Polar Symmetry Research Articles

Stabilization of phase-pure rhombohedral HfZrO4 in pulsed laser deposited thin films

Controlling the crystalline structure of Hafnium Zirconate and its epitaxial relationship to a semiconducting electrode has a high technological interest, as ferroelectric materials are key ingredients for emerging electronic devices. Using Pulsed Laser Deposition, a phase pure, ultra-thin film of HfZrO4 is grown epitaxially on a GaN (0001) / Si (111) template. Since standard microscopy techniques do not allow to determine with certitude the crystalline structure of the film due to the weak scattering of oxygen, differentiated differential phase contrast (DPC) Scanning Transmission Electron Microscopy is used to allow the direct imaging of oxygen columns in the film. Combined with X-Rays diffraction analysis, the polar nature and rhombohedral R3 symmetry of the film are demonstrated.

Magnetoelectric effects in gyrotropic superconductors

The magnetoelectric effect (or Edelstein effect) in noncentrosymmetric superconductors states that a supercurrent can induce spin magnetization. This is an intriguing phenomenon which has potential applications in superconducting spintronic devices. However, the original Edelstein effect only applies to superconductors with polar point group symmetry. In recent years, many new noncentrosymmetric superconductors have been discovered, such as superconductors with chiral lattice symmetry and superconducting transition metal dichalcogenides with various lattice structures. In this Rapid Communication, we provide a general framework to describe the supercurrent-induced magnetization in these recently discovered superconductors with gyrotropic point groups.

Polar coupling enabled nonlinear optical filtering at MoS2/ferroelectric heterointerfaces

Complex oxide heterointerfaces and van der Waals heterostructures present two versatile but intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS2 and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhanced or almost entirely quenched by an underlying ferroelectric domain wall depending on its chirality, and can be further tailored by the polar domains. Unlike the extensively studied coupling mechanisms driven by charge, spin, and lattice, the interfacial tailoring effect is solely mediated by the polar symmetry, as well explained via our density functional theory calculations, pointing to a new material strategy for the functional design of nanoscale reconfigurable optical applications.

Analyses of structure, electronic and multiferroic properties of Bi1-xNdxFeO3 (x = 0, 0.05, 0.10, 0.15, 0.20, 0.25) system

Magnetoelectric multiferroics are of considerable interest due to the fascinating science and potential applications. In this study, multiferroic Bi1-xNdxFeO3 (0 ≤ x ≤ 0.25) samples have been prepared by a two-stage solid-state reaction method and correlation between various properties has been studied. It can be seen that Nd3+ substitution destabilized the polar R3c symmetry due to chemical strain effects arising from the size mismatch between Bi3+ and Nd3+ cations which triggered partial structural transformation to triclinic structure (P1symmetry). Raman scattering experiments elucidated slight changes in covalency of Bi–O bond and softening of modes corresponding to oxygen motion suggests a significant destabilization of FeO6 octahedra. The increase in magnetization has been attributed to the suppression of the spiral spin structure and variation in Fe–O–Fe bond angle due to the strain induced in the unit cell by Nd3+ substitution. The step-like feature in magnetization at the low field has been attributed to charge melting in connection with manganites. An anomalous decrease in coercivity with decrease in temperature has been observed for Bi0.75Nd0.25FeO3 sample which can be explained on the basis that the decrease in effective magnetic anisotropy and is an indicator of presence of magnetoelectric coupling. The bandgap increases with increase in Nd3+ content which is attributed to the decrease in interatomic lattice parameters which resulted in increased binding forces of valance electrons.

Centrosymmetry Breaking and Ferroelectricity Driven by Short-Range Magnetic Order in the Quadruple Perovskite (YMn3)Mn4O12.

