Multipole Response Research Articles

Majorana multipole response with magnetic point group symmetry

Majorana multipole response with magnetic point group symmetry

Anisotropic magnetic and quadrupolar H−T phase diagram of CeRh2As2

The tetragonal heavy-fermion compound CeRh2As2 has intriguing low-temperature symmetry-breaking phases whose nature is unclear. The unconventional superconducting phase is complemented by other normal-state phases which presumably involve ordering of 4f electron multipoles supported by the Kramers doublets split by the tetragonal crystal electric field (CEF). The most striking aspect is the pronounced anisotropic H−T phase boundary for in-plane and out-of plane field directions. Using a localized 4f CEF model we demonstrate that its essential features can be understood as the result of competing low-field easy-plane magnetic order and field-induced quadrupolar order of xy type. We present calculations based on coupled multipole random phase approximation response function approach as well as molecular field treatment in the ordered regime. We use an analytical approach for a reduced quasiquartet model and numerical calculations for the complete CEF level scheme. We discuss the quantum critical properties as function of multipolar control parameters and explain the origin of a pronounced ac anisotropy of the H−T phase diagram. Finally, the field and temperature evolution of multipolar order parameters is derived and the high-field phase diagram is predicted. Published by the American Physical Society 2024

Underwater low frequency subwoofer systems

Experiments with a gas-filled adiabatic bubble resonator of large diameter have shown that it is an efficient emitter of low-frequency seismic waves. The resonator has a single resonant frequency with a narrow bandwidth. The internal acoustic resonant structure changes the frequency response of the entire source and makes it possible to expand its bandwidth. An internal Helmholtz resonator converts the system into a double resonant system with a wide bandwidth. The bass-reflex resonator separates the pressure in front and behind the speaker cone, and the speaker works as an internal monopole driver. Any other known loudspeaker enclosure design can be used to create the desired multi-pole frequency response. A specific of the underwater enclosure is that it is loaded into the inner chamber of the bubble resonator. The bubble resonator works as an efficient impedance converter, matching the impedance of the internal resonant system to the water radiation impedance. Examples of various systems and the results of their tests in water are considered. Experiments have shown that a gas-filled underwater bubble covered with an elastic membrane and driven by an audio subwoofer can achieve source levels of 180–185 dB re 1 μPa@1 m over a wide frequency band.

Implementation of the quasiparticle finite amplitude method within the relativistic self-consistent mean-field framework (II): The program DIRQFAM v2.0.0

We describe the new version 2.0.0 of the code DIRQFAM that calculates the multipole response of even-even axially symmetric deformed nuclei using the framework of relativistic self-consistent mean-field models. The response is calculated by implementing the finite amplitude method for relativistic quasiparticle random phase approximation. In the new version, we have implemented the following features: (i) meson-exchange interactions, (ii) low-rank method for calculating induced densities and currents, (iii) generalized minimal residual method (GMRES), (iv) evaluation of the nucleon localization function, (v) extraction of the QRPA transition matrix elements and eigenfrequencies, (vi) evaluation of the H11 part of the induced Hamiltonian, (vii) multipole excitation operators up to J≤5 are now included. Program summaryProgram title:DIRQFAM v2.0.0CPC Library link to program files:https://doi.org/10.17632/6gv8nxg4ns.2Licensing provisions: GPLv3Programming language: Fortran 90.External routines/libraries: BLAS/LAPACK, version 3.1. or higher.Journal reference of previous version: A. Bjelčić, T. Nikšić, Comp. Phys. Comm. 253, 107184 (2020).Does the new version supersede the previous version?: YesNature of problem: Multipole response of deformed even-even open-shell nuclei can be calculated using the quasiparticle finite amplitude method (QFAM), based on the relativistic self-consistent mean-field models. The particle-hole channel is described by a zero-range relativistic effective interaction or interaction based on meson exchange, while the particle-particle channel of the effective inter-nucleon interaction is described by a separable finite-range pairing force. The method can be applied to perform systematic studies of collective modes even in heavy deformed nuclei.Solution method: The current implementation computes the multipole response by solving the QFAM equations in a self-consistent iteration scheme. At each iteration the QFAM solutions are updated using the GMRES method. The QFAM amplitudes are expanded in the simplex-y harmonic oscillator basis.Summary of revisions:1.meson-exchange interaction are included in the code;2.calculation of the nucleon localization function;3.extraction of the QRPA transition matrix elements and eigenfrequencies;4.evaluation of the H11 part of the induced Hamiltonian;5.multipoles excitation operators up to J≤5 are included;6.low-rank method for calculating induced densities and currents;7.generalized minimal residual method;8.dynamic memory allocation;9.reduced memory requirements;Additional comments including restrictions and unusual features: Open-shell even-even nuclei with parity conserved axially symmetric ground states are considered. An electric multipole operator with J≤5 is used to calculate the response function.

