We reveal an outstanding potential of water as an inexpensive, abundant and bio-friendly high-refractive-index material for creating tunable all-dielectric photonic structures and metamaterials. Specifically, we demonstrate thermal, mechanical and gravitational tunability of magnetic and electric resonances in a metamaterial consisting of periodically positioned water-filled reservoirs. The proposed water-based metamaterials can find applications not only as cheap and ecological microwave devices, but also in optical and terahertz metamaterials prototyping and educational lab equipment.
We study peculiarities of proximity effect in clean superconductor -ferromagnet structures caused by either spatial or momentum dependence of the exchange field. Even a small modulation of the exchange field along the quasiparticle trajectories is shown to provide a long range contribution to the supercurrent due to the specific interference of particle-and hole-like wave functions. The momentum dependence of the exchange field caused by the spin -orbit interaction results in the long -range superconducting correlations even in the absence of ferromagnetic domain structure and can explain the recent experiments on ferromagnetic nanowires.The exchange field h in ferromagnetic (F) metals is well known to destroy Cooper pairs resulting, thus, in a strong decay of superconducting (S) correlations in the F material and suppression of Josephson current in SFS junctions (see Refs. 1, 2 for review). Considering the quantum mechanics of quasiparticle excitations this destructive effect of the exchange field can be viewed as a consequence of a phase difference γ ∼ L/ξ h = 2Lh/ V F gained between the electron-and hole-like parts of the total wave function at the path of the length L. Both in the clean and dirty limits the measurable quantities should be calculated as superpositions of fast oscillating contributions e iγ from different trajectories and, thus, rapidly vanish with the increasing distance from the SF boundary.This textbook physical picture appears to be in sharp contrast with a number of recent experiments [3-8] which point to an anomalously large length of decay of superconducting correlations inside the F metal. As we can judge from the observation [8] of a noticeable supercurrent through a Co nanowire, this decay length can be of the order of half a micrometer which well exceeds typical coherence lengths in ferromagnets both in the clean and dirty limits. In the dirty limit such strong proximity effect can hardly be explained even taking account of long-range triplet correlations [2] induced by the exchange field inhomogeneity.Naturally, the inhomogeneity of the field h caused by the ferromagnetic domain structure can improve the conditions of Cooper pair survival in the clean limit as well. To suppress the destructive trajectory interference mentioned above the domain structure should cancel the phase gain γ for a certain group of quasiparticle trajectories. A simple example of such phase gain compensation can be realized in a clean junction consisting of two F layers with opposite orientations of magnetic moment [9,10]. On the other hand in the diffusive limit this compensation effect vanishes [11]. Note, that the exchange field inhomogeneity along the quasiclassical trajectory experiencing multiple reflections from the ferromagnet surface can appear even in the absence of the spatial domain structure. Indeed, the exchange field acting on band electrons in a solid with a finite spin -orbit interaction should obviously depend on the quasiparticle momentum [12]: h = h(k). The normal quasiparticle reflection...
Stealthy hyperuniform point patterns are characterized by a vanishing spatial Fourier transform around the origin of the reciprocal vector space. The long-range point density fluctuations are suppressed as well in materials consisting of such distribution of scatterers, opening up opportunities to control waves. Beside wave transport in such structured materials are driven by several elements, such as the acoustic properties of the host material, the scatterer characteristics, i.e., dimensions or resonant features, and the scatterer distribution patterns. The effects of these three basic elements on the wave transport properties are usually hard to discriminate. In this work, we analyze the transport properties of acoustic waves in one-dimensional phononic materials constituted of either non-resonant or resonant scatterers distributed along stealthy hyperuniform patterns in air. The pattern is controlled by the stealthiness, allowing us to continuously vary from random phononic materials to phononic crystals. The properties of the scatterers are controlled by their size and/or the resonant frequencies. The properties of the host material are controlled by the viscothermal losses. Transport properties of stealthy hyperuniform materials are found to be robust to both the scatterer dimensions and inherent viscothermal losses, while strongly affected by the scatterer resonances, which introduce sharp dips in the transmission coefficient.
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