and absorb light with no diffraction. Planar metamaterials offer unprecedented fl exibility in the design and control of light propagation, replacing bulk optical components, [1][2][3][4][5] and exhibiting exotic optical effects, such as asymmetric transmission [ 6 ] and extrinsic optical activity, [ 7 ] whereas recent demonstrations of anomalous refl ection and refraction by metasurfaces have opened a new exciting chapter in photonic research. [ 8,9 ] Metasurfaces can be readily fabricated using existing planar technologies, while hybridization of their fabric with naturally available functional materials should enable dynamic control over their optical properties, dramatically expanding the range of potential metamaterial applications. [ 10,11 ] Among the existing functional materials, liquid crystals (LCs) possess arguably the strongest and most broadband optical non-linearity and birefringence, which can be externally controlled by temperature, light, and electric or magnetic fi elds. [ 12 ] That has made liquid crystals, and nematics in particular, one of the fi rst and most popular active ingredients considered for hybrid metamaterial and plasmonic designs. [13][14][15][16][17][18][19][20][21] Although the refractive index changes attainable in liquid crystals are extraordinarily large, the effi ciency of spectral tuning in the nematic phase may be reduced substantially due to strong surface anchoring of LC molecules. The latter, in fact, presents a serious problem for nanostructured LC-loaded metasurfaces operating in the visible and near-IR, and so far has made controlling the wavelength of their optical response practically impossible. [21][22][23] In this paper, we introduce a design of a near-IR active metasurface functionalized with a nematic LC, which allowed us to overcome the problem of strong anchoring and engage for the fi rst time the mechanism of electrically controlled nanoscale in-plane switching of the LC director. As a result, the resonant response of the demonstrated metamaterial hybrid could be controlled both in terms of its magnitude and wavelength with the spectral tunability approaching the theoretical limit of 9%. Active Metamaterial-LC Hybrid: Design and FabricationAlthough the in-plane LC switching has been experimentally demonstrated on the microscale for applications in LC Achieving an effi cient spectral tuning in liquid-crystal (LC)-loaded active photonic metamaterials has so far remained a challenge due to strong surface anchoring of LC molecules. This paper reports on a novel approach in the development of hybrid metamaterials that enables to overcome this problem and engage for the fi rst time in-plane switching of liquid-crystal molecules on the nanoscale. Combined with the usual volume switching, it unlocks the full potential of the liquid crystals as a functional component of active metamaterial hybrids operating at optical frequencies. As a result, the resonant response of an active metasurface can now be controlled both in terms of its magnitude and wavelength with the...

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We present a detailed experimental and theoretical study of the optical response of suspensions of ferromagnetic nanoparticles (''ferroparticles'') in nematic liquid crystals (''ferronematics''), concentrating on the magnetic field-induced Frederiks transition. Even extremely low ferroparticle concentrations (at a volume fraction between 2 Â 10 À5 and 2 Â 10 À4 ), induce a significant additional ferronematic linear response at low magnetic field (<100 G) and a decrease in the effective magnetic Frederiks threshold. The experimental results demonstrate that our system has weak ferronematic behavior. The proposed theory takes into account the nematic diamagnetism and assumes that the effective magnetic susceptibility, induced by the nanoparticles, no longer dominates the response. The theory is in good agreement with the experimental data for the lowest concentration suspensions and predicts the main features of the more concentrated ones. The deviations observed in these cases hint at extra effects due to particle aggregation, which we have also observed directly in photographs.

We experimentally demonstrate efficient electro-optical control in an active nano-structured plasmonic metamaterial hybridised with a liquid-crystal cell. The hybridisation was achieved by simultaneously replacing the polarizer, transparent electrode and molecular alignment layer of the liquid-crystal cell with the metamaterial nano-structure. With the control signal of only 7 V we have achieved a fivefold hysteresis-free modulation of metamaterial transmission at the wavelength of 1.55 µm.