Active optical modulation of quasi-BICs in Si-VO2 hybrid metasurfaces.

Active optical modulation breaks the limitation of a passive device, providing a new, to the best of our knowledge, alternative to achieve high-performance optical devices. The phase-change material vanadium dioxide (VO2) plays an important role in the active device due to its unique reversible phase transition. In this work, we numerically investigate the optical modulation in resonant Si-VO2 hybrid metasurfaces. The optical bound states in the continuum (BICs) in an Si dimer nanobar metasurface are studied. The quasi-BICs resonator with high quality factor (Q-factor) can be excited by rotating one of the dimer nanobars. The multipole response and near-field distribution confirm that magnetic dipoles dominate this resonance. Moreover, a dynamically tunable optical resonance is achieved by integrating a VO2 thin film to this quasi-BICs Si nanostructure. With the increase of temperature, VO2 gradually changes from the dielectric state to metal state, and the optical response exhibits a significant change. Then, the modulation of the transmission spectrum is calculated. Situations where VO2 is located in different positions are also discussed. A relative transmission modulation of 180% is achieved. These results fully confirm that the VO2 film shows an excellent ability to modulate the quasi-BICs resonator. Our work provides a route for the active modulation of resonant optical devices.

Chebyshev kernel polynomial method for efficient calculation of the quasiparticle random phase approximation response function

Efficient and accurate algorithms for the calculation of the multipole response of deformed atomic nuclei are very important tools in nuclear structure, especially for large scale calculations. In this paper we present an implementation of the algorithm based on the expansion of the response function in terms of the Chebyshev polynomials in conjunction with the kernel polynomial method for a very efficient calculation of the quasiparticle random phase approximation response function. Several test calculations are performed in order to asses the applicability and feasibility of this algorithm, already used successfully in the field of computational solid state physics, in various nuclear structure calculations.

Magnetoelectric Classification of Skyrmions.

We develop a general theory to classify magnetic skyrmions and related spin textures in terms of their magnetoelectric multipoles. Since magnetic skyrmions are now established in insulating materials, where the magnetoelectric multipoles govern the linear magnetoelectric response, our classification provides a recipe for manipulating the magnetic properties of skyrmions using applied electric fields. We apply our formalism to skyrmions and antiskyrmions of different helicities, as well as to magnetic bimerons, which are topologically, but not geometrically, equivalent to skyrmions. We show that the nonzero components of the magnetoelectric multipole and magnetoelectric response tensors are uniquely determined by the topology, helicity, and geometry of the spin texture. Therefore, we propose straightforward linear magnetoelectric response measurements as an alternative to Lorentz microscopy for characterizing insulating skyrmionic textures.

Multipole Response of Ni and Sn Isotopes and its Momentum Dependence

We have used a self-consistent Skyrme-HF plus Continuum RPA model to study the low-multipole response of stable and neutron/proton-rich Ni and Sn isotopes using suitable Skyrme parametrizations. Experimental studies of these nuclei are being planned at RIKEN. We focus on the momentum dependence of the strength distribution, as it may provide information on the structure of excited nuclear states.

Majorana multipole response: General theory and application to wallpaper groups

Whereas identification of Cooper-pair symmetry is the first and crucial step in the investigation of unconventional superconductors, only a few have been established so far because of their own difficulties. To solve this problem, we develop a theory for identification of pairing symmetry using knowledge of topological superconductivity. Establishing the multipole theory of emergent Majorana fermions in time-reversal-invariant topological superconductors, we discover a one-to-one correspondence between the electromagnetic response of Majorana fermions and Cooper-pair symmetry. The emergent Majorana fermions host magnetic structures that share the same irreducible representation with Cooper pairs under crystalline symmetry. We furthermore reveal that Majorana fermions in high-spin or nonsymmorphic superconductors may exhibit magnetic octupole responses, which give a direct evidence of these exotic superconducting states. Electric responses of multiple Majorana Kramers pairs are also clarified. Our theory provides the fundamentals for identification of unconventional Cooper pairings through surface-spin-sensitive measurements as well as that for manipulation of Majorana fermions by external electromagnetic fields.

