Spin-transfer torque and spin Hall effects combined with their reciprocal phenomena, spin pumping and inverse spin Hall effects (ISHEs), enable the reading and control of magnetic moments in ...spintronics. The direct observation of these effects remains elusive in antiferromagnetic-based devices. We report subterahertz spin pumping at the interface of the uniaxial insulating antiferromagnet manganese difluoride and platinum. The measured ISHE voltage arising from spin-charge conversion in the platinum layer depends on the chirality of the dynamical modes of the antiferromagnet, which is selectively excited and modulated by the handedness of the circularly polarized subterahertz irradiation. Our results open the door to the controlled generation of coherent, pure spin currents at terahertz frequencies.
A millimeter‐wave (MMW) dual‐band dual‐sense (DBDS) circular polarization (CP) antenna based on a chiral structure is presented. An arc parasitic patch is loaded around a circular patch to have ...chiral characteristics. This structure exhibits bi‐isotropy to the electromagnetic wave. The linear polarization (LP) wave passes through the chiral structure and excites the orthogonal left‐handed (LH) and right‐handed (RH) CP waves. The antenna is fabricated and measured. The LHCP radiation is achieved in the range between 23.75 and 24.25 GHz, and the RHCP radiation is between 27.75 and 28.25 GHz. The realized gains reach 6.9 dBic at 24 GHz and reach 7.1 dBic at 28 GHz. The proposed antenna has a profile of 1.044 mm (0.08 λ) and occupies an area of 0.54 λ × 0.54 λ, λ is the free‐space wavelength at the lower frequency and is convenient for array design.
Topological semimetals in crystals with a chiral structure (which possess a handedness due to a lack of mirror and inversion symmetries) are expected to display numerous exotic physical phenomena, ...including fermionic excitations with large topological charge1, long Fermi arc surface states2,3, unusual magnetotransport4 and lattice dynamics5, as well as a quantized response to circularly polarized light6. So far, all experimentally confirmed topological semimetals exist in crystals that contain mirror operations, meaning that these properties do not appear. Here, we show that AlPt is a structurally chiral topological semimetal that hosts new four-fold and six-fold fermions, which can be viewed as a higher spin generalization of Weyl fermions without equivalence in elementary particle physics. These multifold fermions are located at high symmetry points and have Chern numbers larger than those in Weyl semimetals, thus resulting in multiple Fermi arcs that span the full diagonal of the surface Brillouin zone. By imaging these long Fermi arcs, we experimentally determine the magnitude and sign of their Chern number, allowing us to relate their dispersion to the handedness of their host crystal.AlPt is shown to be a chiral topological material with four-fold and six-fold degeneracies in the band structure. Fermi arc edge states span the whole Brillouin zone and their dispersion enables identification of the handedness of the chiral material.
Supramolecular chiroptical switches Zhang, Li; Wang, Han-Xiao; Li, Shuai ...
Chemical Society reviews,
12/2020, Letnik:
49, Številka:
24
Journal Article
Recenzirano
Chiroptical switches, whose chiral optical signals such as optical rotatory dispersion (ORD), circular dichroism (CD) and circularly polarized luminescence (CPL) are reversibly interchangeable ...between two states, offer many promising applications in the fields of chiral sensing, optical displays, information storage, asymmetric catalysis and so on. Through various non-covalent interactions, supramolecular chiroptical switches have been constructed by combining the chiral and responsive functional components. This review summarizes the recent progress in the construction of supramolecular chiroptical switchable systems that reversibly respond to various stimuli, such as light, electricity, magnetic fields, mechanical force, solvents, pH, temperature, and chemical additives. The switching of supramolecular chirality in the forms of on/off, amplification/weakening and chirality inversion is shown. Additionally, the design of chiroptical switchable systems for chiral logic gates, data communication, chiral separation and asymmetric catalysis has been demonstrated. Future challenges in developing supramolecular chiroptical switches are also discussed.
Recent progress in chiroptical switches including on/off, amplification, and inversion of the chiral signals such as ECD and CPL in supramolecular assemblies is shown.
In this article, a dual circularly polarized high gain superstrate integrated X‐band antenna is designed and analyzed for CubeSat applications. The proposed antenna consists of a metallic patch, ...multilayer space qualified printed circuit boards, and a dielectric superstrate with a high relative permittivity on top of the patch to establish a suitable resonance condition for high‐gain operation. The driven patch is fed by a 3‐dB hybrid coupler for the generation of dual (left hand circular polarization and right hand circular polarization) circular polarization. The antenna exhibits an impedance bandwidth of >18.5% (7.75–9.4 GHz) with a peak gain of >16 dBiC. The achieved antenna performance makes it suitable for CubeSat missions at X‐band.
