Engineering terahertz surface magnon-polaritons in hyperbolic antiferromagnets

Magnetic crystals were recently studied as a route to hyperbolic dispersion and the effects associated with it. These studies, however, concentrated on bulk waves and frequencies where transmission is possible and where negative refraction occurs. Here, in contrast, we concentrate on geometries which sample regions of the dispersion relations where bulk propagation is not possible. This is done by controlling the orientation of the uniaxial anisotropy axis with respect to the surface of the crystal. Furthermore, we find that new magnetic surface polaritons exist in these regions, and we investigate the nature of these waves. In addition, significant tunability can be introduced by applying an external field perpendicular to the easy axes of a uniaxial antiferromagnet, creating a canted structure and generally shifting the frequencies to higher values. This externally applied field dramatically changes the nature of both surface and bulk polaritons, making them highly nonreciprocal

Electric and magnetic fields effects on the excitonic properties of elliptic core-multishell quantum wires

The effect of eccentricity distortions of core-multishell quantum wires on their electron, hole and exciton states is theoretically investigated. Within the effective mass approximation, the Schrodinger equation is numerically solved for electrons and holes in systems with single and double radial heterostructures, and the exciton binding energy is calculated by means of a variational approach. We show that the energy spectrum of a core-multishell heterostructure with eccentricity distortions, as well as its magnetic field dependence, are very sensitive to the direction of an externally applied electric field, an effect that can be used to identify the eccentricity of the system. For a double heterostructure, the eccentricities of the inner and outer shells play an important role on the excitonic binding energy, specially in the presence of external magnetic fields, and lead to drastic modifications in the oscillator strength.Comment: 17 pages, 10 figure

Screening for canine coronavirus, canine influenza virus, and severe acute respiratory syndrome coronavirus 2 in dogs during the coronavirus disease-2019 pandemic

Background and Aim: Although most cases of coronavirus disease-2019 (COVID-19) are in humans, there is scientific evidence to suggest that the virus can also infect dogs and cats. This study investigated the circulation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), canine coronavirus (CCV), and canine influenza virus (CIV) in domiciled and/or stray dogs from different locations in the State of Minas Gerais, Brazil, during the COVID-19 pandemic. Materials and Methods: In total, 86 dogs living in homes, on the streets, or in shelters in the cities of Taiobeiras, Salinas, Araçuaí, and Almenara were randomly selected for this study. The COVID Ag Detect® Self-Test was used to detect SARS-CoV-2. The ACCUVET CCV AG TEST – CANINE CORONAVIROSIS® was used to detect CCV, whereas canine influenza was detected using the ACCUVET CIV AG TEST – INFLUENZA CANINA®. All collected data were mapped using QGIS 3.28.1 for spatial data analysis and the identification of disease distribution patterns. Descriptive analysis of the collected data, prevalence calculations, odds ratios (ORs), and 95% confidence intervals, when possible, was performed. Results: Of the 86 animals tested, only one dog tested positive for SARS-CoV-2 using the rapid test for viral antigen detection. No animals tested positive for CIV. Canine coronavirus was detected in almost half of the animals tested in Almenara. Severe acute respiratory syndrome-CoV-2 had a low prevalence (1.16%), versus 15.62% for CCV. Although the results were not significant, the age and breed of animals appeared to be associated with the occurrence of CCV. The results indicated that younger animals were 2.375-fold more likely to be infected. Likewise, purebred animals were more likely to contract the disease (OR = 1.944). Conclusion: The results indicate the need to maintain preventive measures against CCV, canine influenza, and SARS-CoV-2 in dogs. More studies are needed to better elucidate the panorama of these diseases in dogs, mainly in underdeveloped and developing countries

The 2021 magnetic hyperbolic polaritons roadmap

This roadmap provides viewpoints on some of the key developments in the field of magnetic hyperbolic polaritons as well as discusses some of the crucial challenges in this emerging field. In particular, it discusses routes for optimising electromagnetic behavior in natural magnetic materials, how artificial structures can be used to design novel phenomena, and how two-dimensional materials can provide a completely new avenue to explore hyperbolic behavior

Extreme enhancement of nonreciprocal wave propagation in magneto-optical metamaterials

We investigate the magnetic field-induced spectral properties of metamaterials incorporating indium antimonide (InSb), using electromagnetic probes in the low terahertz (THz) frequency regime. An effective medium theory has been developed to explore the behavior of InSb interspersed with a simple dielectric in a grating-like structure with various thicknesses and grating filling factors. The metamaterial grating structure impacts the light-matter interactions and substantially modifies reflectivity. Our numerical results demonstrate how nonreciprocal reflection can be enhanced and controlled in this spectral region through the composition of the magnetic grating. The current need for higher frequency communication technology drives the relevancy of this study for application to directional-dependent THz devices

Electromagnetic waves in canted magnets

The optical properties of canted antiferromagnets are discussed from the perspective of magnetic polaritons and field tunable electromagnetic (EM) properties. Canted antiferromagnets have a weak magnetization. Their EM properties can be affected by externally applied magnetic fields as well as electric fields, if the material is multiferroic. A theoretical approach that is useful for describing the THz frequency EM response and properties of a large variety of canted spin systems is outlined here. The properties of two example systems are discussed: an antiferromagnet in which spin canting is induced through an externally applied magnetic field; and an antiferromagnetic multiferroic wherein the magnetic sublattices are canted through an internal coupling to a spontaneous dielectric polarization

Controlling asymmetric transmission in layered natural hyperbolic crystals

We explore the electromagnetic properties of a structure composed of two optically active materials—each layer contains a hyperbolic crystal with its anisotropy axis rotated with respect to the crystal surface. Through this, we can control the transmission spectra where at one frequency, light with a positive incidence angle is transmitted while it is absorbed for a negative incidence angle and the reverse occurs at a second frequency. Using a Gaussian beam analysis, we determine in which material layer the absorption occurs. In a radiating line current source study, we obtain tunable output collimated beams. From these discoveries, our structure can be applied as an efficient frequency or angle selector, demultiplexer, or filter

Vertically stacked soliton-like domain walls in nematic liquid crystals

In the standard liquid crystal (LC) geometry, one generally finds a quasi-parabolic director profile in the vertical direction, where the directors are aligned with an applied field in the center of the cell. In contrast, using a numerical energy minimization approach, we find that there are multiple metastable solutions where the director profile is oscillatory. At low voltages, we find small oscillations, which evolve into standard soliton-like domain walls as the applied voltage is increased. We predict the thickness of the domain wall with a simple analytic model that gives a good comparison to our numerical calculations, in the standard domain wall regime. For dual-frequency nematic LCs, the occurrence of this regime can be tuned by a change of the biasing frequency. Moreover, we investigate how domain walls can affect the optical properties of LC-based devices. For instance, we find that the transmittance curve shifts to higher voltages as domain walls are introduced. This shift can be used to create an efficient tunable filter

All-Angle Negative Refraction from the Phonon Response in Anisotropic Crystals

We consider how all-angle negative refraction may be induced in anisotropic crystals by making use of the phonon response. We investigate, both theoretically and experimentally, the example of crystal quartz at far infrared wavelengths