Yakov M. Strelniker

Theory of optical transmission through elliptical nanohole arrays

We present a theory that explains (in the quasistatic limit) the experimentally observed [R. Gordon et al., Phys. Rev. Lett. 92, 037401 (2004)] squared dependence of the ratio of polarizations on the aspect ratio of the holes, as well as other features of extraordinary light transition. We calculated the effective dielectric tensor of a metal film penetrated by elliptical cylindrical holes and found the extraordinarily light transmission at special frequencies related to the surface plasmon resonances of the composite film. We also propose to use the magnetic field for getting a strong polarization effect, which depends on the ratio of the cyclotron to plasmon frequencies.

Percolation model for the superconductor-insulator transition in granular films

We study the temperature dependence of the superconductor-insulator transition in granular superconductors. Empirically, these systems are characterized by very broad resistance tails, which depend exponentially on the temperature, and the normal state resistance. We model these systems by two-dimensional random resistor percolation networks in which the resistance between two grains is governed either by Josephson junction coupling (Cooper pairs tunneling) or by quasiparticle tunneling. Our numerical simulations as well as an effective medium evaluation explain the experimental results over a wide range of temperatures and resistances. Using effective medium approximation we find an analytical expression for the effective resistance of the system and the value of the critical resistance separating conducting from insulating branches.

Resistance distribution in the hopping percolation model

We study the distribution function P (rho) of the effective resistance rho in two- and three-dimensional random resistor networks of linear size L in the hopping percolation model. In this model each bond has a conductivity taken from an exponential form sigma proportional to exp (-kappar) , where kappa is a measure of disorder and r is a random number, 0< or = r < or =1 . We find that in both the usual strong-disorder regime L/ kappa(nu) >1 (not sensitive to removal of any single bond) and the extreme-disorder regime L/ kappa(nu) <1 (very sensitive to such a removal) the distribution depends only on L/kappa(nu) and can be well approximated by a log-normal function with dispersion b kappa(nu) /L , where b is a coefficient which depends on the type of lattice, and nu is the correlation critical exponent.

Magneto-optical spaser

We present an electrodynamical model of a quantum plasmonic device--the magneto-optical (MO) spaser. It is shown that a spherical gain nanoparticle coated with a metallic MO shell can operate as a spaser amplifying circularly polarized surface plasmons. The MO spaser may be used in design of an optical isolator in plasmonic transmission lines as well as in spaser spectrometry of chiral molecules.

Recent advances in strong field magneto-transport in a composite medium

Macroscopic inhomogeneities have a profound effect on electrical conductivity in the presence of a strong magnetic field B. One expression of this is the appearance of a new physical length in the system, which increases with B and is unbounded. This length characterizes the extra distortions of the local current density which are produced by the strong Hall effect. In fractal clusters, different scaling behavior is found to occur at scales above and below this length. In random percolating systems, the new length competes with the percolation correlation length for dominance over the critical behavior. The divergence of each of these lengths is associated with a different fixed point. In metallic composites with a periodic microstructure, the new length is responsible for a strong anisotropy which appears in the magneto-resistance, even when the rotational symmetry is simple cubic or simple square.

Magneto-optical features and extraordinary light transmission through perforated metal films filled with liquid crystals

We calculate the effective dielectric tensor of a metal film penetrated by cylindrical holes filled with a nematic liquid crystal (NLC) whose director is parallel to the film and can be controlled by a static magnetic field whose direction can be rotated in an arbitrary direction in the plane of the film. We consider both randomly distributed holes (using a Maxwell-Garnett approximation) and a square lattice of holes (using a Fourier technique). Both the holes and the lattice constant of the square lattice are assumed small compared to the wavelength. The films are found to exhibit extraordinary light transmission at special frequencies, ωsp, related to the surface plasmon (SP) resonances of the composite film, which depends on the direction of the applied magnetic field.

High-Field Magnetotransport in a Percolating Medium

A discrete network model is used to discuss the critical behaviour of magnetotransport in a percolating medium in the presence of a magnetic field H of arbitrary strength. By applying a real-space renormalization group transformation, we find that there is strong magnetoresistance ρ(H) near the percolation threshold. We also find that there are two fixed points: one at p = pc and H = 0, and another at p = pc and H = ∞. The crossover between them is governed by a new, field-dependent length. In a percolating metal-insulator mixture, the resistivity ratio with and without a field ρ(H)/ρ(0) is predicted to saturate as p → pc at a value ~ H0.5.

High resolution Hall measurements across the VO2 metal-insulator transition reveal impact of spatial phase separation.

Many strongly correlated transition metal oxides exhibit a metal-insulator transition (MIT), the manipulation of which is essential for their application as active device elements. However, such manipulation is hindered by lack of microscopic understanding of mechanisms involved in these transitions. A prototypical example is VO2, where previous studies indicated that the MIT resistance change correlate with changes in carrier density and mobility. We studied the MIT using Hall measurements with unprecedented resolution and accuracy, simultaneously with resistance measurements. Contrast to prior reports, we find that the MIT is not correlated with a change in mobility, but rather, is a macroscopic manifestation of the spatial phase separation which accompanies the MIT. Our results demonstrate that, surprisingly, properties of the nano-scale spatially-separated metallic and semiconducting domains actually retain their bulk properties. This study highlights the importance of taking into account local fluctuations and correlations when interpreting transport measurements in highly correlated systems.

Magneto-optical response of a periodic metallic nano-structure

When an applied magnetic field has an arbitrary direction with respect to the lattice axes of a periodically nano-structured metal-dielectric metamaterial, the macroscopic or bulk effective permittivity tensor becomes anisotropic and all its components can be nonzero. This effect can be especially strong and significant in the vicinity of surface plasmon and cyclotron resonances (the frequencies of which are also sensitive to the value and direction of the applied external magnetic field). A similar effect for the case of dc effective conductivity is already verified experimentally (since magneto-conductivity tensor can be measured directly). However, this prediction for the permittivity has not yet been tested experimentally (since the permittivity tensor cannot be measured directly). What can be measured directly is the Voigt rotation, for which general exact analytical expressions were not published previously. In this work we have studied analytically and numerically the rotation and ellipticity of polarization of the light propagating through a metamaterial film with periodic nanostructure for arbitrary direction of the applied static magnetic field, including both Voigt and Faraday configurations. In the Voigt configuration we found a strong dependence of the above mentioned effects on the direction of the applied magnetic field.

Enhancement of the Faraday and Other Magneto-Optical Effects in Magnetophotonic Crystals

It is shown that for existent natural materials the Faraday rotation is far below the theoretical limit [Steel et al. in J. Lightwave Technol. 18:1297, 2000]. Under this condition the value of the Faraday rotation is primarily determined by the Q-factor, while the low group velocity value, multipass traveling and energy concentration in magneto-optical material play a secondary role. A comparative analysis of the efficiency of different schemes employing defect modes, Tamm surface states, the Borrmann effect and plasmon resonance is presented.