Optical coupling of overlapping nanopillars

Engineering of nanophotonic devices for controlling light requires deep understanding of the interaction between their subwavelength structure elements. Theoretical approaches based on the multiple scattering theory provide simple analytics valuable for design. However, they consider different elements separated by the surrounding medium. Here, we develop an approach to study wave coupling in the case of overlapping particles. We consider the simplest system-a dimer of nanopillars-and find that it can be described by a three-oscillator model. Two modes correspond to the multipole response of isolated particles that interact through radiating and evanescent waves in accordance with the conventional multiple scattering theory, but there exists a third effective non-resonant oscillator supporting a direct mode coupling via the intersecting part. Our simple model yields results with a reliable agreement with numerical simulations and allows insight into the physical processes underlying the collective response of a cluster of overlapped subwavelength particles.

Tunable microwave-photonic filtering with high out-of-band rejection in silicon

The ever-increasing demand for high speed and large bandwidth has made photonic systems a leading candidate for the next generation of telecommunication and radar technologies. The photonic platform enables high performance while maintaining a small footprint and provides a natural interface with fiber optics for signal transmission. However, producing sharp, narrow-band filters that are competitive with RF components has remained challenging. In this paper, we demonstrate all-silicon RF-photonic multi-pole filters with ∼100× higher spectral resolution than previously possible in silicon photonics. This enhanced performance is achieved utilizing engineered Brillouin interactions to access long-lived phonons, greatly extending the available coherence times in silicon. This Brillouin-based optomechanical system enables ultra-narrow (3.5 MHz) multi-pole response that can be tuned over a wide (∼10 GHz) spectral band. We accomplish this in an all-silicon optomechanical waveguide system, using CMOS-compatible fabrication techniques. In addition to bringing greatly enhanced performance to silicon photonics, we demonstrate reliability and robustness, necessary to transition silicon-based optomechanical technologies from the scientific bench-top to high-impact field-deployable technologies.

Shaping nonlinear optical response using nonlocal forward Brillouin interactions

In most practical scenarios, optical susceptibilities can be treated as a local property of a medium. For example, in the context of nonlinear optics we can typically treat the Kerr and Raman response as local, such that optical fields at one location do not produce a nonlinear response at distinct locations in space. This is because the electronic and vibrational disturbances produced within the material are confined to a region that is smaller than an optical wavelength. By comparison, Brillouin interactions, mediated by traveling-wave acoustic phonons, can result in a highly nonlocal nonlinear response as the elastic waves generated in the process can occupy a region in space much larger than an optical wavelength. The unique properties of these interactions can be exploited to engineer new types of processes, where highly delocalized phonon modes serve as an engineerable channel that mediates scattering processes between light waves propagating in distinct optical waveguides. These types of nonlocal optomechanical responses have recently been demonstrated as the basis for information transduction, however the nontrivial dynamics of such systems has yet to be explored. In this work, we show that the third-order nonlinear process resulting from spatially extended Brillouin-active phonon modes involves mixing products from spatially separated, optically decoupled waveguides, yielding a nonlocal susceptibility. Building on these concepts, we illustrate how nontrivial multi-mode acoustic interference can produce a nonlocal susceptibility with a multi-pole frequency response, as the basis for new optical and microwave signal processing schemes within traveling wave systems.

