Gyrotropic Crystals Research Articles

Annealing effect of Ca3TaGa3Si2O14 catangasite crystals on their optical activity

The spectral dependences of transmission and absorption in the wavelength range of 200–2500 nm were measured for Ca3TaGa3Si2O14 crystals cut perpendicular to the optical axis in the initial state (without annealing) and after isothermal annealing in vacuum and in air. It was found that annealing in vacuum leads to a decrease, and annealing in air leads to an increase in the intensity of absorption bands. A spectrophotometric method for measuring and calculating the specific rotation angle ρ of the plane of polarization of light in gyrotropic crystals from the transmission coefficient spectra at different angles between the polarizer and the analyzer is considered. The transmission spectra were normalized in order to eliminate shifts in the spectra associated with measurement features. Spectral dependences of the values of ρ for all three samples, which are approximated by the extended Drude formula, are obtained; the influence of the annealing atmosphere on the values of the coefficients of this formula is established.

Axion topology in photonic crystal domain walls

Axion insulators are 3D magnetic topological insulators supporting hinge states and quantized magnetoelectric effects, recently proposed for detecting dark-matter axionic particles via their axionic excitations. Beyond theoretical interest, obtaining a photonic counterpart of axion insulators offers potential for advancing magnetically-tunable photonic devices and axion haloscopes based on axion-photon conversion. This work proposes an axionic 3D phase within a photonic setup. By building inversion-symmetric domain-walls in gyrotropic photonic crystals, we bind chiral modes on inversion-related hinges, ultimately leading to the realization of an axionic channel of light. These states propagate embedded in a 3D structure, thus protected from radiation in the continuum. Employing a small external gyromagnetic bias, we transition across different axionic mode configurations, enabling effective topological switching of chiral photonic fibers. While demonstrating the possibility of realizing axion photonic crystals within state-of-the-art gyrotropic setups, we propose a general scheme for rendering axion topology at domain walls of Weyl semimetals.

Determination of the Polarization Plane Specific Rotation in Gyrotropic Crystals of the Middle Category by the Spectrophotometric Method

Determination of the Polarization Plane Specific Rotation in Gyrotropic Crystals of the Middle Category by the Spectrophotometric Method

Gyrotropic Crystals as a Basis for Creation of Helical Polychromatic Singular Beams

In this work, studies are carried out in the field of optical singular beams that have passed through gyrotropic crystals. We have experimentally shown that singular beams with a helical intensity distribution are formed when passing through a system of two gyrotropic crystals with opposite values of the gyration coefficient. It is shown that the system is capable of generating optical vortices with a double topological charge in one of the components of circular polarization when light propagates through two gyrotropic crystals.

Determination of the polarization plane specific rotation in gyrotropic crystals of the middle category by the spectrophotometric method

A large number of modern functional single crystals of the middle category belong to gyrotropic media. In these crystals, when light propagates along the optical axis, rotation of the plane of its polarization is observed. In this work a spectrophotometric method was used to obtain the dispersion dependences of the rotation angle of the polarization plane. This method is based on measuring the intensity of light passing through the polarizer–crystal–analyzer system, the crystal is a polished plane-parallel plate of a uniaxial gyrotropic crystal cut perpendicular to the optical axis. Measurements were carried out on a UV-Vis-NIR spectrophotometer Cary-5000 in the wavelength range of 200—1200 nm using polarizers — Glan–Taylor prisms. Polished plane-parallel plates of known SiO2 and α-LiIO3 crystals were used as samples. The obtained dispersion dependences of the spectral transmission coefficients are oscillating. Discrete values of the specific angles of rotation of the plane of polarization of light are calculated from the extremes on these dependencies. These discrete values can be approximated by the formulas Drude, Chandrasekhar and Vyshina, depending on what determines the nature of the rotational ability of the plane of polarization of light in each particular material. For the studied crystals, dependences of the modified Drude formula of the form 1/ρ = f(λ2) are plotted, these dependences should have a linear character in the case of an ideal crystal. The obtained experimental results correlate well with the available literature data. The advantages of this method are efficiency, the possibility of obtaining dispersion dependences of the specific rotation angle of the polarization plane, the need for a single sample, the possibility of assessing the nature of the rotational ability of specific crystals, the possibility of evaluating the structural perfection of the studied crystals.