By means of single-crystal X-ray diffraction, we give direct crystallographic evidence of a centrosymmetry breaking below TS = 200 K, concomitant with the onset of a commensurate structural modulation in the quadruple perovskite YMn3Mn4O12. This result, which explains the anomalously large thermal coefficient of the Y3+ ion in previously reported structural models, is attributed to the small size of the Y3+ ion, which causes its underbonding within the dodecahedral coordination polyhedron. The present data are consistent with a commensurate superstructure described by an I-centered pseudo-orthorhombic cell with polar Ia symmetry and a ≈ aF√2 = 10.4352(7) Å, b ≈ 2bF = 14.6049(9) Å, c ≈ cF√2 = 10.6961(7) Å, and β = 90.110(3)°, where aF ≈ cF ≈ 7.45 Å, bF ≈ 7.34 Å, and β ≈ 91° are the unit cell parameters of the I2/m structure observed at room temperature. Consistent with the above polar structure, at lower temperature, T* = 70 K, we observe in polycrystalline samples an anomaly of the direct current (DC) and alternating current (AC) magnetization, concomitant with the appearance of a net electric polarization, as indicated by pyrocurrent and dielectric constant measurements. These results, complemented by electrical transport measurements, suggest a magnetic ferroelectricity driven by short-range magnetic order in YMn3Mn4O12.

A mathematical model for root canal preparation using Endodontic file

AimTo develop the mathematical model for root canal preparation using Endodontic file. MethodThe process of obturation consist of the filling of the root canal cavity using heated and softened gutta-percha to get the fluid tight seal in between the canal wall and filled gutta-percha. Any obturation process to perform before it requires the preparation of the root canal which involves the removing dead tissue, substrates and debris from the decayed root canal. The various geometric parameters viz. Taper, relative angle for orientation of cross-section between two planes, pitch and polar symmetry constant of the Endodontic file etc. Geometric parameters are derived. The various performance parameters like Endodontic file life assessment, cutting force components (tangential and normal), substrate removal rate, torque exerted by Endodontic file etc are also derived successfully. The Endodontic file life is estimated based on two approaches viz. speed and volumetric wear approach. ConclusionThe mathematical model described is helpful for the Endodontic experts, researchers, design engineers etc. However the applicability of the described mathematical model limited to assumption of study. The gap between root canal to be prepared and Endodontic file is zero while preparation. The Endodontic file weight, speed of rotation and substrate removal rate is assumed to be constant. The mathematical model for Endodontic file discussed above proved to be efficient tool for studying the root canal preparation. The various geometric parameters and the various performance parameters are derived.

Morphotropic Relaxor Boundary in a Relaxor System Showing Enhancement of Electrostrain and Dielectric Permittivity.

In ferroelectric and relaxor-ferroelectric materials, piezoelectric and dielectric properties are significantly enhanced at the morphotropic phase boundary (MPB), a boundary between different ferroelectric phases with different macroscopic symmetries. By contrast, in relaxor systems, such an MPB does not exist because relaxors of different compositions possess the same macroscopic symmetry. Here, we report the existence of a morphotropic relaxor boundary (MRB) in the single phase relaxor region of a K_{0.5}Na_{0.5}NbO_{3}-xBaTiO_{3} system, which is a composition-induced boundary between two relaxors with different local polar symmetries (tetragonal versus rhombohedral) but with the same macroscopic cubic symmetry. At the MRB the electrostrain increases by ∼3 times and the permittivity increases by ∼1.5 times over a wide temperature range of more than 100K, as compared with off-MRB compositions. Our Letter demonstrates that the MRB may become an effective mechanism to enhance the dielectric and electrostrictive properties of relaxors.

2.5-D Miniaturized Multifunctional Active Frequency-Selective Surface

In this paper, a 2.5-D approach has been used to design 2.5-D miniaturized multifunctional active frequency-selective surfaces (2.5-D MMAFSSs). The unitary element, based on the via-connected metal strips and metallic parallel plates, can be miniaturized to 0.063λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength. To achieve the relative polarization symmetry, four similar subcells based on the unitary element are combined together to constitute a 2.5-D MMAFSS unit cell. The novelty of the proposed design lies in four independent operating states that can be realized by actively changing the on-off states of p-i-n diodes. In addition, the miniaturized configuration is beneficial for the easy realization of multiple electromagnetic states with great angle stability and polarization insensitivity. For a better understanding of the physical principle, the analyses of both surface current and electric field distributions are conducted at resonance frequencies. Also, the equivalent circuit models are established to further clarify the working mechanism of the structure. Finally, a prototype of the 2.5-D MMAFSS operating at 1.9 GHz is fabricated and measured to validate the proposed concept, and the experimental results are in satisfactory agreement with the simulated ones.

