contributions to the mode dynamics. The interactions of cold charged particles with neutrals result in a damping effect in the mode dynamics, which subsequently leads to a typical cutoff in the propagation of dust acoustic modes. Furthermore, the electron beam density can control the damping rate at different conditions. An increase in the electron beam density results in an acceleration of the DA mode damping, while the effect on the DIA mode is the opposite. The influence of the electron beam on the dynamics of the modes is more pronounced in the presence of strong collisions. Our analysis also shows that the propagation dynamics of each mode is strongly related to the wave vector. The damping rate is more pronounced in small wave vectors. Numerical analysis indicates that mode propagation can be controlled by the collision parameters and electron beam density. Furthermore, as a general trend, increasing the wave vector causes a shift in the cutoff toward higher collisions.

Dynamic Kohn anomaly in twisted bilayer graphene

Abstract Twisted bilayer graphene (TBG) has attracted great interest in the last decade due to the novel properties it exhibited. It was revealed that e–phonon interaction plays an important role in a variety of phenomena in this system, such as superconductivity and exotic phases. However, due to its complexity, the e–phonon interaction in TBG is not well studied yet. In this work, we study the electron interaction with the acoustic phonon mode in TBG and one of its consequences, i.e. the Kohn anomaly. The Kohn anomaly in ordinary metals usually happens at phonon momentum q = 2 k F as a dramatic modification of the phonon frequency when the phonon wave vector nests the electron Fermi surface. However, novel Kohn anomaly can happen in topological semimetals, such as graphene and Weyl semimetals. In this work, we show that the novel dynamic Kohn anomaly can also take place in TBG due to the nesting of two different Moire Dirac points by the phonon wave vector. Moreover, by tuning the twist angle, the dynamic Kohn anomaly in TBG shows different features. Particularly, at magic angle when the electron bandwidth is almost flat, the dynamic Kohn anomalies of acoustic phonons disappear. We also studied the effects of finite temperature and doping on the dynamic Kohn anomaly in TBG and discussed the experimental methods to observe the Kohn anomaly in such system.

Rotating nonlinear states in trapped binary Bose–Einstein condensates under the action of the spin–orbit coupling

Abstract We report results of systematic analysis of confined steadily rotating patterns in the two-component BEC including the spin–orbit coupling (SOC) of the Rashba type, which acts in the interplay with the attractive or repulsive intra-component and inter-component nonlinear interactions and confining potential. The analysis is based on the system of the Gross–Pitaevskii equations (GPEs) written in the rotating coordinates. The resulting GPE system includes effective Zeeman splitting. In the case of the attractive nonlinearity, the analysis, performed by means of the imaginary-time simulations, produces deformation of the known two-dimensional SOC solitons (semi-vortices and mixed-modes). Essentially novel findings are reported in the case of the repulsive nonlinearity. They demonstrate patterns arranged as chains of unitary vortices which, at smaller values of the rotation velocity Ω, assume the straight (single-string) form. At larger Ω, the straight chains become unstable, being spontaneously replaced by a trilete star-shaped array of vortices. At still larger values of Ω, the trilete pattern rebuilds itself into a star-shaped one formed of five and, then, seven strings. The transitions between the different patterns are accounted for by comparison of their energy. It is shown that the straight chains of vortices, which form the star-shaped structures, are aligned with boundaries between domains populated by plane waves with different wave vectors. A transition from an axisymmetric higher-order (multiple) vortex state to the trilete pattern is investigated too.

One-dimension periodic potentials in Schrödinger equation solved by the finite difference method

Abstract The one-dimensional Kronig–Penney (KP) potential in the Schrödinger equation, a standard periodic potential in quantum mechanics textbooks known for generating band structures, is solved by using the finite difference method (FDM) with periodic boundary conditions. This method significantly improves the eigenvalue's accuracy compared to existing approaches such as the filter method. The effects of the width and height of the KP potential on the eigenvalues and wave functions are then analyzed. As the potential height increases, the variation of eigenvalues with the wave vector slows down. Additionally, for higher-order band structures, the magnitude of the eigenvalue significantly decreases with increasing potential width. Finally, the Dirac comb potential, a periodic δ potential, is examined using the present framework. This potential corresponds to the KP potential's width and height approaching zero and infinity, respectively. The numerical results obtained by the FDM for the Dirac comb potential are also perfectly consistent with the analytical solution.

