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News Article | January 18, 2016
Site: www.materialstoday.com

A two-dimensional meta material composed of silver elements will have a negative refractive index for light in the most energetic region of the visible spectrum, 400 to 500 nanometers (violet, blue and light blue), according to computer simulations by the team of Sergey Belan, Vladimir Parfenyev, and Sergey Vergeles from the Landau Institute for Theoretical Physics in the Russian Academy of Sciences, Moscow; Belan is also affiliated with the Moscow Institute of Physics and Technology, in Dolgoprudny. Writing in the journal Optical Material Express, the researchers hint at its potential for compact optical. [DOI: 10.1364/OME.5.002843] The computations using the COMSOL Multiphysics package on a two-dimensional meta lattice composed of pairs of closely spaced silver cylinders with a radius of the order of 100 nanometers suggest a refractive efficiency of 70 percent and a reflective efficiency of 80 percent for violet to blue light. Earlier meta materials are usually three-dimensional and have much more complex geometries. Moreover, they have been demonstrated to operate at microwave wavelengths, which limits their potential applications. The silver lattice meta material works through diffraction, splitting incident light into rays depending on angle of incidence, wavelength and the period of the lattice. The structure of the unit cell determines how the energy of the incident light is distributed between the rays. In a material with a negative refractive index, all but one of the diffracted rays are suppressed and the remainder emerges in the desired direction. That direction is counterintuitive given our experience with the appearance of a stick dipped into a swimming pool where water has a natural, positive refractive index. At the mechanistic level, light's interaction with the pairs of metal cylinders is due to a plasmon resonance effect. The researchers have demonstrated that the extraordinary optical response of the proposed material arises due to excitation of the plasmonic modes in the gaps between cylinders, Belan told Materials Today. Tweaking the lattice allows a negative refractive index to be manifest for wide range of angles of incidence. This suggests potential applications in controlling signals in ultra-compact devices for optical telecommunications and future computing. The next step will be to manufacture with very high tolerance the requisite smooth metal cylinders with their less than 10 nanometer separation for laboratory testing of the meta material's true potential. "We are now working on optimization of the proposed design in order to improve efficiency," Belan told us. "Specifically, we are testing in simulations the metal rods with a non-circular cross-section. In addition, we are looking for collaboration with experimental groups capable of realizing negative refraction in the laboratory." David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".


Falkovsky L.A.,Landau Institute for Theoretical Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

The effects of phonon anharmonicity, phonon-magnon, and electron-phonon interactions on the temperature dependence of Raman optical phonon modes are theoretically investigated. Besides the Klemens result for the phonon width due to anharmonicity, the corresponding line shift is derived. We argue that the phonon decay into two magnons has very low intensity in ferromagnets with low Curie temperatures. Therefore, the electron interband transitions accompanied with the ferromagnetic ordering are included in considerations to get a good quantitative agreement with experiments. © 2013 American Physical Society.


Menshutin A.,Landau Institute for Theoretical Physics
Physical Review Letters | Year: 2012

We present a self-consistent picture of diffusion limited aggregation (DLA) growth based on the assumption that the probability density P(r,N) for the next particle to be attached within the distance r to the center of the cluster is expressible in the scale-invariant form P[r/R dep(N)]. It follows from this assumption that there is no multiscaling issue in DLA and there is only a single fractal dimension D for all length scales. We check our assumption self-consistently by calculating the particle-density distribution with a measured P(r/R dep) function on an ensemble with 1000 clusters of 5×107 particles each. We also show that a nontrivial multiscaling function D(x) can be obtained only when small clusters (N<10000) are used to calculate D(x). Hence, multiscaling is a finite-size effect and is not intrinsic to DLA. © 2012 American Physical Society.