Magnetic inversion symmetry breaking and spin reorientation in Tb2MnNiO6 : A polar strong ferromagnet

We report a description and comprehensive study on four successive magnetic transitions in ferromagnetic $\mathrm{T}{\mathrm{b}}_{2}\mathrm{MnNi}{\mathrm{O}}_{6}$ double perovskite. In the ground state ($P{2}_{1}^{\ensuremath{'}}$), the moments of magnetic $A$ and $B$ sites order according to different nonpolar magnetic modes, but the coupling between them generates an overall polar symmetry which makes this oxide potentially multiferroic due to magnetic trilinear coupling, and therefore ferromagnetic and ferroelectric in its ground state. Its macroscopic magnetization is large ($5\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}$) and not related to a weak ferromagnetic component induced by Dzyaloshinskii-Moriya interaction. However, a sharp and severe spin reorientation of the ferromagnetic transition-metal moments has been observed which opens the door to the magnetic switching of the ferroelectric state in this perovskite, and conversely to the control of the magnetization direction by electrical fields applied parallel to $b$. We also anticipate that in this material the direction of the magnetization (towards $c/a$) could be used as the key to switch the polar/nonpolar (ferroelectric/antiferroelectric) transformation.

Optical control of the layer degree of freedom through Wannier–Stark states in polar 3R MoS2

Electrons in two-dimensional layered crystals gain a discrete positional degree of freedom over layers. We propose the two-dimensional transition metal dichalcogenide homostructure with polar symmetry as a prototypical platform where the degrees of freedom for the layers and valleys can be independently controlled through an optical method. In 3R MoS2, a model system, the presence of the spontaneous polarization and built-in electric field along the stacking axis is theoretically proven by the density functional theory. The K valley states under the electric field exhibit Wannier–Stark type localization with atomic-scale confinement driven by double group symmetry. The simple interlayer-dynamics-selection rule of the valley carriers in 3R homostructure enables a binary operation, upward or downward motion, using visible and infrared light sources. Together with the valley-index, a 2 2 states/cell device using a dual-frequency polarized light source is suggested.

Symmetry-determined antiferroelectricity in PbZrO3 , NaNbO3 , and PbHfO3

Like ferroelectric or ferroelastic phase transitions, antiferroelectric transitions can be predicted by symmetry. This property is illustrated by a theoretical analysis of the complex phase transitions, occurring in the perovskite compounds $\mathrm{PbZr}{\mathrm{O}}_{3}$, $\mathrm{NaNb}{\mathrm{O}}_{3}$, and $\mathrm{PbHf}{\mathrm{O}}_{3}$, which involve the coupling of several order parameters. The symmetry-breaking order parameters associated with the transitions in the three compounds are determined. The antiferroelectric transitions are shown to verify specific symmetry criteria, which consist of the emergence at the local scale of polar site symmetries coinciding with symmorphic subgroups of the antiferroelectric space group. The theoretical temperature--electric-field phase diagram of $\mathrm{PbZr}{\mathrm{O}}_{3}$ involving ferrielectric and ferroelectric phases is worked out.

Interplay of Polarization and Time-Reversal Symmetry Breaking in Synchronously Pumped Ring Resonators.

Optically induced breaking of symmetries plays an important role in nonlinear photonics, with applications ranging from optical switching in integrated photonic circuits to soliton generation in ring lasers. In this work we study for the first time the interplay of two types of spontaneous symmetry breaking that can occur simultaneously in optical ring resonators. Specifically we investigate a ring resonator that is synchronously pumped with short pulses of light. In this system we numerically study the interplay and transition between regimes of temporal symmetry breaking (in which pulses in the resonator either run ahead or behind the seed pulses) and polarization symmetry breaking (in which the resonator spontaneously generates elliptically polarized light out of linearly polarized seed pulses). We find ranges of pump parameters for which each symmetry breaking can be independently observed, but also a regime in which a dynamical interplay takes place. Besides the fundamentally interesting physics of the interplay of different types of symmetry breaking, our work contributes to a better understanding of the nonlinear dynamics of optical ring cavities which are of interest for future applications including all-optical logic gates, synchronously pumped optical frequency comb generation, and resonator-based sensor technologies.