Implementation of the quasiparticle finite amplitude method within the relativistic self-consistent mean-field framework: The program DIRQFAM

The DIRQFAM code calculates the multipole response of even–even axially symmetric deformed nuclei using the framework of relativistic self-consistent mean-field models. The response is calculated by implementing the finite amplitude method for relativistic quasiparticle random phase approximation. Program summaryProgram Title:DIRQFAMProgram Files doi:http://dx.doi.org/10.17632/6gv8nxg4ns.1Licensing provisions: GPLv3Programming language: Fortran 90/95, easily downgradable to FORTRAN 77.External routines/libraries: BLAS/LAPACK, version 3.6.0. or higher.Nature of problem: Multipole response of deformed even–even open-shell nuclei can be calculated using the quasiparticle finite amplitude method (QFAM), based on the relativistic self-consistent mean-field models. The particle–hole channel is described by a zero-range relativistic effective interaction, while the particle–particle channel of the effective inter-nucleon interaction is described by a separable finite-range pairing force. The method can be applied to perform systematic studies of collective modes even in heavy deformed nuclei.Solution method: The current implementation computes the multipole response by solving the QFAM equations in a self-consistent iteration scheme. At each iteration the QFAM solutions are updated using the modified Broyden’s method. The QFAM amplitudes are expanded in the simplex-y harmonic oscillator basis.Restrictions: Open-shell even–even nuclei with axially symmetric ground states are considered. An electric multipole operator with J≤3 is used to calculate the response function.Unusual features: The code should be recompiled before running it with different values of one of the following input parameters: number of oscillator shells in the expansion of nucleon spinors (n0f), number of Gauss–Hermite (NGH) or Gauss–Laguerre nodes (NGL), the multipolarity values that define the external perturbation operator (J_multipole, K_multipole).

Majorana Multipole Response of Topological Superconductors.

In contrast to elementary Majorana particles, emergent Majorana fermions (MFs) in condensed-matter systems may have electromagnetic multipoles. We developed a general theory of magnetic multipoles for helical MFs on time-reversal-invariant superconductors. The results show that the multipole response is governed by crystal symmetry, and that a one-to-one correspondence exists between the symmetry of Cooper pairs and the representation of magnetic multipoles under crystal symmetry. The latter property provides a way to identify unconventional pairing symmetry via the magnetic response of helical MFs. We also find that most helical MFs exhibit a magnetic-dipole response, but those on superconductors with spin-3/2 electrons may display a magnetic-octupole response in leading order, which uniquely characterizes high-spin superconductors. Detection of such an octupole response provides direct evidence of high-spin superconductivity, such as in half-Heusler superconductors.

Broadband forward scattering from dielectric cubic nanoantenna in lossless media.

Dielectric photonics platform provides unique possibilities to control light scattering via utilizing high-index dielectric nanoantennas with peculiar optical signatures. Despite the intensively growing field of all-dielectric nanophotonics, it is still unclear how surrounding media affect scattering properties of a nanoantenna with complex multipole response. Here, we report on light scattering by a silicon cubic nanoparticle embedded in lossless media, supporting optical resonant response. We show that significant changes in the scattering process are governed by the electro-magnetic multipole resonances, which experience spectral red-shift and broadening over the whole visible and near-infrared spectra as the indices of media increase. Most interestingly, the considered nanoantenna exhibits the broadband forward scattering in the visible and near-infrared spectral ranges due to the Kerker-effect in high-index media. The revealed effect of broadband forward scattering is essential for highly demanding applications in which the influence of the media is crucial such as health-care, e.g., sensing, treatment efficiency monitoring, and diagnostics. In addition, the insights from this study are expected to pave the way toward engineering the nanophotonic systems including but not limited to Huygens-metasurfaces in media within a single framework.

Tunable circular dichroism of composite metamaterial on the basis of the phase transition of VO2

The circular dichroism (CD) effect characterized by different optical responses between left and right circularly polarized lights is widely applied for polarization-resolved detection and imaging. The tunable CD effect is of substantial importance in improving the detection sensitivity and imaging resolution. In this paper, we show that planar Z-shaped composite metamaterial embedded with VO2 that exhibits insulator-metal transition (IMT) can enable thermally tunable chirality. Simulated by the finite element method, the tunable CD effect can be achieved by changing the environment temperature to initiate the IMT of VO2. We also demonstrate that the underlying mechanism of the CD effect generation is the electric multipole oscillation response in the vicinity of the VO2 gap in vertical direction. These findings not only provide a new strategy to change chirality and tune the effect of CD dynamically but also broaden its potential applications in polarization-resolved detection and imaging.

