S. Schwieger

Green function theory versus quantum Monte Carlo calculations for thin magnetic films

In this work we compare numerically exact quantum Monte Carlo (QMC) calculations and Green function theory (GFT) calculations of thin ferromagnetic films including second-order anisotropies. Thereby, we concentrate on easy-plane systems, i.e., systems for which the anisotropy favors a magnetization parallel to the film plane. We discuss these systems in perpendicular external field, i.e.,

CALCULATION AND INTERPRETATION OF SURFACE-PLASMON-POLARITON FEATURES IN THE REFLECTIVITY OF METALLIC NANOWIRE ARRAYS

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Surface plasmon polariton – exciton interaction in metal-semiconductor and metal-dye nanostructures

parallel to the film normal. GFT results are in good agreement with QMC for high enough fields and temperatures. Below a critical field or a critical temperature, no collinear stable magnetization exists in GFT. On the other hand, QMC gives finite magnetization even below those critical values. This indicates that there occurs a transition from noncollinear to collinear configurations with increasing field or temperature. For slightly tilted external fields, a rotation of magnetization from out-of-plane to in-plane orientation is found with decreasing temperature.

Surface plasmon polaritons on arrays of nanostructures with three‐fold symmetry

The far-field reflectivity of metallic nanowire arrays designed to show strong surface-plasmon-polariton (SPP) resonances is studied numerically. The results of calculations in time and frequency space as well as the results of semi-analytic theories using different approximative boundary conditions at the metal surfaces are evaluated and compared. Good agreement between all different methods is obtained in most cases. The SPP-related features are superimposed on a strongly varying background. Combining FDTD simulations, finite element results, and semi-analytical calculations, the microscopic origin of the background contribution is identified. Resonant transmission through sub-wavelength slits leads to pronounced oscillations in the far-field reflectivity as a function of the height of the nanowires.

Tunable nanowires : An additional degree of freedom in plasmonics

We consider the frequency- and angle-dependent reflectivity of hybrid structures containing metallic components and an optically excitable medium such as organic dyes or semiconductor quantum wells. Clear signatures of a coupling between surface plasmon polaritons and excitons in the excitable medium, in particular avoided crossings with hybridization gaps in the range ≈ 10–100 meV, are found both experimentally and theoretically.

The influence of wire shape on surface plasmon mode distribution

The influence of nano‐holes with three‐fold symmetry on the excitation of surface plasmon polaritons (SPPs) at metallic nano‐hole arrays is studied numerically for a quadratic array of rotor‐shaped nano‐holes cut into a silver film. It is found that the SPP‐related minimum of the far‐field reflectivity shifts as a function of the polarization angle of the incident light compared to rotational invariant hole‐shapes. This was also reported in recent experiments. On contrast, the polarization angle for most efficient SPP‐excitation is found to be independent of the nano‐hole shape. We discuss optical near‐ and far‐field properties of the considered structures.