Falkovsky L.A.,Landau Institute for Theoretical Physics
Journal of Experimental and Theoretical Physics | Year: 2012

The optical conductivity of graphene, bilayer graphene, and graphite in quantizing magnetic fields is studied. Both dynamical conductivities, longitudinal and Hall's, are evaluated analytically. The conductivity peaks are explained in terms of electron transitions. Correspondences between the transition frequencies and the magneto-optical features are established using the theoretical results. We show that trigonal warping can be considered within the perturbation theory for strong magnetic fields larger than 1 T. The semiclassical approach is applied for weak fields when the Fermi energy is much larger than the cyclotron frequency. The main optical transitions obey the selection rule with Δn = 1 for the Landau number n, but the Δn = 2 transitions due to the trigonal warping are also possible. The Faraday/Kerr rotation and light transmission/reflection in quantizing magnetic fields are calculated. Parameters of the Slonczewski-Weiss-McClure model are used in the fit taking the previous de Haas-van Alphen measurements into account and correcting some of them in the case of strong magnetic fields. © 2012 Pleiades Publishing, Ltd.


Lebed A.G.,University of Arizona | Lebed A.G.,Landau Institute for Theoretical Physics
Physical Review Letters | Year: 2011

We solve a long-standing problem about a theoretical description of the upper critical magnetic field, parallel to conducting layers and perpendicular to conducting chains, in a (TMTSF)2ClO4 superconductor. In particular, we explain why the experimental upper critical field, Hc2b ′6T, is higher than both the quasiclassical upper critical field and the Clogston paramagnetic limit. We show that this property is due to the coexistence of the hidden reentrant and Larkin-Ovchinnikov-Fulde-Ferrell phases in a magnetic field in the form of three plane waves with nonzero momenta of the Cooper pairs. Our results are in good qualitative and quantitative agreement with the recent experimental measurements of Hc2b′ and support a singlet d-wave-like scenario of superconductivity in (TMTSF) 2ClO4. © 2011 American Physical Society.


Lashkevich M.,Landau Institute for Theoretical Physics
Journal of Physics A: Mathematical and Theoretical | Year: 2012

The notion of operator resonances was previously introduced by Al Zamolodchikov within the framework of the conformal perturbation theory. The resonances are related to logarithmic divergences of integrals in the perturbation expansion, and manifest themselves in poles of the correlation functions and form factors of local operators considered as functions of conformal dimensions. The residues of the poles can be computed by means of some operator identities. Here, we study the resonances in the Liouville, sinh- and sine-Gordon models, considered as perturbations of a massless free boson. We show that the well-known higher equations of motion discovered by Al Zamolodchikov in the Liouville field theory are nothing but resonance identities for some descendant operators. The resonance expansion in the vicinity of a resonance point provides a regularized version of the corresponding operators. We try to construct the corresponding resonance identities and resonance expansions in the sinh- and sine-Gordon theories. In some cases it can be done explicitly, but in most cases we are only able to obtain a general form so far. We show nevertheless that the resonances are perturbatively exact, which means that each of them only appears in a single term of the perturbation theory. © 2012 IOP Publishing Ltd.


