Search results for "Wave"
showing 10 items of 6009 documents
Programmable linear quantum networks with a multimode fibre
2019
Reconfigurable quantum circuits are fundamental building blocks for the implementation of scalable quantum technologies. Their implementation has been pursued in linear optics through the engineering of sophisticated interferometers. While such optical networks have been successful in demonstrating the control of small-scale quantum circuits, scaling up to larger dimensions poses significant challenges. Here, we demonstrate a potentially scalable route towards reconfigurable optical networks based on the use of a multimode fibre and advanced wavefront-shaping techniques. We program networks involving spatial and polarisation modes of the fibre and experimentally validate the accuracy and ro…
Fluctuating Interfaces in Liquid Crystals
2008
We review and compare recent work on the properties of fluctuating interfaces between nematic and isotropic liquid-crystalline phases. Molecular dynamics and Monte Carlo simulations have been carried out for systems of ellipsoids and hard rods with aspect ratio 15:1, and the fluctuation spectrum of interface positions (the capillary wave spectrum) has been analyzed. In addition, the capillary wave spectrum has been calculated analytically within the Landau-de Gennes theory. The theory predicts that the interfacial fluctuations can be described in terms of a wave vector dependent interfacial tension, which is anisotropic at small wavelengths (stiff director regime) and becomes isotropic at l…
Magnetic anisotropy in Fe/U and Ni/U bilayers
2021
Magnetometry measurements of Fe/U and Ni/U bilayer systems reveal a non-monotonic dependence of the magnetic anisotropy for U thicknesses in the range 0 nm - 8 nm, with the Fe/U bilayers showing a more prominent effect as compared to Ni/U. The stronger response for Fe/U is ascribed to the stronger 3d-5f hybridization of Fe and U. This non-monotonic behaviour is thought to arise from quantum well states in the uranium overlayers. Estimating an oscillation period from the non-monotonic data, and comparing it to Density Functional Theory calculations, we find that wavevector matches to the experimental data can be made to regions of high spectral density in (010) and (100) cuts of the electron…
Application of elastostatic Green function tensor technique to electrostriction in cubic, hexagonal and orthorhombic crystals
2002
The elastostatic Green function tensor approach, which was recently used to treat electrostriction in numerical simulation of domain structure formation in cubic ferroelectrics, is reviewed and extended to the crystals of hexagonal and orthorhombic symmetry. The tensorial kernels appearing in the expressions for effective nonlocal interaction of electrostrictive origin are derived explicitly and their physical meaning is illustrated on simple examples. It is argued that the bilinear coupling between the polarization gradients and elastic strain should be systematically included in the Ginzburg-Landau free energy expansion of electrostrictive materials.
Time-resolved imaging of pulse-induced magnetization reversal with a microwave assist field
2015
AbstractThe reversal of the magnetization under the influence of a field pulse has been previously predicted to be an incoherent process with several competing phenomena such as domain wall relaxation, spin wave-mediated instability regions and vortex-core mediated reversal dynamics. However, there has been no study on the direct observation of the switching process with the aid of a microwave signal input. We report a time-resolved imaging study of magnetization reversal in patterned magnetic structures under the influence of a field pulse with microwave assistance. The microwave frequency is varied to demonstrate the effect of resonant microwave-assisted switching. We observe that the swi…
Domain-Enhanced Interlayer Coupling in Ferroelectric/Paraelectric Superlattices
2004
We investigate the ferroelectric phase transition and domain formation in a periodic superlattice consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. We find that the polarization domains formed in the different FE layers can interact with each other via the PE layers. By coupling the electrostatic equations with those obtained by minimizing the Ginzburg-Landau functional we calculate the critical temperature of transition Tc as a function of the FE/PE superlattice wavelength and quantitatively explain the recent experimental observation of a thickness dependence of the ferroelectric transition temperature in KTaO3/KNbO3 strained-layer superlatti…
AC Switching of Relaxor PLZT Ceramics
2005
The switching under application of bipolar ac field is studied by recording of the hysteresis loops in wide temperature and field range in PLZT x/65/35 ceramics. The qualitative difference of the shape of hysteresis loops above and below the freezing temperature is attributed to backswitching in relaxor phase due to the depolarization field produced by the bound charges located at the interphase boundaries. The application of the quasistatic approach to analysis of the experimental data allows us to obtain parameters of the distribution function of local coercive fields from the field dependence of the switching charge derivative on field.
Continuous theory of switching in geometrically confined ferroelectrics
2014
A theory of ferroelectric switching in geometrically confined samples like thin films and multilayers with domain structure has been proposed. For that we use Landau–Khalatnikov (LK) equations with free energy functional being dependent on polarization gradients. In this case, the consistent theory can be developed as for thin ferroelectric films and multilayers the domain structure reduces to Fourier series in ferroelectric polarization. The specific calculations are presented for thin film ferroelectric with dead layers and ferro-/paraelectric multilayer. Our theory is generalizable to ferroelectrics and multiferroics with other geometries.
Spin-polarized Low Energy Electron Diffraction
2007
We review recent progress in the understanding of the physics of ultrathin ferromagnetic films and surfaces that has been made using elastic spin-polarized low-energy electron diffraction (SPLEED). Further development of the experimental technique including high efficient electron sources, spin manipulation and imaging allows a wide range of applications. We report on a quantitative comparison of relativistic dynamical scattering calculations with SPLEED experiments on Fe(110) surfaces and Fe(100)/W(100) thin films leading to an understanding of the spatial distribution of spin densities. Exploiting the surface sensitivity in combination with the large asymmetry of SPLEED, it becomes feasib…
Relation between deformation and polarization in the region of diffused phase transition of plzt 8/65/35
1995
Abstract The deformation as a function of polarization was measured in PLZT 8-10/65/35 in the region of diffused phase transition. A different behaviour of deformation in the region of double hysteresis loops was observed corresponding to ferroelectric and nonpolar phases as well as to the field induced phase transition region. In the ferroelectric phase the results are described by electrostriction. The decrease of volume as well as small longitudinal deformations at the field induced transition to ferroelectric state are explained by large remanent deformations, existing in the nonpolar phase. Since description of deformation in the framework of electrostriction cannot be motivated in the…