Orthogonal Two-Wave Vector Interaction in a Gyrotropic Photorefractive Crystal

Orthogonal Two-Wave Vector Interaction in a Gyrotropic Photorefractive Crystal

Surface waves Fabry-Perot modes of the finite magnetophotonic crystal in Voigt configuration

We have solved the problem of plane wave scattering by a finite gyrotropic magnetophotonic crystal in the Voigt configuration. To find an analytical solution, the method of the Floquet-Bloch wave theory with Cauchy boundary conditions for a one-dimensional magnetophotonic crystal and the transfer matrix method were used. The reflection and transmission coefficients are obtained in analytical form for arbitrary material parameters of the gyrotropic layers of the crystal. The field distributions within the finite crystal are found in explicit form. The regime of excitation of modified Zenneck-Sommerfeld waves and a new regime of unusual gyrotropic surface waves with positive values of the effective permittivity of one of the crystal layers are revealed. The features of the distribution of surface wave fields for the considered regimes of all Fabry–Perot modes at full transmission are studied. The nonreciprocal properties of the considered crystals are established depending on the incidence angle sign.

Laser Conoscopy of Two-Component Optical Systems from Gyrotropic Crystals

Laser Conoscopy of Two-Component Optical Systems from Gyrotropic Crystals

Practice of the Visual Determination of the Direction of the Rotation of the Light Polarization Plane in Gyrotropic Uniaxial Single Crystals

Practice of the Visual Determination of the Direction of the Rotation of the Light Polarization Plane in Gyrotropic Uniaxial Single Crystals

Practice of the visual determination of the direction of light polarization plane rotation in the gyrotropic uniaxial single crystals

When studying and applying crystals of the middle category, it is necessary to take into account the manifestations of anisotropy of their properties, in particular, optical anisotropy. One of the manifestations of optical anisotropy is the rotation of the polarization plane (gyrotropy effect), which is observed in the direction of the optical axis of such crystals. The plane of polarization of light can rotate clockwise and counterclockwise. To determine the direction of rotation of the polarization plane, simple visual methods can be used based on studies of samples in converging polarized light – observations of conoscopic figures. In general, the type of conoscopic figures depends on the relative position of the polarizers, the wavelength of light in the system, the cut of the single crystal perpendicular to which the light propagates, the thickness of the sample and the birefringence. The direction of rotation of the polarization plane can be determined by еру change of the type of conoscopic figure of a sample of a gyrotropic crystal cut perpendicular to the optical axis: change of the central spot color during the analyzer rotation; the extinction of the central spot when observing a conoscopic figure using light filters; the direction of movement of the rings in monochromatic light; observation of Airy patterns. According to the experience of working in our laboratory “Single crystals and Stocke on their Base”, the simplest, most operational and unambiguous visual method for determining the direction of rotation of the polarization plane is the observation of Airy figures. A conoscopic pattern in the form of Airy figures (a four-way spiral) occurs when observing in converging polarized light a combination of two superimposed samples of gyrotropic crystals cut perpendicular to the optical axis, rotating the plane of polarization of light in opposite directions. To use this method, a well-known sample of a gyrotropic crystal cut perpendicular to the optical axis is required.

Chiral Topological Surface States on a Finite Square Photonic Crystal Bounded by Air