Exploration of quantum oscillation in antiferromagnetic Weyl semimetal GdSiAl

GdSiAl single crystal has been investigated by means of magnetic and magneto-transport measurements and compared withab-initiodensity functional theory (DFT) calculations. Significant non-saturating magnetoresistance reaching∼18%at 12T and2Kwas observed, alongside the presence of Shubnikov-de Haas oscillations with the fundamental frequencies 22.09T and 77.33T. Shubnikov-de Haas oscillations provide the information about the nontrivialπBerry phase in GdSiAl with the Fermi surface areas of0.00211A˚-2and0.00739A˚-2. Angle-dependent magnetoresistance shows anisotropy withθ, exhibiting a maximum at 180°. The magnetic susceptibility data forH∥candH⊥creveals that the magnetic moments of Gd3+ions orders antiferromagnetically below 32K along with an another transition occurs at∼8K, which is consistent with the heat capacity measurements where a distinctλ-shaped anomaly has been observed near antiferromagnetic ordering temperature 32K. The high value of Debye temperature indicates the contribution of acoustic phonons. Electronic structure calculations suggest the existence of nested Fermi surface pockets characterized by nesting wave vectors that closely align with the observed magnetic ordering wave vector. Furthermore, DFT calculations reveal the presence of Weyl nodes in close proximity to the Fermi surface. Our findings from combined experimental and theoretical techniques indicate GdSiAl to be a potential candidate for an antiferromagnetic topological Weyl semimetal.

Thermal quantum coherence: a comparative study of molybdenum disulfide versus graphene

Abstract This study examines quantum coherence in molybdenum disulfide $MoS_2$ by considering thermal fluctuations and the spin-orbit coupling of molybdenum's $d$ orbitals. Our results reveal that at the ground state, the system exhibits significant coherence, particularly for high values of the wave vector $k$. Interestingly, this coherence improves with increasing temperature before asymptotically decreasing towards zero. In conclusion, we have shown that graphene generally outperforms molybdenum due to its perfect two-dimensional structure thanks to the high mobility of electrons in its conduction bands. Moreover, these findings enable predictions about the behavior of other materials with similar band structures based on their crystal lattice interactions.

The effect of in-plane wave vector and heterostructure strain on spin-transport properties in ZnO/ZnCdO heterostructure

The effect of in-plane wave vector and heterostructure strain on spin-transport properties in ZnO/ZnCdO heterostructure

Strong Coupling between Moiré-Type Plasmons and Phonons in Suspended Monolayer Metallic Twisted Superlattices.

We demonstrate both experimentally and analytically a strong coupling phenomenon between moiré-type plasmons and phonons within moiré superlattices. We study the dependence of moiré wave vector and the twist angle and numerically simulate and experimentally fabricate metallic moiré superlattices on a suspended thin film SiO2 substrate at different twist angles. The results suggest that the coupling strength initially increases and then decreases with increasing twist angles. When the twist angle is at 16.26°, we achieve a moiré-type plasmon-phonon strong coupling with a Rabi splitting strength approaching 45 meV. We further analyze the coupling system by utilizing the coupled-harmonic-oscillators theory and quantum mechanical theory. The calculations and numerical simulations further agree with the experimental results. The proposed strong coupling system has the potential to contribute substantially to electromagnetic field controlling and coupling.

Wave Interaction in Two Species Ion-implanted Semi-conductor Plasma

The present paper is aimed to report the analytical study of wave interaction in two species (InSb, GaAs) ion implanted semiconductor plasma. Considering that the third order optical susceptibility χᶟ arising from the nonlinear wave interaction and using couple mode theory an analytical investigation of two species with ion-implantation has been presented. We have studied the threshold (E0th) and gain characteristics (α) with number density (n0) and wave vector (k) respectively. It can be seen that, in the case of GaAs shows a favourable enhancement in steady-state as well as the gain coefficient of the generated acoustic mode.

Predicting spatial curvature ΩK in globally CPT -symmetric universes

Boyle and Turok’s CPT-symmetric universe model posits that the Universe was symmetric at the big bang, addressing numerous problems in both cosmology and the Standard Model of particle physics. We extend this model by incorporating the symmetric conditions at the end of the Universe, which impose constraints on the allowed perturbation modes. These constrained modes conflict with the integer wave vectors required by the global spatial geometry in a closed universe. To resolve this conflict, only specific values of curvature are permissible, and in particular the curvature density is constrained to be ΩK∈{−0.016,−0.011,−0.004,…}, consistent with observations. Published by the American Physical Society 2024

Noncollinear Magnetic Structures in the Chiral Antiperovskite β-Fe2SeO.

