The method of simple iterations with correction of convergence and the minimal discrepancy method for plasmonic problems

The problem of searching for complex roots of the dispersion equations of plasmon-polaritons along the boundaries of the layered structure-vacuum interface is considered. Such problems arise when determining proper waves along the interface of structures supporting surface and leakage waves, including plasmons and polaritons along metal, dielectric and other surfaces. For the numerical solution of the problem, we consider a modification of the method of simple iterations with a variable iteration parameter leading to a zero derivative of the right side of the equation at each step, i.e. convergent iterations, as well as a modification of the minimum residuals method. It is shown that the method of minimal residuals with linearization coincides with the method of simple iterations with the specified correction. Convergent methods of higher orders are considered. The results are demonstrated by examples, including complex solutions of dispersion equations for plasmon-polaritons. The advantage of the method over other methods of searching for complex roots in electrodynamics problems is the possibility of ordering the roots and constructing dispersion branches without discontinuities. This allows you to classify modes.

Surface waves on the inhomogeneous interface between radiative electron–ion plasma and vacuum

The impact of temperature inhomogeneity, surface charge and surface mass densities on the stability analysis of charged surface waves at the interface between dense, incompressible, radiative, self-gravitating magnetized electron–ion plasma and vacuum is investigated. For such an incompressible plasma system, the temperature inhomogeneity is governed by an energy balance equation. Adopting the one-fluid magnetohydrodynamic (MHD) approximation, a general dispersion relation is obtained for capillary surface waves, which takes into account gravitational, radiative and magnetic field effects. The dispersion relation is analysed to obtain the conditions under which the plasma–vacuum interface may become unstable. In the absence of electromagnetic (EM) pressure, astrophysical objects undergo gravitational collapse through Jeans surface oscillations in contrast to the usual central contraction of massive objects due to enhanced gravity. EM radiation does not affect the dispersion relation much, but actually tends to stabilize the Jeans surface instability. In certain particular cases, pure gravitational radiation may propagate on the plasma vacuum interface. The growth rate of radiative dissipative instability is obtained in terms of the wavevector. Our theoretical model of the Jeans surface instability is applicable in astrophysical environments and also in laboratory plasmas.

Potential Dependence of the Ionic Structure at the Ionic Liquid/water Interface Studied Using MD Simulation

<div> <p>The structure at the electrochemical liquid/liquid interface between water (W) and trioctylmethylammonium bis (nonafluorobutanesulfonyl)amide, a hydrophobic ionic liquid (IL), was studied using molecular dynamics (MD) simulation in which the interfacial potential difference was controlled. On the IL side of the IL|W interface, ionic multilayers were found in the number density distribution of IL ions whereas monolayer-thick charge accumulation was found in the charge density distribution. This suggests that the potential screening is completed within the first ionic layer and the effect of overlayers on the potential is marginal. The W side of the interface showed the diffuse electric double layer as expected, and also unveiled a density depletion layer, indicating that the IL surface is hydrophobic enough to be repelled by water. The IL ions in the first ionic layer showed anisotropic orientation even at the potential of zero charge, in which the polar moieties were oriented to the W side and the non-polar moieties preferred parallel to the interface. When an electric field is applied across the interface so that the IL ions are more accumulated, the non-polar moieties changed the parallel preference to more oriented to the IL side due to the dipolar nature of the IL ions. The ionic orientations at the IL|W interface were compared with those at other two IL interfaces, the vacuum and graphene interfaces of the IL. The parallel preference of the non-polar moieties was similar at the IL|graphene interface but different from the perpendicular orientation toward the vacuum side at the IL|vacuum interface. The comparison suggests that water behaves like a wall repelling IL ions like a solid electrode.</p></div>

Potential Dependence of the Ionic Structure at the Ionic Liquid/water Interface Studied Using MD Simulation

<div> <p>The structure at the electrochemical liquid/liquid interface between water (W) and trioctylmethylammonium bis (nonafluorobutanesulfonyl)amide, a hydrophobic ionic liquid (IL), was studied using molecular dynamics (MD) simulation in which the interfacial potential difference was controlled. On the IL side of the IL|W interface, ionic multilayers were found in the number density distribution of IL ions whereas monolayer-thick charge accumulation was found in the charge density distribution. This suggests that the potential screening is completed within the first ionic layer and the effect of overlayers on the potential is marginal. The W side of the interface showed the diffuse electric double layer as expected, and also unveiled a density depletion layer, indicating that the IL surface is hydrophobic enough to be repelled by water. The IL ions in the first ionic layer showed anisotropic orientation even at the potential of zero charge, in which the polar moieties were oriented to the W side and the non-polar moieties preferred parallel to the interface. When an electric field is applied across the interface so that the IL ions are more accumulated, the non-polar moieties changed the parallel preference to more oriented to the IL side due to the dipolar nature of the IL ions. The ionic orientations at the IL|W interface were compared with those at other two IL interfaces, the vacuum and graphene interfaces of the IL. The parallel preference of the non-polar moieties was similar at the IL|graphene interface but different from the perpendicular orientation toward the vacuum side at the IL|vacuum interface. The comparison suggests that water behaves like a wall repelling IL ions like a solid electrode.</p></div>

Robust magnetic anisotropy of a monolayer of hexacoordinate Fe(ii) complexes assembled on Cu(111)

The tris pyrazolyl borate ligand imposes a rigid scaffold around Fe(ii) ensuring a robust magnetic anisotropy when the molecules assembled as monolayers suffer from the dissymmetric environment of the substrate/vacuum interface.

Probing embedded topological modes in bulk-like GeTe-Sb2Te3 heterostructures

The interface between topological and normal insulators hosts metallic states that appear due to the change in band topology. While topological states at a surface, i.e., a topological insulator-air/vacuum interface, have been studied intensely, topological states at a solid-solid interface have been less explored. Here we combine experiment and theory to study such embedded topological states (ETSs) in heterostructures of GeTe (normal insulator) and $$\hbox {Sb}_2$$ Sb 2 $$\hbox {Te}_3$$ Te 3 (topological insulator). We analyse their dependence on the interface and their confinement characteristics. First, to characterise the heterostructures, we evaluate the GeTe-Sb$$_2$$ 2 Te$$_3$$ 3 band offset using X-ray photoemission spectroscopy, and chart the elemental composition using atom probe tomography. We then use first-principles to independently calculate the band offset and also parametrise the band structure within a four-band continuum model. Our analysis reveals, strikingly, that under realistic conditions, the interfacial topological modes are delocalised over many lattice spacings. In addition, the first-principles calculations indicate that the ETSs are relatively robust to disorder and this may have practical ramifications. Our study provides insights into how to manipulate topological modes in heterostructures and also provides a basis for recent experimental findings [Nguyen et al. Sci. Rep. 6, 27716 (2016)] where ETSs were seen to couple over thick layers.