Chiral, topologically protected, photonic surface states can be found at the boundary between gyrotropic photonic crystals where a changing magnetic field induces different topology across the interface. Typically, photonic crystals with either a suitable band structure on both sides of the interface to provide a band gap and evanescent decay of the surface states away from the interface, or an outer layer with engineered material properties is required. In this paper, we show the emergence of topological, unidirectional surface states at the termination of finite gyrotropic photonic crystals with a simple square lattice and ${\mathcal{C}}_{4}$ rotational symmetry bounded by a vacuum, eliminating the need for an outside layer to enable chiral surface modes. We start from an infinite, time-reversal-symmetry-breaking photonic crystal with a band gap associated with bands with nonzero Chern numbers, different from all-zero Chern numbers in air. We then modify the photonic crystal to move this band gap below the light line, while maintaining the Chern-number discontinuities. Band-structure calculations for a supercell approximating a photonic crystal finite in the direction normal to the surface demonstrate the existence, dispersion, and chirality of the surface mode. Extensive direct scattering calculations for a point source and spatial Fourier analysis further reveal a unidirectional free-space topological surface state, which propagates counterclockwise around the surface of a finite photonic crystal, providing a nearly foolproof way to cross-check the surface-mode band structure unaffected by backscattering from local defects. Additionally, scattering simulations allow an independent characterization of the state dispersion and unveil the robustness of the topological plasmonic mode propagation around the ${90}^{\ensuremath{\circ}}$ bends of the structure, being due to only radiation leakage. In contrast to buried topological surface states, the observed surface modes at the photonic crystal--air interface have the advantage of being accessible to the outside world, allowing one to take advantage of the defect-tolerant backscattering-free surface modes to engineer emission from photonic crystal surfaces into arbitrary free-space beam shapes and directions.

Production of two-colour radiation with polarisations of components rotating in opposite directions

A method is proposed for the production of two-colour radiation with monochromatic components, the polarisation vectors of which rotate in opposite directions, and the rotation speed is controlled by the sound frequency. The method is based on acousto-optic (AO) interaction upon double passage of two-colour radiation through an AO cell made of a gyrotropic crystal; the method efficiency is demonstrated by the example of radiation from an Ar laser generating at wavelengths of 0.488 and 0.514 μm and an AO cell made of TeO2, operating at a sound frequency of 60 MHz.

Stimulated multifrequency Raman scattering of light in a polycrystalline sodium bromate powder.

The observation of multifrequency stimulated Raman scattering of light in a thin powder layer of a gyrotropic crystal of sodium bromate when excited by intense ultrashort pulses of the second optical harmonic (λ=532nm) of an yttrium aluminum garnet laser is reported. Five Stokes and anti-Stokes satellites corresponding to the excitation of the intramolecular optical mode of NaBrO3 crystal were present in the recorded spectra. In addition, Raman satellites corresponding to the excitation of lattice modes, as well as their combinations with intramolecular modes, were found in the spectra of stimulated Raman scattering. The prospects of using stimulated Raman scattering spectroscopy for express analysis of gyrotropic media: gyrotropic polycrystals, crystalline amino acids, proteins, DNA, etc. have been established.

Floquet-Bloch waves in magnetophotonic crystals with transverse magnetic field

We solved the problem of Floquet-Bloch waves propagation in the one-dimensional gyrotropic magnetophotonic crystal with transverse magnetic field. New fundamental solutions of the Hill’s equation in crystal layers based on the Floquet theory for a third boundary value problem are obtained in the analytical form. The dispersion equation is found through fundamental solutions. The analysis of the dispersion properties of the structures depending on the material parameters was carried out and extraordinary surface waves inherent only in gyrotropic magnetophotonic crystals have been discovered.

Control of spin dynamics in artificial honeycomb spin-ice-based nanodisks

We report the experimental and theoretical characterization of the angular-dependent spin dynamics in arrays of ferromagnetic nanodisks arranged on a honeycomb lattice. The magnetic field and microwave frequency dependence, measured by broadband ferromagnetic resonance, reveal a rich spectrum of modes that is strongly affected by the microstate of the network. Based on symmetry arguments with respect to the external field, we show that certain parts of the ferromagnetic network contribute to the detected signal. A comparison of the experimental data with micromagnetic simulations reveals that different subsections of the lattice predominantly contribute to the high-frequency response of the array. This is confirmed by optical characterizations using microfocused Brillouin light scattering. Furthermore, we find indications that nucleation and annihilation of vortex-like magnetization configurations in the low-field range affect the dynamics, which is different from clusters of ferromagnetic nanoellipses. Our work opens up new perspectives for designing magnonic devices that combine geometric frustration in gyrotropic vortex crystals at low frequencies with magnonic crystals at high frequencies.

First-principle calculation of Chern number in gyrotropic photonic crystals.