A dual circularly polarized (CP) magnetoelectric dipole antenna is presented in this article. The dual-CP antenna was devised to form a circular ring shape and fabricated using 3-D printing ...technology. To overcome the conflict between high (broadside) gain and wide (half-power) beamwidth, a new beamwidth broadening technique was proposed. Twelve meta-columns were placed evenly along the circumference close to the ring-shaped dipole. A design approach is elaborated, where the number and size of meta-columns were decided according to the design curves. Symmetrical beamwidth of 108° in orthogonal planes with a broadside gain of 6 dBic was achieved across a wide effective bandwidth from 3.2 to 5.4 GHz (51%), sufficiently covering the 5G new radio (NR) bands: <inline-formula> <tex-math notation="LaTeX">n77, n78, n79 </tex-math></inline-formula>. The antenna owns a compact size of <inline-formula> <tex-math notation="LaTeX">0.83 \times 0.83 \times 0.18\lambda ^{3} </tex-math></inline-formula> at 4.15 GHz. A planar subarray composed of four dual-CP elements was also investigated and compared with the existing arrays.
In this letter, a wide-angle beam-scanning antenna with circular polarization (CP) characteristic is proposed. The antenna consists of two layers. Microstrip spoof surface plasmon polariton (SPP) is ...introduced on the bottom layer as a slow-wave feeding line. A series of circular patches are placed on the top layer as radiating elements. Simulated and measured results indicate that beam-scanning angle of the proposed antenna is improved and CP beam-scanning ability is obtained by introducing perturbation on the radiating elements. In the operating band of 11-15 GHz, measured scanning angle of the fabricated antenna is from -32° to +34°. The antenna axial ratio (AR) is below 3 dB at the corresponding beam direction, and gain is above 12.8 dBi over the whole band. It has potential applications in radar and wireless communication systems for simple structure, low-cost fabrication, wide beam-steering, and CP properties.
It is well known that the spin angular momentum of light, and therefore that of photons, is directly related to their circular polarization. Naturally, for totally unpolarized light, polarization is ...undefined and the spin vanishes. However, for non-paraxial light, the recently discovered transverse spin component, orthogonal to the main propagation direction, is largely independent of the polarization state of the wave. Here, we demonstrate, both theoretically and experimentally, that this transverse spin survives even in non-paraxial fields (for example, focused or evanescent) generated from totally unpolarized paraxial light. This counterintuitive phenomenon is closely related to the fundamental difference between the meanings of ‘full depolarization’ for two-dimensional (2D) paraxial and 3D non-paraxial fields. Our results open an avenue for studies of spin-related phenomena and optical manipulation using unpolarized light.A theoretical and experimental study of the transverse spin appearing in non-paraxial light when the source is totally unpolarized is reported, in sharp contrast to the usual longitudinal spin, which is directly related to the 2D polarization and vanishes in unpolarized fields.
The dissymmetric interaction between circularly polarised (CP) light and chiral molecules is central to a range of areas, from spectroscopy and imaging to next-generation photonic devices. However, ...the selectivity in absorption or emission of left-handed
versus
right-handed CP light is low for many molecular systems. In this perspective, we assess the magnitude of the measured chiroptical response for a variety of chiral systems, ranging from small molecules to large supramolecular assemblies, and highlight the challenges towards enhancing chiroptical activity. We explain the origins of low CP dissymmetry and showcase recent examples in which molecular design, and the modification of light itself, enable larger responses. Our discussion spans spatial extension of the chiral chromophore, manipulation of transition dipole moments, exploitation of forbidden transitions and creation of macroscopic chiral structures; all of which can increase the dissymmetry. Whilst the specific strategy taken to enhance the dissymmetric interaction will depend on the application of interest, these approaches offer hope for the development and advancement of all research fields that involve interactions of chiral molecules and light.
This perspective explores the dissymmetric interaction between circularly polarised (CP) light and chiral molecules. Such interactions are central to many applications from next generation displays to asymmetric photochemical synthesis.
A novel gain enhancement method for a dual-polarized open-ended square waveguide antenna is proposed in this paper. Slots are etched on the sidewalls near the input of the open-ended square ...waveguide, which couple part of the energy to the periodic structures loaded on the sidewalls and excite the TM 0 modes. The surface wave is excited on the periodic structures. The periodic structures are equivalent to a dielectric rod with a graded dielectric constant. Part of the energy coupled to the periodic structures is radiated during the transmission, which combines with the energy radiated by the open waveguide, forming a plane wave to produce a high-gain end-fire beam in the far field. The antenna is printed using Stereo Lithography Appearance (SLA) 3D printing technology, and then a layer of copper is plated on the outer surface to make the antenna equivalent to an all-metal structure. Compared with the dielectric-loaded open-ended waveguide antennas, 3D-printed all-metal periodic structures reduce dielectric loss and processing costs. The antenna structure is a square waveguide, so an orthogonal-mode transducer (OMT) and circular polarizer can be used to achieve dual linear polarization (LP) and dual circular polarization (CP). The simulated results show that the proposed antenna achieves a gain enhancement of about up to 8dB (Compared with an unloaded open waveguide antenna). The measured results show that a peak gain of 17.8 dBi is realized for LP states. The antenna is very suitable for millimeter-wave high-gain application scenarios, such as point-to-point communication applications.
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