Ultrafast Zero-Bias Surface Photocurrent in Germanium Selenide: Promise for Terahertz Devices and Photovoltaics.

Theory predicts that a large spontaneous electric polarization and concomitant inversion symmetry breaking in GeSe monolayers result in a strong shift current in response to their excitation in the visible range. Shift current is a coherent displacement of electron density on the order of a lattice constant upon above-bandgap photoexcitation. A second-order nonlinear effect, it is forbidden by the inversion symmetry in the bulk GeSe crystals. Here, we use terahertz (THz) emission spectroscopy to demonstrate that ultrafast photoexcitation with wavelengths straddling both edges of the visible spectrum, 400 and 800 nm, launches a shift current in the surface layer of a bulk GeSe crystal, where the inversion symmetry is broken. The direction of the surface shift current determined from the observed polarity of the emitted THz pulses depends only on the orientation of the sample and not on the linear polarization direction of the excitation. Strong absorption by the low-frequency infrared-active phonons in the bulk of GeSe limits the bandwidth and the amplitude of the emitted THz pulses. We predict that reducing GeSe thickness to a monolayer or a few layers will result in a highly efficient broadband THz emission. Experimental demonstration of THz emission by the surface shift current in bulk GeSe crystals puts this 2D material forward as a candidate for next-generation shift current photovoltaics, nonlinear photonic devices, and THz sources.

Propagation characteristics of periodic structures possessing twist and polar glide symmetries

In this article, we provide an overview of the current state of the research in the area of twist symmetry. This symmetry is obtained by introducing multiple periods into the unit cell of a periodic structure through a rotation of consecutive periodic deformations around a symmetry axis. Attractive properties such as significantly reduced frequency dispersion and increased optical density, compared to purely periodic structures, are observed. The direct link between the symmetry order and these properties is illustrated through numerical simulations. Moreover, polar glide symmetry is introduced, and is shown to provide even further control of the dispersion properties of periodic structures, especially when combined with twist symmetry. Twist symmetries can, with benefit, be employed in the development of devices for future communication networks and space applications, where fully metallic structures with accurate control of the dispersion properties are desired.

Mixed-Valence Iron Dumortierite Fe13.52.22+(As5+O4- x)8(OH)6 and Its Intricate Topotactic Exsolution at Mild Temperatures.

The mixed-valent iron arsenate hydroxide Fe13.52.22+(AsO4- x)8(OH)6, x = 0.25, was prepared using the reaction of iron metal with arsenate in aqueous solution and autogenous pressure. Its crystal structure reveals a dumortierite-like framework with mixed-valent Fe2+/Fe3+ in double chains creating channel walls. Remarkably, hexagonal channels consist of chains of face-sharing Fe2+O6 octahedra, 3/4th occupied, whereas AsO4 tetrahedra occupy triangular ones with a single " up" orientation according to the polar P63 mc symmetry. We have analyzed the transformation of this phase upon heating, in which several chemical processes interact, including dehydroxylation, arsenate to arsenite reduction, and oxidative exsolution of a significant part of iron (ca. 15%) found at the surface as hematite and amorphous Fe-rich surficial layer. It leaves a strongly disordered composite structure between several Fe3+-based subunits, in which ∼80% of them is ordered in a complex supercell. Because of the high degree of disorder, the crystal chemistry of the individual subunits and their plausible imbrication were considered to unravel the most plausible ideal 3D model.

A Stemness Screen Reveals C3ORF54/INKA1 As a Gate-Keeper of Human Stem Cell Latency