As an important figure of merit for characterizing the quantized collective behaviors of the wavefunction, Chern number is the topological invariant of quantum Hall insulators. Chern number also identifies the topological properties of the photonic topological insulators (PTIs), thus it is of crucial importance in PTI design. In this paper, we develop a first principle computatioal method for the Chern number of 2D gyrotropic photonic crystals (PCs), starting from the Maxwell's equations. Firstly, we solve the Hermitian generalized eigenvalue equation reformulated from the Maxwell's equations by using the full-wave finite-difference frequency-domain (FDFD) method. Then the Chern number is obtained by calculating the integral of Berry curvature over the first Brillouin zone. Numerical examples of both transverse-electric (TE) and transverse-magnetic (TM) modes are demonstrated, where convergent Chern numbers can be obtained using rather coarse grids, thus validating the efficiency and accuracy of the proposed method.

Equivalence of electric, magnetic, and electromagnetic Chern numbers for topological photonic crystals

Haldane [S. Raghu and F. D. M. Haldane, Phys. Rev. A 78, 033834 (2008)] predicted an analog of the integer quantum Hall effect in gyrotropic photonic crystals, where the net number of electromagnetic edge modes moving left-to-right is given by a bulk Chern number. His prediction—topological effects are bona fide wave and not quantum phenomena—has been confirmed in a number of experiments [Z. Wang et al., Nature 461, 772–775 (2009)]. However, theoretical physicists have tacitly used three different definitions for the bulk Chern numbers that enter the bulk-edge correspondence—on the basis of electromagnetic Bloch functions, electric Bloch functions, and magnetic Bloch functions. We use vector bundle theoretic arguments to prove that in media such as those considered by Haldane, these three potentially different Chern numbers necessarily agree with one another, and consequently, any one of them can be used in Haldane’s photonic bulk-edge correspondence.

Multiple One-Way Edge States From Reciprocal Continuous Media

One-way edge states are emerging as a robust way to control light in $t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ $p\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}s$, in which a high gap Chern number is essential for generating multiple one-way edge states for multiplexing and demultiplexing circuits. Contrary to approaches using gyrotropic photonic crystals, this study shows how reciprocal continuous media with a gauge field and chirality can be used to generate a gap Chern number greater than 1, and to support a maximum of 4 one-way edge states. Such media can be further used to construct one-way signal combiners and splitters, in which branching and transmission efficiencies can be accurately controlled.

Peculiarities of the acousto-optical interactions of Bessel light beams in crystals

The noncollinear acousto-optical filtration of diffracted Bessel light beams in uniaxial paratellurite crystals has been investigated. With the use of the method of overlap integrals it is shown that independently on the order of Bessel light beams in the conditions of transverse phase-matching of diffracted waves in the range of optical spectrum of 0.4-1.1 nm in paratellurite crystals the bandwidth of transmission of ∼0.52 nm is reached due to detuning from Bragg’s synchronism only. It is shown that in uniaxial gyrotropic crystals polarization-independent diffraction of Bessel light beams is possible, i.e. Bragg diffraction efficiency is independent of the polarization state of the incident beam. It has been stated that the physical reason of such diffraction is simultaneous realization of two processes of anisotropic scattering under which the Bragg synchronism conditions are realized for the orthogonally polarized elliptical Bessel beams.

Orbital Edelstein effect from density-wave order

Coupling between charge and spin, and magnetoelectric effects more generally, have been an area of great interest for several years, with the sought-after ability to control magnetic degrees of freedom via charge currents serving as an impetus. The orbital Edelstein effect (OEE) is a kinetic magnetoelectric effect consisting of a bulk orbital magnetization induced by a charge current. It is the orbital analogue of the spin Edelstein effect in spin-orbit coupled materials, in which a charge current drives nonzero electron spin magnetization. The OEE has recently been investigated in the context of Weyl semimetals and Weyl metals. Motivated by these developments, we study a model of electrons without spin-orbit coupling which exhibits line nodes that get gapped out by via symmetry breaking due to an interaction-induced charge density wave order. This model is shown to exhibit a temperature dependent OEE, which appears due to symmetry reduction into a gyrotropic crystal class.