News Article | February 15, 2017
Site: www.eurekalert.org

Igor Kolokolov and Vladimir Lebedev, scientific experts from HSE's Faculty of Physics and the Landau Institute for Theoretical Physics of Russian Academy of Sciences, have developed an analytical theory, which binds the structure of coherent vortices formed due to inverse cascades in 2-D turbulence with the statistical properties of hydrodynamic fluctuations. Uncovering this link can be useful in identifying the causes of the particular characteristics of such atmospheric phenomena as cyclones and anticyclones. Their research is presented in an article published in the Journal of Fluid Mechanics. According to Vladimir Lebedev, one of the article's authors, 'this concerns how order comes out of chaos,' noting: 'we were able to generate analytical scheme, which, explains the results of numerical and laboratory experiments where coherent vortices (stable vortex formations) are observed by relating vortex characteristics to the statistical properties of chaotic fluctuations.' The article 'Velocity Statistics Inside Coherent Vortices Generated by the Inverse Cascade of 2-D Turbulence', published in the Journal of Fluid Mechanics, presents a consistent analytical theory, which describes both the intensive mean flow inside the vortices and the fluctuations therein. Namely, the research indicates that the vortices possess a universal structure, when there is an interval, the azimuth speed does not depend on distance from the vortex center. Statistical properties of the fluctuations in the universal interval are established. They can be used, for instance, to determine advection and mixing of pollutants in the turbulent flow. In short, the theory developed helps to explain the outcomes of laboratory experiments and numerical modelling of 2-D turbulence where coherent vortices had earlier been observed. The scientists note that this research does not rely on semiempirical formulae, whereby general conclusions are made about computational and natural experiments, but rather the correlations derived from first principles. The results of the analysis are valuable owing to their predictive power, as well as insight into such phenomena. Furthermore, the article presents the latest results of the scientists' efforts to analyze coherent vortices in 2-D turbulence, which the authors have been investigating for more than a decade. As both Kolokolov and Lebedev note, despite the fact that geophysics is much richer than fluid-film hydrodynamics, there are grounds to consider large-scale atmospheric phenomena such as cyclones, anticyclones and hurricanes as coherent structures that emerge out of 'chaos'. This, in turn, enriches our understanding of the laws controlling appearance of such atmospheric phenomena. Furthermore, this may, over the long-term, even offer us with possibilities to manage the phenomena.


The results of computer simulations carried out by the authors showed that it would be a high performance material for light with a wavelength from 400-500nm (violet, blue and light blue). Efficiency in this case is defined as the percentage of light scattered in a desired direction. The efficiency of the material is approximately 70 percent for refraction, and 80 percent for reflection of the light. Theoretically, the efficiency could reach 100 percent, but in real metals, there are losses due to ohm resistance. A metamaterial is a material, the properties of which are created by an artificial periodic structure. The prefix "meta" (from the Greek μετά - beyond) indicates that the characteristics of the material are beyond what we see in nature. Most often, when we talk about metamaterials, we mean materials with a negative refractive index. When light is incident on the surface of such a material, the refracted light is on the same side of the normal to the surface as the incident light. The difference between the behaviour of the light in a medium with a positive and a negative refractive index can be seen, for example, when a rod is immersed in liquid. The existence of substances with a negative refractive index was predicted as early as the middle of the 20th century. In 1976, Soviet physicist V.G. Veselago published an article that theoretically describes their properties, including unusual refraction of light. The term "metamaterials" for such substances was suggested by Roger Walser in 1999. The first samples of metamaterials were made from arrays of thin wires and only worked with microwave radiation. Importantly, the unusual optical effects do not necessarily imply the use of the volumetric (3d) metamaterials. You can also manipulate the light with the help of two-dimensional structures—so-called metasurfaces. In fact, it is a thin film composed of individual elements. The principle of operation of the metasurface is based on the phenomenon of diffraction. Any flat periodic array can be viewed as a diffraction lattice, which splits the incident light into a few rays. The number and direction of the rays depends on geometrical parameters: the angle of incidence, wavelength and the period of the lattice. The structure of the unit cell, in turn, determines how the energy of the incident light is distributed between the rays. For a negative refractive index, it is necessary that all but one of the diffraction rays are suppressed, then all of the incident light will be directed in the required direction. This idea underlies the recent work by the group of scientists from the Moscow Institute of Physics and Technology and the Landau Institute for Theoretical Physics. The unit cell of the proposed lattice is composed of a pair of closely spaced silver cylinders with a radius of the order of 100 nanometres (see figure). Such a structure is simple and operates at optical wavelengths, while most analogues have more complex geometries and only work with microwaves. The effective interaction of pairs of metal cylinders with light is due to the plasmon resonance effect. Light is absorbed by the metal rods, forcing the electrons in the metal to oscillate and re-radiate. Researchers were able to adjust the parameters of the cell so that the resulting optical lattice response is consistent with abnormal (i.e. negative) refraction of the incident wave (see figure). Interestingly, by reversing the orientation of the cylinder pairs you can get an abnormal reflection effect. It should be noted that the scheme works with a wide range of angles of incidence. These results can be applied to control optical signals in ultra-compact devices. In this case, we are talking primarily about optical transmission and information processing technologies, which will help expedite computer processing in the future. The conventional electrical interconnects used in modern chips are operating at the limit of their carrying capacities and inhibit further growth in computing performance. To replace the electrical interconnects by optical we need to effectively control optical signals at nanoscale. In order to solve this problem, the efforts of the scientific community are focused to a large extent on creating structures capable of redirecting the light toward the desired direction. It should be noted that an experimental demonstration of anomalous scattering using the lattice described above requires the manufacture of smooth metal cylinders separated by a very small distance (less than 10 nanometres). This is quite a difficult practical problem, the solution of which could be a breakthrough for modern photonics. Explore further: Bending light the 'wrong' way


