Abstract
Photoexcitation and shaping of a propagating surface plasmon polariton (SPP) on silver and gold microstructures are well established and lead to the discovery of the plasmonic spin-Hall effect recently. Whereas silver is often the material of choice due to its exceptional low plasma frequency and weak damping, similar observations have not been reported for ferromagnetic metals. In this work, we report on propagating SPPs on Ni80Fe20 microstructures imaged by photoemission electron microscopy (PEEM) in combination with a tunable femtosecond laser system at MHz repetition rate. Circular dichroic (CD) images in threshold PEEM show clear edge-induced SPPs with sub-micrometer wavelength and propagation length of about 3.5 μm. Analysis of the interference patterns as well as the coupling of the optical spin angular momentum to the observed fringe fields reveal propagation characteristics exclusive to evanescent waves and the presence of the plasmonic spin-Hall effect. Our work provides direct evidence that many materials with a high plasma frequency allow for excitation and observation of propagating SPPs at the dielectric/metal interface via CD PEEM imaging, enabling magnetoplasmonic investigation of common ferromagnets on nanometer length and femtosecond time scales.
Highlights
Due to the remarkable progress in nanofabrication on the one hand and magneto optical methods on the other, the vivid field of magnetoplasmonics has become more and more accessible by a variety of excitation and observation techniques [1, 2]
We report on propagating surface plasmon polariton (SPP) on Ni80Fe20 microstructures imaged by photoemission electron microscopy (PEEM) in combination with a tunable femtosecond laser system at MHz repetition rate
Our work provides direct evidence that many materials with a high plasma frequency allow for excitation and observation of propagating SPPs at the dielectric/metal interface via Circular dichroic (CD) PEEM imaging, enabling magnetoplasmonic investigation of common ferromagnets on nanometer length and femtosecond time scales
Summary
Due to the remarkable progress in nanofabrication on the one hand and magneto optical methods on the other, the vivid field of magnetoplasmonics has become more and more accessible by a variety of excitation and observation techniques [1, 2]. Another approach coherently launches SPPs with the aid of an array referred to as magnetoplasmonic crystal, resulting in a plasmonic standing wave pattern and a resonant enhancement of the magneto-optical activity [20, 21] Following this approach in photoemission electron microscopy (PEEM) experiments [21], SPPs at magnetic microstructures were imaged directly with nanometer spatial resolution using variable incident light polarization and photon energy. It has been recently discovered that the evanescent electric field creates an additional spin angular momentum (SAM) perpendicular to the propagation direction of the SPP [26, 27, 28] This additional SAM allows for selective excitation of SPPs at different edges of a microstructure as shown in figure 1 [29, 30], and can be related to the plasmonic spin-Hall effect [31]. We facilitate this observation to identify propagating SPPs on Ni80Fe20 for the first time and extract their wavelength and propagation length, providing valuable insights into the dielectric properties at the surface
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