The controversy generated from recent murine studies as to whether hematopoietic stem cells (HSC) contribute to steady-state hematopoiesis emphasizes how limited our knowledge is of the mechanisms governing HSC self-renewal, activation and latency; a problem most acute in the study of human HSC and leukemia stem cells (LSC). Many hallmark stem cell properties are shared by HSC and LSC and therefore a better understanding of stemness regulation is crucial to improved HSC therapies and leukemia treatments targeting LSC.Our previous work on LSC subsets from >80 AML patient samples revealed that HSC and LSC share a transcriptional network that represent the core elements of stemness (Eppert, Nature Med 2011; Ng, Nature 2016). Hence, to identify the key regulators of LSC/HSC self-renewal and persistence we selected 64 candidate genes based on expression in functionally validated LSC vs. non-LSC fractions and assessed their potential to enhance self-renewal in a competitive in vivo screen.Here, we transduced cord blood CD34+CD38- cells with 64 barcoded lentiviral vectors to assemble 16 pools, each consisting of 8 individual gene-transduced populations, for transplantation into NSG mice. Strikingly, individual overexpression (OE) of 5 high scoring candidates revealed delayed repopulation kinetics of human HSC/progenitor cells (HSPC): gene-marking of human CD45+ and lin-CD34+ cells was reduced relative to input and control at 4w post transplantation, whereas by 20w engraftment of marked cells reached or exceeded input levels. For one of these candidates, C3ORF54/INKA1, we found that OE did not alter lineage composition neither in in vitro nor in vivo assays but increased the proportion of primitive CD34+ cells at 20w in vivo; moreover, secondary transplantation revealed a 4.5-fold increase in HSC frequency. Of note, serial transplantation from earlier time points (2w, 4w) revealed superior engraftment and hence greater self-renewal capacity upon INKA1-OE. Since we observed a 4-fold increase of phenotypic multipotent progenitors (MPP) relative to HSC within the CD34+ compartment (20w) we assessed whether INKA1-OE acts selectively on either cell population. The observation of latency in engraftment was recapitulated with sorted INKA1-OE HSC but not MPP.Likewise, liquid culture of HSPC and CFU-C assays on sorted HSC showed an initial delay in activation and colony formation upon INKA1-OE that was completely restored by extended culture and secondary CFU-C, respectively. INKA1-OE MPP showed a slight increase in total colony count in primary CFU-C and increased CDK6 levels in contrast to reduced CDK6 levels in INKA1-OE HSC emphasizing opposing effects of INKA1 on cell cycle entry and progression in either population. Taken together, this suggests that INKA1-OE preserves self-renewal capacity by retaining HSC preferentially in a latent state, however, upon transition to MPP leads to enhanced activation.Whilst INKA1 has been described as an inhibitor of p21(Cdc42/Rac)-activated kinase 4 (PAK4), no role for PAK4 is described in hematopoiesis. Nonetheless, its regulator Cdc42 is implicated in aging of murine HSPC by affecting H4K16 acetylation (H4K16ac) levels and polarity and has recently been described to regulate AML cell polarity and division symmetry. In our experiments immunostaining of HSPC subsets cultured in vitro and from xenografts indicates that INKA1-OE differentially affects epigenetics of these subsets linking H4K16ac to the regulation of stem cell latency.In AML, transcriptional upregulation of INKA1 in LSC vs. non-LSC fractions and at relapse in paired diagnosis-relapse analysis (Shlush, Nature 2017) implicates INKA1 as a regulator of LSC self-renewal and persistence. Indeed, INKA1-OE in cells derived from a primary human AML sample (8227) with a phenotypic and functional hierarchy (Lechman, Cancer Cell 2016) revealed a strong latency phenotype: In vitro and in vivo we observed label retention along with a steady increase in percentage of CD34+ cells, transient differentiation block, reduced growth rate, G0 accumulation and global reduction of H4K16ac.In summary, our data implicates INKA1 as a gate-keeper of stem cell latency in normal human hematopoiesis and leukemia. Studying the detailed pathways involved will shed light upon the mechanisms involved in HSC activation and latency induction and will help to harness these for novel therapeutic approaches. DisclosuresTakayanagi:Kyowa Hakko Kirin Co., Ltd.: Employment.