We investigated the physical properties of low concentration ferroelectric nematic colloids, using calorimetry, optical methods, infrared spectroscopy and capacitance studies. The resulting colloids normally remain homogeneous, but the nematic orientational coupling is significantly amplified. In particular cases, the nematic orientation coupling increases by 10% for particle concentrations of 0.2%. A manifestation of the increased orientational order is that the clearing temperature of a nematic colloid increases up to 40 Celsius degrees compared to the pure LC host. A theoretical model is proposed in which the ferroelectric particles induce local dipoles whose effective interaction is proportional to the square of the orientational order parameter.PACS numbers: 64.70. Md, 82.70.Dd, Colloids in which the solute is liquid crystalline (LC) are known to possess an extremely rich set of behaviors [1,2,3,4,5]. The anchoring between the LC and microcolloidal particles ( 1µm) can produce long-range orientational distortions around the particles. This results in strong inter-particle interactions -sometimes repulsive and sometimes attractive -in the mesophase. The interactions can give rise to well-ordered structures of particles in the liquid crystal matrix (both lattices and chains) [2,3]. However, in most cases a prerequisite for interesting LC colloidal behavior has been a high concentration dispersion, typically with particle volume fraction c part 30%. In such systems aggregated particles produce director distortions extending over macroscopic scales. These suspensions scatter light strongly, and possess unique structural, mechanical, electro-and magneto-optical properties [5,6].Recently, we have shown that even at low concentrations (c part 1%), LC colloids differ strongly from the pure host material [7,8,9,10]. These colloids consist of submicron ferroelectric particles suspended in the LC host. In these systems, unlike in classic LC colloids, the suspensionmatrix interaction is insufficient to disturb the LC orientation. This small concentration dramatically increases the dielectric anisotropy, significantly decreases the Freedericksz transition voltage, and significantly accelerates electric field-induced director reorientation.In this letter, we report results which show that these phenomena are general properties of liquid crystal suspensions containing ferroelectric colloidal nanoparticles. The addition of impurities normally decreases the nematic clearing temperature T N I [11]. However, our measurements show massive increases in T N I , of the order of 40 • C, for mass impurity concentrations of the order of 0.2%. These results imply an increase in the effective nematic interaction parameter. Measurements of the birefringence, dielectric anisotropy and order parameter in the suspension are consistent with this picture.We have also constructed a theoretical model. The ferroelectric particles in the suspension produce large electric fields in their neighborhood. These electric fields produce induce...

To cite this article: E. Ouskova , O. Buchnev , V. Reshetnyak , Yu. Reznikov & H. Kresse (2003) Dielectric relaxation spectroscopy of a nematic liquid crystal doped with ferroelectric Sn 2 P 2 S 6 nanoparticles, Liquid Crystals, 30:10, It was found that doping a nematic liquid crystal (LC) with a small amount of ferroelectric nanoparticles strongly affects the dielectric properties of the system. In particular, adding the ferroelectric particles results in a shift of the absorption bands corresponding to the rotation of liquid crystal molecules around their short axes to lower frequencies and in an increase of the amplitude and with of the absorption bands. This suggests that strong interactions occur between the LC molecules and the particles, caused by the large dipole moment and high polarizability of the ferro-particles. The ferroelectric particles affect not only dielectric losses, but also dielectric permittivity of the system. Specifically, the static dielectric permittivity and the dielectric anisotropy of the suspension are more than twice that of the pure LC.

Functional materials based on ferroelectric, inorganic nanoparticles, and low refractive index nematic liquid crystals show strong induced birefringence and dielectric anisotropy. Birefringence can increase by a factor of 2 and dielectric anisotropy by a factor of 3 as compared with nominally pure liquid crystals. The enhancement of the electro-optic performance is higher in liquid crystals with Sn2P2S6 (SPS) nanoparticles than with BaTiO3 nanoparticles. The shape and size distribution of both types of ferroelectric particles were characterized using atomic force microscopy. The average size of SPS nanoparticles was 45nm and of BaTiO3 nanoparticles was 20nm.

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