We present the magnetic properties of the chiral, polar, and possibly magnetoelectric antiperovskite β-Fe2SeO as derived from magnetization and specific-heat measurements as well as from powder neutron diffraction and Mössbauer experiments. Our macroscopic data unambiguously reveal two magnetic phase transitions at TN1 ≈ 103 K and TN2 ≈ 78 K, while Rietveld analysis of neutron powder diffraction data reveals a noncollinear antiferromagnetic structure featuring magnetic moments in the a-b plane of the trigonal structure and a ferromagnetic moment along c. The latter is allowed by symmetry between TN1 and TN2, weakly visible in the magnetization data yet unresolvable microscopically. While the intermediate phase can be expressed in the trigonal magnetic space group P31, the magnetic ground state is modulated by a propagation vector q = (1/2 1/2 0) resulting in triclinic symmetry and an even more complex low-temperature spin arrangement which is also reflected in the Mössbauer hyperfine patterns indicating additional splitting of Fe sites below TN2. The complex noncollinear spin arrangements suggest interesting magnetoelectric properties of this polar magnet.

Optical excitation and detection of high-frequency Sezawa modes in Si/SiO2 system decorated with Ni80Fe20 nanodot arrays

Surface acoustic waves have emerged as one of the potential candidates for the development of next-generation wave-based information and computing technologies. For practical devices, it is essential to develop the excitation techniques for different types of surface acoustic waves, especially at higher microwave frequencies, and to tailor their frequency versus wave vector characteristics. We show that this can be done by using ultrashort laser pulses incident on the surface of a multilayer decorated with a periodic array of metallic nanodots. Specifically, we study surface acoustic waves in the dielectric substrate Si/SiO2 decorated with a square lattice of thin Ni80Fe20 (Py) dots. Using a femtosecond laser-based optical pump–probe measurement, we detect a number of high-frequency phononic modes. By performing finite element simulations, we identify them as Sezawa modes from the second and third Brillouin zone in addition to the modes confined within the Py dots. The frequency of the Sezawa modes strongly depends on the period of the Py dots and varies in the range between 5 to 15 GHz. Both types of waves cover the same frequency range for Py dots with period less than 400 nm, providing a promising system for magnetoelastic studies.

Occurrence of Grapevine Viruses in Different Cultivars and Regions Within Michigan

Viral diseases are widespread in vineyards throughout the world. Vineyard viruses are mostly disseminated via vegetative propagation, although insect and nematode vectors can also be involved in the spread. Michigan faces challenges with grapevine viruses due to the following: 1) multiple Vitis sp. (Vitis vinifera, Vitis labrusca, and Vitis interspecific hybrids) being cultivated within the state, 2) vineyards that vary in age, and 3) plant material being sourced from a variety of locations throughout the United States. Determining the distribution of grapevine viruses in Michigan is the first step in developing mitigation strategies. In this study we utilized real-time RT-PCR to test for a variety of grapevine viruses that are known to occur in other regions. Vineyards were sampled for grapevine leaf tissue (n = 429) across the northwest, southwest, mid, and southeast regions of the lower peninsula of Michigan and screened for a panel of viruses. Across all samples, grapevine rupestris stem pitting-associated virus (GRSPaV) was the most abundant. Other viruses found in relatively high abundance included grapevine leafroll-associated virus 3 (GLRaV3), grapevine fleck virus (GFkV), and tobacco ringspot virus (TRSV). Interestingly, this study identified grapevine red blotch virus (GRBV) and grapevine Pinot gris virus (GPGV), for the first time within the state. This survey gives researchers and growers an awareness of the distribution of viruses in Michigan vineyards that can aid management recommendations and encourage the use of virus tested material from reputable sources when planting new vineyards.