Magnetoelectric multipoles in metals

In this paper, we demonstrate computationally the existence of magnetoelectric multipoles, arising from the second-order term in the multipole expansion of a magnetization density in a magnetic field, in non-centrosymmetric magnetic metals. While magnetoelectric multipoles have long been discussed in the context of the magnetoelectric effect in non-centrosymmetric magnetic insulators, they have not previously been identified in metallic systems, in which the mobile carriers screen any electrical polarization. Using first-principles density functional calculations, we explore three specific systems: first, a conventional centrosymmetric magnetic metal, Fe, in which we break inversion symmetry by introducing a surface, which both generates magnetoelectric monopoles and allows a perpendicular magnetoelectric response. Next, the hypothetical cation-ordered perovskite, SrCaRu2O6, in which we study the interplay between the magnitude of the polar symmetry breaking and that of the magnetic dipoles and multipoles, finding that both scale proportionally to the structural distortion. Finally, we identify a hidden antiferromultipolar order in the non-centrosymmetric, antiferromagnetic metal Ca3Ru2O7, and show that, while its competing magnetic phases have similar magnetic dipolar structures, their magnetoelectric multipolar structures are distinctly different, reflecting the strong differences in transport properties.This article is part of the theme issue 'Celebrating 125 years of Oliver Heaviside's 'Electromagnetic Theory''.

Optic axis mapping with catheter-based polarization-sensitive optical coherence tomography.

Birefringence offers an intrinsic contrast mechanism related to the microstructure and arrangement of fibrillary tissue components. Here we present a reconstruction strategy to recover not only the scalar amount of birefringence but also its optic axis orientation as a function of depth in tissue from measurements with catheter-based polarization sensitive optical coherence tomography. A polarization symmetry constraint, intrinsic to imaging in the backscatter direction, facilitates the required compensation for wavelength-dependent transmission through system elements, the rotating catheter, and overlying tissue layers. Applied to intravascular imaging of coronary atherosclerosis in human patients, the optic axis affords refined interpretation of plaque architecture.

Combined half-integer Bessel-like beams: A set of solutions of the wave equation

We report a family of solutions of the homogeneous free-space scalar wave equation. These solutions are determined by linear combinations of the half-integer order Bessel functions. We call these beams ``combined half-integer Bessel-like beams.'' It is shown that, by selecting suitable combinations of the half-integer order Bessel functions, a wide set of beams can be produced in which they may carry the orbital angular momentum (OAM) or not. We show that this family of beams satisfies a ``radial structured'' boundary condition at $z=0$ plane, therefore they can be produced by the diffraction of a plane wave from suitable ``radial structures.'' Some specific examples of the half-integer Bessel-like beams are introduced. Especially, a set of spatially asymmetric beams, having half-integer OAM, is introduced that can be used to make the concentration of the absorbing and dielectric micro- or nanoparticles in a microsolution inhomogeneous. Also, by manipulating the Fourier series of the radial structures, three subfamily of beams can be produced including the radial carpet, petallike, and ringlike vortex beams. The intensity profile of the petallike beams forms two dimensional optical latices with polar symmetry at the transverse plane. The ringlike vortex beams carry OAM. Here, by solving the wave equation we present the full image of the radial carpet beams. All the presented beams have nondiffracting, accelerating, and self-healing features. The combined half-integer Bessel-like beams can be considered in other areas of wave phenomena, ranging from sound and elastic waves to many other kinds of classical waves. Therefore, this work has profound implications in many linear wave systems in nature.

The POLICRYPS liquid-crystalline structure for optical applications

Abstract We present a review of polymer-liquid crystal-based devices for optical applications. Starting from a particular fabrication technique, which enables to obtain the POLICRYPS (POlymer LIquid CRYstal Polymer Slices) structure, we illustrate different realizations, along with their working principle and main features and performances. The name POLICRYPS indicates a structure made of parallel slices of pure polymeric material alternated to films of well-aligned nematic liquid crystal (NLC), with a spatial periodicity that can be settled in the range 0.2÷15 μm. Suitably designed samples can be utilized as optical devices with a high efficiency, which can be switched on and off both by applying an electric field of a few V/μm or by irradiating samples with a suitable light beam. In different geometries, POLICRYPS can be specialized to operate as switchable diffraction grating, switchable optical phase modulator, switchable beam splitter, or tunable Bragg filter. The POLICRYPS framework can be also used as a soft matter template for aligning different types of LCs or to create an array of tunable microlasers. Finally, we present a POLICRYPS structure with a polar symmetry of the director alignment, which enables local shaping of light polarization, allowing to convert circularly polarized beams into cylindrical vector beams.