News Article | February 15, 2017
Site: phys.org

Igor Kolokolov and Vladimir Lebedev, scientific experts from HSE's Faculty of Physics and the Landau Institute for Theoretical Physics of Russian Academy of Sciences, have developed an analytical theory binding the structure of coherent vortices formed due to inverse cascades in 2-D turbulence with the statistical properties of hydrodynamic fluctuations. Uncovering this link could be useful in identifying the causes of the particular characteristics of such atmospheric phenomena as cyclones and anticyclones. Their research is presented in an article published in the Journal of Fluid Mechanics. According to Vladimir Lebedev, one of the article's authors, 'This concerns how order comes out of chaos,' noting, 'we were able to generate an analytical scheme explaining the results of numerical and laboratory experiments where coherent vortices (stable vortex formations) are observed by relating vortex characteristics to the statistical properties of chaotic fluctuations.' The article, 'Velocity Statistics Inside Coherent Vortices Generated by the Inverse Cascade of 2-D Turbulence', published in the Journal of Fluid Mechanics, presents a consistent analytical theory describing both the intensive mean flow inside the vortices and the fluctuations therein. Namely, the research indicates that the vortices possess a universal structure: When there is an interval, the azimuth speed does not depend on distance from the vortex center. Statistical properties of the fluctuations in the universal interval are established. They can be used, for instance, to determine advection and mixing of pollutants in the turbulent flow. In short, the theory helps to explain the outcomes of laboratory experiments and numerical modelling of 2-D turbulence where coherent vortices had earlier been observed. The scientists note that this research does not rely on semiempirical formulae, whereby general conclusions are made about computational and natural experiments, but rather the correlations derived from first principles. The results of the analysis are valuable owing to their predictive power, as well as insight into such phenomena. Furthermore, the article presents the latest results of the scientists' efforts to analyze coherent vortices in 2-D turbulence, which the authors have been investigating for more than a decade. As both Kolokolov and Lebedev note, despite the fact that geophysics is much richer than fluid-film hydrodynamics, there are grounds to consider large-scale atmospheric phenomena such as cyclones, anticyclones and hurricanes as coherent structures that emerge out of 'chaos'. This, in turn, enriches our understanding of the laws controlling appearance of such atmospheric phenomena. Furthermore, this may, over the long-term, even offer us with possibilities to manage the phenomena. Explore further: Physicists generate ocean vortices in a glass of water More information: I. V. Kolokolov et al, Velocity statistics inside coherent vortices generated by the inverse cascade of 2-D turbulence, Journal of Fluid Mechanics (2016). DOI: 10.1017/jfm.2016.699