Biaxial Gaussian Beams, Hermite–Gaussian Beams, and Laguerre–Gaussian Vortex Beams in Isotropy-Broken Materials

We have developed the paraxial approximation for electromagnetic fields in arbitrary isotropy-broken media in terms of the ray–wave tilt and the curvature of materials’ Fresnel wave surfaces. We have obtained solutions of the paraxial equation in the form of biaxial Gaussian beams, which is a novel class of electromagnetic field distributions in generic isotropy-broken materials. Such beams have been previously observed experimentally and numerically in hyperbolic metamaterials but have evaded theoretical analysis in the literature up to now. Biaxial Gaussian beams have two axes: one in the direction of the Abraham momentum, corresponding to the ray propagation, and another in the direction of the Minkowski momentum, corresponding to the wave propagation, in agreement with the recent theory of refraction, ray–wave tilt, and hidden momentum [Durach, 2024]. We show that the curvature of the wavefronts in the biaxial Gaussian beams correspond to the curvature of the Fresnel wave surface at the central wave vector of the beam. We obtain the higher-order modes of the biaxial beams, including the biaxial Hermite–Gaussian and Laguerre–Gaussian vortex beams, which opens avenues toward studies of the optical angular momentum (OAM) in isotropy-broken media, including generic anisotropic and bianisotropic materials.

Wave turbulence in a rotating channel: numerical implementation and results

The analysis of Scott (J. Fluid Mech., vol. 741, 2014, pp. 316–349) is implemented numerically. Decaying turbulence is confined to a channel between two infinite, parallel, rotating walls. The Rossby and Ekman numbers are supposed small, the former condition making nonlinearity small, while the latter allows the turbulence to persist for the many rotational periods needed for the small nonlinearity to be effective. The flow is expressed as a combination of inertial waveguide modes, indexed by a two-dimensional wave vector $\boldsymbol{k}$ and an integer n. The $n = 0$ modes form a two-dimensional component of the flow, whereas the remainder is the wave component, on which attention is focused in this article. Assuming statistical axisymmetry and homogeneity in directions parallel to the walls, the second-order moments of the mode amplitudes yield a spectral matrix ${A_{nm}}(k,t)$ (where $k = |\boldsymbol{k} |$ ), of which the diagonal elements describe the distribution of energy over different modes. Wave-turbulence analysis provides an equation governing the time evolution of ${A_{nn}}$ , $n \ne 0$ , the wave spectra, which forms the basis for the present work. The initial distribution of energy is Gaussian and depends on a parameter $\varXi$ , the initial spectral width. The problem has two other parameters, ${\beta _w}$ and ${\beta _v}$ , which correspond to two distinct viscous dissipative mechanisms: wall damping due to boundary layers and volumetric damping by viscous effects throughout the flow. Results obtained by numerical solution include the time evolution of the total wave energy, E, and the detailed description of its distribution over k and n provided by ${A_{nn}}(k)$ .

Abstract 4137246: Atrial Fibrillation Wave Vectors Determined by Artificial-Intelligence Indicate Clinical Phenotypes

Background: Atrial fibrillation (AF) is a major cause of morbidity and mortality, which may be reduced by ablation. However, it is difficult to predict patients who will respond, which is currently done using bedside variables since even experts find it difficult to interpret electrical signals (electrograms) or maps in AF, or link them with phenotype, acute or long-term ablation response. Hypothesis: We hypothesized that determining if AF waves consistently propagate away from the pulmonary veins (PV), identified using artificial-intelligence (AI) tools applied to spatial grids in multipolar catheters, may reflect phenotypes of response to ablation or other clinical features. Methods: We studied 26,640 electrograms in N=37 patients at AF ablation ( 66.3 ± 8.6 years, 13.5% women, 59.5% non-paroxysmal AF). We trained AI-algorithms to identify activation patterns and calculate propagation vectors in AF. Each patient had AF recordings from 64-pole basket catheters, from which we calculated AI-based vectors in 48 spatial grids of 3X3 electrodes (covering ~1-3 cm 2 ) over 1 minute (720 per patient). Fig. A illustrates AF waves predominantly exiting the PVs in a 60 year old man. We studied wave maps exiting the PVs in relation to AF type, termination of AF during ablation and 1 year outcome. Results: Ablation success for the cohort was 71.4% at 1 year. Wave direction in AF shifted over time, as expected, but predominant vectors correlated with clinical outcomes. Fig. B showed that AF waves were significantly more likely to exit the PVs for patients with success than failed ablation (<0.05). Fig. C showed that PV wave direction did not differ for AF type, nor for patients with or without acute AF termination by ablation (p=NS). Conclusions: In this study of patients with various types of AF, a novel AI-based approach showed that AF vectors indicating waves exiting the PVs predicted , clinical phenotypes, particularly patients with successful ablation targeting the PVs.

