Giant photonic spin Hall effect induced by hyperbolic shear polaritons.

Recently, broken symmetry within crystals has been attracting tremendous research interest since it can be utilized to effectively manipulate the propagation of photons. In particular, low-symmetry Bravais crystals can support hyperbolic shear polaritons (HShPs), holding great promise for technological upgrading in the emerging research area of spinoptics. Herein, an Otto-type multilayer structure consisting of a KRS5 prism, a sensing medium, and monoclinic ß-Ga2O3 crystals is designed to ameliorate the photonic spin Hall effect (PSHE). The surface of ß-Ga2O3 is the monoclinic (010) plane (x-y plane). We show that giant spin Hall shifts with three (or two) orders of magnitude of the incident wavelength can be obtained in the in-plane (or transverse) directions. The azimuthal dispersions of photonic spin Hall shifts present non-mirror-symmetric patterns upon tuning the rotation angle of ß-Ga2O3 around the z-axis in the plane. All of these exotic optical properties are closely correlated with the broken crystal lattice symmetry and the incurred excitation of HShPs in monoclinic ß-Ga2O3 crystals. By virtue of the remarkably enhanced PSHE, our proposed Otto-type multilayer structure shows a superior biosensing performance in which the maximum sensitivity is two orders of magnitude larger than that of previously reported PSHE biosensors based on two-dimensional materials. In addition, the optimized physical and structural parameters including the incident angle, excitation wavelength, azimuth angle and doping concentration of ß-Ga2O3, thickness and refractive index of sensing medium are also investigated and presented. This work unequivocally confirms the strong influence of crystal symmetry on the PSHE, providing important insights into understanding the rich modulation of spin-orbit interactions of light via shear polaritons and therefore facilitating potential applications in photoelectronic devices.

Spin Hall effect of transmitted light through α-Li3N-type topological semimetals.

The spin Hall effect of light occurring in topological semimetals provides unprecedented opportunities to exploit novel photonic properties and applications. In particular, pristine α-Li3N-type crystal has recently been predicted to be a type-I nodal-line semimetal based on density functional theory. Herein, the spin Hall effect of transmitted light through thin films of α-Li3N-type topological semimetals is investigated. We show that the prominent intense peak and dip emerging in the spectra of spin Hall shifts occur at the high-energy side of interband absorption of α-Li3N-type semimetals and show redshifts with increasing the incident angle or permittivity of the exit medium. In addition, type-I nodal-line semimetal under a compressive lattice strain is transformed into a type-II one such that the main intense peak and dip show blueshifts. Inversely, the tensile strain induces the formation of a triply degenerate nodal point in α-Li3N-type semimetals, causing the main intense peak and dip to show redshifts. Moreover, the influences of alloying and hole-doping in α-Li3N-type semimetals on the spin Hall effect of light are also discussed. Our findings may provide clear strategies to accurately engineer and detect the structural or phase change in topological materials.

Temperature-dependent circular conversion dichroism from chiral metasurfaces patterned in Dirac semimetal Cd3As2.

Chiral metasurfaces patterned with L-shaped holes in a thin film of Dirac semimetal Cd3As2 are designed. The impact of temperature T on circular conversion dichroism, mainly characterized by circular polarization differential transmittance (CPDT), is studied by rigorous coupled-wave analysis. The results show that decreasing T will give rise to the appearance of much more narrow CPDT peaks and dips, and the maximum differential transmittance between two opposite circularly polarized light can reach above 0.60 by optimizing the structural parameters at 80 K. As the T increases, the differential transmittance gradually decreases, and the CPDT peak and dip values exhibit variation tendencies of 'Z' and 'S' types, respectively. Two simple formulae of CPDT extreme values with respect to T are derived, predicting that the decreasing tendency will reach saturation when T ≥ 500 K. Differing from the wavelength-independent variation trend of differential transmittance, CPDT extremum positions mainly show a blueshift (redshift) tendency at the wavelength λ > 10 µm (λ < 5 µm) as the T increases. Moreover, evolutions of CPDT with various factors including the thickness of Cd3As2, incident and azimuth angles are also clearly unveiled.

Two-dimensional natural hyperbolic materials: from polaritons modulation to applications.

Natural hyperbolic materials (HMs) in two dimensions (2D) have an extraordinarily high anisotropy and a hyperbolic dispersion relation. Some of them can even sustain hyperbolic polaritons with great directional propagation and light compression to deeply sub-wavelength scales due to their inherent anisotropy. Herein, the anisotropic optical features of 2D natural HMs are reviewed. Four hyperbolic polaritons (i.e., phonon polaritons, plasmon polaritons, exciton polaritons, and shear polaritons) as well as their generation mechanism are discussed in detail. The natural merits of 2D HMs hold promise for practical quantum photonic applications such as valley quantum interference, mid-infrared polarizers, spontaneous emission enhancement, near-field thermal radiation, and a new generation of optoelectronic components, among others. The conclusion of these analyses outlines existing issues and potential interesting directions for 2D natural HMs. These findings could spur more interest in anisotropic 2D atomic crystals in the future, as well as the quick generation of natural HMs for new applications.

Zn ion post-implantation-driven synthesis of CuZn alloy nanoparticles in Cu-preimplanted silica and their thermal evolution.

Cu nanoparticles (NPs) were fabricated in silica by 45 keV Cu ion implantation at a fluence of 1.0 × 10(17) cm(-2) and were then subjected to implantation of 50 keV Zn ions at fluences of 1.0 × 10(16), 5.0 × 10(16), and 10.0 × 10(16) cm(-2), respectively. Our results clearly show that post Zn ion implantation could significantly modify structures and components of the preformed Cu NPs and thus the corresponding surface plasmon resonance (SPR) absorption can be modulated in a wide range. In particular, CuZn alloy NPs with unique SPR absorption were synthesized in Cu-implanted silica followed by Zn ion implantation at a fluence of 5.0 × 10(16) cm(-2). During subsequent annealing, two distinguished processes concerning CuZn alloy NPs (i.e., realloying and dealloying) were found that directly result from thermally driven diffusion of Zn atoms. Moreover, owing to Zn diffusion, lots of core-shell nanostructures consisting of Zn-related compound shells around Cu cores were observed after annealing at 500 °C and higher. The underlying mechanism concerning the formation and decomposition of CuZn alloy NPs is discussed and presented.

[The impact of air temperature variation on the visits to emergency room in Shanghai].

OBJECTIVE: To assess the association between air temperature and emergency room visits among patients covered by medical care program from 'third-grade' hospitals in Shanghai. METHODS: Generalized additive model (GAM) was used to analyze time series, and AR(P) was used to deal with auto correlation of time series. After controlling factors as both medium-term and long-term trends, day of the week, vocation, typical pneumonia and pollutants, the association between air temperature and emergency room visits in virtue of quadratic curve and differential coefficient principle were estimated. RESULTS: When air temperature was below 14.71 degrees C, the increase of 95% confidence interval to relative risk in corresponding emergency room visits along with 1 degree C increase of air temperature, was less than 1. However, when air temperature was above 19.59 degrees C, the relative risk's 95% confidence interval was greater than 1. When air temperature varied at the range of 14.71 degrees C-19.59 degrees C, the 95% confidence interval of the relative risk would include 1. Hence, air temperature range between 14.71 degrees C-19.59 degrees C, was called the optimum temperature range. CONCLUSION: Our findings indicated that the current air temperature had an acute impact on the number of emergency room visits among patients covered by medical care program visiting those third grade hospitals in Shanghai.