Isotropic materials are required to adhere to various mechanical principles due to their limited thermal stability. For instance, it is essential for Poisson's ratio to be within the range of -1 to 0.5, and the longitudinal wave velocity must exceed the transverse wave velocity.
View Article and Find Full Text PDFProc Natl Acad Sci U S A
March 2022
The origin of water on the Earth is a long-standing mystery, requiring a comprehensive search for hydrous compounds, stable at conditions of the deep Earth and made of Earth-abundant elements. Previous studies usually focused on the current range of pressure-temperature conditions in the Earth's mantle and ignored a possible difference in the past, such as the stage of the core-mantle separation. Here, using ab initio evolutionary structure prediction, we find that only two magnesium hydrosilicate phases are stable at megabar pressures, α-Mg_{2}SiO_{5}H_{2} and β-Mg_{2}SiO_{5}H_{2}, stable at 262-338 GPa and >338 GPa, respectively (all these pressures now lie within the Earth's iron core).
View Article and Find Full Text PDFWe study the diffraction of optical waves by a single layer of gyromagnetic cylinders. We show that a nonvanishing rotating dipole momentum is excited in a single gyromagnetic cylinder because of the classic analog of the Zeeman effect on photonic angular momentum states (PAMSs). Consequently, different collective dipole modes are excited in a gyromagnetic cylinder array at opposite incident angles.
View Article and Find Full Text PDFWe propose a novel scheme in realizing tunable slow-light performance by manipulating dark photonic angular momentum states (PAMSs) in metamaterials via the magneto-optical effect. We show that by applying a static magnetic field B, some pairs of sharp transmission dips can be observed in the background transparency window of a complex metamaterial design. Each pair of transmission dips are related to the excitation of dark PAMSs with opposite topological charges -m and +m, with a lifted degeneracy due to the classic analogue of Zeeman effect.
View Article and Find Full Text PDFComplex metamaterials with multiple optical resonances in constituent elements possess many similarities with open quantum systems that can be described by non-Hermitian Hamiltonian. By analogy with a two-state open quantum system, we show that a classic analogue of exceptional points can be observed in the transmission spectra of dual subwavelength metallic gratings. Anti-crossing (crossing) between the two branches λ(R) of extraordinary optical transmission, with crossing (anti-crossing) of the corresponding widths Γ(R), is observed in the parameter space spanned by the lateral displacement L and the angle of incidence φ0.
View Article and Find Full Text PDFMagneto-optical (MO) effect can break the reciprocal propagation of an optical wave along a MO-metal interface. We show that this nonreciprocal property also influences the guided modes in metal-MO-metal waveguides. Especially, the field profiles of the guided modes are neither symmetric nor anti-symmetric, but asymmetric.
View Article and Find Full Text PDFA photonic angular momentum state (PAMS) with a topological charge of m≠±1 is dipole forbidden at all polarizations of free-space incidence due to the existence of a unique helical phase. We show that by indirectly exciting dark PAMSs through coupling with a bright resonant element, a sharply variant transmission behavior and strong dispersion can be achieved. This behavior can subsequently be utilized in slow light.
View Article and Find Full Text PDFThe Gouy phase shift of optical beams in anisotropic indefinite metamaterials displays extraordinary characteristics because of the presence of anisotropic magnetic and electric responses. We propose a simple interpretation of these characteristics from the unusual dispersion relation of the optical waves in the metamaterials, which influences the expectation value of the axial propagation constant of the focused beam.
View Article and Find Full Text PDFMetamaterials have shown to support the intriguing phenomenon of asymmetric electromagnetic transmission in the opposite propagation directions, for both circular and linear polarizations. In the present article, we propose a criterion on the relationship among the elements of transmission matrix, which allows asymmetrical transmission for linearly polarized electromagnetic radiation only while the reciprocal transmission for circularly one. Asymmetric hybridized metamaterials are shown to satisfy this criterion.
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