Superconductivity and strain-enhanced phase stability of Janus tungsten chalcogenide hydride monolayers

Janus transition metal-dichalcogenide materials have attracted a great deal of attention due to their remarkable physical properties arising from the two-dimensional geometry and the breakdown of the out-of-plane symmetry. Using first-principles density functional theory, we investigated the phase stability, strain-enhanced phase stability, and superconductivity of Janus WSeH and WSH. In addition, we investigated the contribution of the phonon linewidths from the phonon energy spectrum responsible for the superconductivity and the electron-phonon coupling as a function of phonon wave vectors and modes. Previous work has examined hexagonal 2H and tetragonal 1T structures, but we found that neither is a ground-state structure. The metastable 2H phase of WSeH is dynamically stable with Tc≈11.60K, similar to WSH. Compressive biaxial strain—the two-dimensional equivalent of pressure—can stabilize the 1T structures of WSeH and WSH with Tc≈9.23K and 10.52 K, respectively. Published by the American Physical Society 2024

Highly efficient single photon coupling via surface plasmons into single-mode optical fiber

Quanta of light (single photon) play as one of the building blocks of photonic based quantum computations, sensing, and communications. This makes a necessity to develop practical approaches for tuning, guiding, and coupling of single photons in photonic circuits for viable applications. Interaction and coupling efficiency of single photon into optical fibers is a technical bottleneck of quantum optics and should be addressed by novel design and materials. Here, we introduce a fiber-based micro-photonic design to directly coupling of the emitted single-photon to the core of a single mode fiber (SMF). The results of the simulation indicate that the emission of single photon source on a D-shaped SMF coated by a thin plasmonic film, provide remarkable amplifying of the evanescent field by confined surface plasmons into the SMF. The numerical analysis of different types and thicknesses of plasmonic materials by finite element method (FEM) is conducted to study the propagation vectors along the SMF as a function of the emission angle and wavelength of the single photon source. The results revealed that by the optimum thickness of the tantalum layer as novel plasmonic material, the best record of coupling efficiency can be achieved in the fiber optics communication region (λ ∼ 1550 nm). This approach sheds light on novel plasmonic-assisted coupling and promises a functional strategy for single photon manipulation in various fields of quantum optics.

Effects of Lu-doping on the magnetic behaviour and ordering of (Ho[formula omitted]Lu[formula omitted])2Fe2Si2C

We have investigated the effects of Lu substitution on the magnetic behaviour and ordering of (Ho1−xLux)2Fe2Si2C (x = 0.32 and 0.46) by high-resolution neutron powder diffraction, magnetisation and specific heat over the temperature range 2 to 300 K. Our study has established that the antiferromagnetic (AFM) state is weakened upon Lu substitution and that the Néel temperature TN shifts towards lower temperature with increasing Lu content. The replacement of the magnetic Ho3+ ion by the non-magnetic Lu3+ ion of smaller atomic radius, leads to a modification of the crystal field levels, as indicated by the specific heat measurements. Neutron diffraction data analysis reveals that the magnetic structure of undoped Ho2Fe2Si2C, which exhibits a commensurate, antiferromagnetic ordering of the Ho sublattice along the b-axis with a propagation vector k = [0, 0, 12], is maintained in the Lu-doped (Ho1−xLux)2Fe2Si2C compounds.

Topological magnon in exchange frustration driven incommensurate spin spiral of kagome-lattice YMn6Sn6

YMn6Sn6 consists of two types of Mn-based kagome planes stacked along the c-axis having a complex magnetic interaction. We report a spin reconstruction in YMn6Sn6 from ferromagnetic (FM) into a combination of two incommensurate spin spirals (SSs) originating from two different types of Mn kagome planes driven by frustrated magnetic exchanges along the c-axis with the inclusion of the Hubbard U. The pitch angle and wave vector of the incommensurate SSs are ∼89.3∘ and ∼ (0 0 0.248), respectively, which are in excellent agreement with the experiment. We employ an effective model Hamiltonian constructed out of exchange interactions to capture the experimentally observed nonequivalent nature of the two incommensurate SSs which also explain the FM-SS crossover due to antiferromagntic spin exchange with correlation. We further report the existence of a topological magnon with spin-orbit coupling in the incommensurate SS phase of YMn6Sn6 by calculating the topological invariants and Berry curvature profile. The location of the Dirac magnon in the energy landscape at 73 meV matches with another experimental report. We demonstrate the accuracy of our results by highlighting the experimental features in YMn6Sn6. Published by the American Physical Society 2024