Home > Press > A new metamateria will speed up computers: Scientists have proposed a metasurface for the anomalous scattering of visible light Abstract: A new metamaterial with an unusual refraction of light will speed up computers. A team of scientists from the Moscow Institute of Physics and Technology (MIPT) and the Landau Institute for Theoretical Physics in the Russian Academy of Sciences has proposed a two-dimensional metamaterial composed of silver elements, that refracts light in an unusual way. The research has been published on Nov. 18, 2015 in Optical Material Express. In the future, these structures will be able to be used to develop compact optical devices, as well as to create an 'invisibility cloak.' The results of computer simulations carried out by the authors showed that it would be a high performance material for light with a wavelength from 400-500nm (violet, blue and light blue). Efficiency in this case is defined as the percentage of light scattered in a desired direction. The efficiency of the material is approximately 70% for refraction, and 80% for reflection of the light. Theoretically, the efficiency could reach 100%, but in real metals there are losses due to ohm resistance. A metamaterial is a material, the properties of which are created by an artificial periodic structure. The prefix 'meta' (from the Greek μετ? -- beyond) indicates that the characteristics of the material are beyond what we see in nature. Most often, when we talk about metamaterials, we mean materials with a negative refractive index. When light is incident on the surface of such a material, the refracted light is on the same side of the normal to the surface as the incident light. The difference between the behaviour of the light in a medium with a positive and a negative refractive index can be seen, for example, when a rod is immersed in liquid. The existence of substances with a negative refractive index was predicted as early as the middle of the 20th century. In 1976 Soviet physicist V.G. Veselago published an article that theoretically describes their properties, including an unusual refraction of light. The term 'metamaterials' for such substances was suggested by Roger Walser in 1999. The first samples of metamaterials were made from arrays of thin wires and only worked with microwave radiation. Importantly, the unusual optical effects do not necessarily imply the use of the volumetric (3d) metamaterials. You can also manipulate the light with the help of two-dimensional structures -- so-called metasurfaces. In fact, it is a thin film composed of individual elements. The principle of operation of the metasurface is based on the phenomenon of diffraction. Any flat periodic array can be viewed as a diffraction lattice, which splits the incident light into a few rays. The number and direction of the rays depends on geometrical parameters: the angle of incidence, wavelength and the period of the lattice. The structure of the unit cell, in turn, determines how the energy of the incident light is distributed between the rays. For a negative refractive index it is necessary that all but one of the diffraction rays are suppressed, then all of the incident light will be directed in the required direction. This idea underlies the recent work by the group of scientists from the Moscow Institute of Physics and Technology and the Landau Institute for Theoretical Physics. The unit cell of the proposed lattice is composed of a pair of closely spaced silver cylinders with a radius of the order of 100 nanometres (see figure). Such a structure is simple and operates at optical wavelengths, while most analogues have more complex geometries and only work with microwaves. The effective interaction of pairs of metal cylinders with light is due to the plasmon resonance effect. Light is absorbed by the metal rods, forcing the electrons in the metal to oscillate and re-radiate. Researchers were able to adjust the parameters of the cell so that the resulting optical lattice response is consistent with abnormal (i.e. negative) refraction of the incident wave (see figure). Interestingly, by reversing the orientation of the cylinder pairs you can get an abnormal reflection effect. It should be noted that the scheme works with a wide range of angles of incidence. The results achieved can be applied to control optical signals in ultra-compact devices. In this case we are talking primarily about optical transmission and information processing technologies, which will help expedite computer processing in the future. The conventional electrical interconnects used in modern chips are operating at the limit of their carrying capacities and inhibit further growth in computing performance. To replace the electrical interconnects by optical we need to be able to effectively control optical signals at nanoscale. In order to solve this problem the efforts of the scientific community are focused to a large extent on creating structures capable of 'turning' the light in the desired direction. It should be noted that an experimental demonstration of anomalous scattering using the lattice described above requires the manufacture of smooth metal cylinders separated by a very small distance (less than 10 nanometres). This is quite a difficult practical problem, the solution of which could be a breakthrough for modern photonics. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

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