Spin canting induced large nonreciprocal Goos-Hänchen shifts

Recent studies on surface reflection illustrate how light beams can be laterally shifted from the position predicted by geometrical optics, the so called Goos-Hänchen effect. In antiferromagnets this shifts can be controlled with an external magnetic field. We show that a configuration in which spins cant in response to applied magnetic fields enhance possibilities of field controlled shifts. Moreover, we show that nonreciprocal displacements are possible, for both oblique and normal incidence, due to inherent nonreciprocity of the polariton phase with respect to the propagation direction. In the absence of an external field, reciprocal displacements occur

Tunable all-angle negative refraction using antiferromagnets

We show how all-angle negative refraction can occur in a uniaxial antiferromagnet close to the magnon resonance frequency. This behavior is based on the fact that, in such cases, the antiferromagnet acts as an indefinite permeability medium, i.e., not all its permeability tensor components are of the same sign. If an external magnetic field is applied, the angle of refraction becomes tunable, and can be made to change sign. We illustrate these effects using the example of MnF 2 at low temperature, and show that in this system negative refraction should occur with a large figure of merit

Tunable optical effects in natural hyperbolic magnetic media

Anisotropic media have been the object of study in the fields of optics and photonics for decades. More recently, we have seen the emergence of a new class of anisotropic materials, the so-called hyperbolic media. These new structures rapidly gained attention for displaying several optical effects such as all-angle negative refraction with low loss. This thesis presents a theoretical investigation of anisotropic magnetic crystals working as hyperbolic media. These type of structures are not often associated with hyperbolic behaviour. The aim is to show that magnetic crystals are not only an alternative way to obtain hyperbolic dispersion but that they can also be controlled by externally applied fields. The general theory is applied to manganese fluoride (MnF2), a reasonably well studied antiferromagnet, in a configuration in which spins cant in response to applied magnetic fields. The work can be divided into three main strands. The first is to treat the surface reflection and illustrate how light beams can be laterally shifted from the position predicted by geometrical optics i.e., the so called Goos-Hänchen effect. In antiferromagnets these shifts can be controlled with an external magnetic field. Moreover, the possibility of nonreciprocal displacements is investigated, for both oblique and normal incidence, due to an inherent nonreciprocity of the polariton phase with respect to the propagation direction. Reciprocal displacements are also studied in the absence of an external field. The second strand of the work is a study of how all-angle negative refraction can occur in a uniaxial antiferromagnet close to the magnon resonance frequency. This behavior is based on the fact that, in such cases, the antiferromagnet acts as an indefinite permeability medium, i.e., not all its permeability tensor components are of the same sign. If an external magnetic field is applied, the angle of refraction becomes tunable, and can be made to change sign. The final part of this work proposes tunable slab lensing in natural magnetic media using an externally applied magnetic field. Natural hyperbolic magnetic materials not only display imaging obtained from slab lenses with plane parallel sides but also allow one to modify the focal length of a slab lens with an externally applied magnetic field. This is possible because antiferromagnets are gyrotropic and support magnetic polaritons whose frequencies are sensitive to magnetic fields. In addition, an investigation of the caustic formation in this type of lenses is presented for low temperatures, when damping should be small. Slab focusing is also studied at higher temperatures

Apparent ferromagnetism in the 'pinwheel' artificial spin ice

Magnetic artificial spin ice provides examples of how competing interactions between magnetic nanoelements can lead to a range of fascinating and unusual phenomena. We examine theoretically a class of spin ice tilings, called pinwheel, for which near degeneracy of spin configuration energies can be achieved. The pinwheel tiling is a simple but crucial variant on the square ice geometry, in which each nanoelement of square ice is rotated some angle about its midpoint. Surprisingly, this rotation leads to an intriguing phase transition; and even though the spins are not parallel to one another, a ferromagnetic phase is found for rotation angles near 45∘. Here, magnetic domains and domain walls are found when viewed in terms of net magnetisation. Moreover, the ferromagnetic behaviour of the system depends on its anisotropy which we can control by array shape and size

Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz

We examine the possibility of using negative refraction stemming from the phonon response in an anisotropic crystal to create a simple slab lens with plane parallel sides, and show that imaging from such a lens should be possible at room temperature despite the effects of absorption that are inevitably present due to phonon damping. In particular, we consider the case of crystal quartz, a system for which experimental measurements consistent with all-angle negative refraction have already been demonstrated. Furthermore, we investigate the possibility of subwavelength imaging from such materials, and show that it should be possible for certain configurations.Comment: 12 pages, 10 figure

Turbulence Hierarchy in a Random Fibre Laser

Turbulence is a challenging feature common to a wide range of complex phenomena. Random fibre lasers are a special class of lasers in which the feedback arises from multiple scattering in a one-dimensional disordered cavity-less medium. Here, we report on statistical signatures of turbulence in the distribution of intensity fluctuations in a continuous-wave-pumped erbium-based random fibre laser, with random Bragg grating scatterers. The distribution of intensity fluctuations in an extensive data set exhibits three qualitatively distinct behaviours: a Gaussian regime below threshold, a mixture of two distributions with exponentially decaying tails near the threshold, and a mixture of distributions with stretched-exponential tails above threshold. All distributions are well described by a hierarchical stochastic model that incorporates Kolmogorov's theory of turbulence, which includes energy cascade and the intermittence phenomenon. Our findings have implications for explaining the remarkably challenging turbulent behaviour in photonics, using a random fibre laser as the experimental platform.Comment: 9 pages, 5 figure

Microscopic origin of level attraction for a coupled magnon-photon system in a microwave cavity

We discuss various microscopic mechanisms for level attraction in a hybridized magnon-photon system of a ferromagnet in a microwave cavity. The discussion is based upon the electromagnetic theory of continuous media where the effects of the internal magnetization dynamics of the ferromagnet are described using dynamical response functions. This approach is in agreement with quantized multi-oscillator models of coupled photon-magnon dynamics. We demonstrate that to provide the attractive interaction between the modes, the effective response functions should be diamagnetic. Magneto-optical coupling is found to be one mechanism for the effective diamagnetic response, which is proportional to photon number. A dual mechanism based on the Aharonov-Casher effect is also highlighted, which is instead dependent on magnon number. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.Ministry of Education and Science of the Russian Federation, Minobrnauka: MK-1 731.2018.2The authors thank Can-Min Huand Michael Harder for stimulating discussions. IP is supported by the Ministry of Education and Science of the Russian Federation, Grant No. MK-1 731.2018.

Resposta do dendezeiro à aplicação de fertilizantes nas condições do Estado do Amazonas.

O presente trabalho visa estudar o efeito da adubação nitrogenada, fosfatada, potássica e magnesiana no desenvolvimento e na produção do dendezeiro.bitstream/item/89200/1/PA-08-Maria-do-Rosario.pd

A reversible system based on hybrid toggle radius-4 cellular automata and its application as a block cipher

The dynamical system described herein uses a hybrid cellular automata (CA) mechanism to attain reversibility, and this approach is adapted to create a novel block cipher algorithm called HCA. CA are widely used for modeling complex systems and employ an inherently parallel model. Therefore, applications derived from CA have a tendency to fit very well in the current computational paradigm where scalability and multi-threading potential are quite desirable characteristics. HCA model has recently received a patent by the Brazilian agency INPI. Several evaluations and analyses performed on the model are presented here, such as theoretical discussions related to its reversibility and an analysis based on graph theory, which reduces HCA security to the well-known Hamiltonian cycle problem that belongs to the NP-complete class. Finally, the cryptographic robustness of HCA is empirically evaluated through several tests, including avalanche property compliance and the NIST randomness suite.Comment: 34 pages, 12 figure