Decomposition of scattered electromagnetic fields into vector spherical wave functions on surfaces with general shapes

Decomposing the field scattered by an object into vector spherical harmonics (VSH) is the prime task when discussing its optical properties on more analytical grounds. Thus far, it was frequently required in the decomposition that the scattered field is available on a spherical surface enclosing the scatterer; being with that adapted to the spatial dependency of the VSHs but being rather incompatible with many numerical solvers. To mitigate this problem, we propose an orthogonal expression for the decomposition that holds for any surface that encloses the scatterer, independently of its shape. We also show that the orthogonal relations remain unchanged when the radiative VSH used for the expansion of the scattered field are substituted by the VSH used for the expansion of the illumination as test functions. This is a key factor for the numerical stability of our decomposition. As example, we use a finite-element based solver to compute the multipole response of a nanorod illuminated by a plane wave and study its convergence properties.

Nuclear response at zero and finite temperature

We present some recent developments on the nuclear many-body problem, such as the treatment of high-order correlations and finite temperature in the description of in-medium two-nucleon propagators. In this work we discuss two-time propagators of the particle-hole type, which describe the response of finite nuclei to external probes without nucleon transfer. The general theory is formulated in terms of the equation of motion method for these propagators with the only input from the bare nucleon-nucleon interaction. The numerical implementation was performed on the basis of the effective mason-nucleon Lagrangian in order to study the energy-dependent kernels of different complexity. The finite-temperature extension of the theory with ph ⊗ phonon configurations is applied to a study of the multipole response of medium-mass nuclei.

Angular distribution of elastic scattering induced by F17 on medium-mass target nuclei at energies near the Coulomb barrier

The elastic scattering angular distributions were measured for 50- and 59-MeV F17 radioactive ion beam on a Y89 target. The aim of this work is to study the effect of the breakup of the proton halo projectile on the elastic scattering angular distribution. The experimental data were analyzed by means of the optical model with the double-folding São Paulo potential for both real and imaginary parts. The theoretical calculations reproduced the experimental data reasonably well. It is shown that the method of the data analysis is correct. In order to clarify the difference observed at large angles for the 59-MeV incident energy data, Continuum-Discretized Coupled-Channels (CDCC) calculations were performed to consider the breakup coupling effect. It is found that the experimental data show the Coulomb rainbow peak and that the effect of the coupling to the continuum states is not very significant, producing only a small hindrance of the Coulomb rainbow peak and a very small enhancement of the elastic scattering angular distribution at backward angles, suggesting that the multipole response of the neutron halo projectiles is stronger than that of the proton halo systems.2 MoreReceived 29 November 2017DOI:https://doi.org/10.1103/PhysRevC.97.044618©2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBreakup reactionsDirect reactionsLow & intermediate energy heavy-ion reactionsNucleon distributionUnstable nuclei induced nuclear reactionsProperties6 ≤ A ≤ 19TechniquesOptical, coupled-channel & distorted wave modelsNuclear Physics

High-Resolution Seafloor Absolute Pressure Gauge Measurements Using a Better Counting Method

AbstractVibrating quartz force transducers are the critical component of most deep-sea pressure and depth gauges in use in oceanography, producing a frequency output that varies with pressure. Accurate and low drift pressure measurements can be obtained by precisely measuring this frequency. In most implementations, the frequency is determined by counting the number of cycles of a high-frequency standard oscillator occurring during a large number of cycles of the lower-frequency quartz force oscillator. Resolution is limited by the sampling interval (length of counting) and the frequency of the frequency standard. Alternative counting methods can provide significant (20–40 dB) improvements in resolution at sampling rates above 1 Hz. Each counting method can be described as a different filter applied to the output of a counter of the frequency standard gated at each transition of the transducer quartz oscillator. Improvements in resolution can be understood as the result of minimizing the aliasing of higher-frequency counting noise into the spectrum below the Nyquist frequency. A simple multipole infinite impulse response (IIR) filter designed to limit spectral leakage of high-frequency noise minimizes the noise spectrum and thereby optimizes the resolution of the pressure output. The resultant noise spectrum rises as frequency squared above 1 Hz, independent of the sampling rate. At frequencies below 1 Hz, it is limited by noise in the electronics driving the force transducer quartz oscillator. Resolution increases with frequency of the frequency standard up to about 200 MHz, plateauing for higher frequencies due to other noise sources (likely electronic).