arXiv subjects

Javier Yeste

Publications and source records attributed to Javier Yeste.

3 recordsLinked to original sources

arXiv2026

Cd(Zn)O on SiC: epsilon-near-zero modes and plasmon-phonon coupling

Cd(Zn)O stands out as probably the best plasmonic material in the mid-IR, but it is usually grown on sapphire or other passive substrates. In this work we introduce SiC as a novel, highly polar, dopable substrate for Cd(Zn)O. The Cd(Zn)O/SiC system is analyzed as a function of the Zn concentration and thin film thickness, and the results are compared to those obtained in the Cd(Zn)O/sapphire system. XRD and reflectance measurements show that the alloy with 10 % Zn nominal concentration has the best crystalline and plasmonic quality, with optical losses as good as 13 % of the plasma frequency. The thin films show two surface polariton modes: a purely plasmonic symmetric mode at higher energies with negligible frequency dispersion and pinning at the plasma frequency for the thinnest films, characteristic of an ideal epsilon-near-zero mode; and a plasmonic-phononic hybridized antisymmetric mode at lower energies, which thanks to the large value of the higher frequency dielectric constant of SiC compared to sapphire, shows much lower frequency dispersion, indicative of the stronger epsilon-near-zero character. Hence, Cd(Zn)O/SiC offers a promising platform for the development of ENZ devices on an active substrate.

physics.optics↗

arXiv2025

Near Field Enhancement via Plasmon Phonon Polariton Coupling with CdO Stripes

The mid-infrared spectral region presents significant potential for sensing and spectroscopic applications. However, traditional plasmonic materials exhibit substantial optical losses within this range, thereby constraining their effectiveness. Emerging materials such as cadmium oxide (CdO) have demonstrated promise in overcoming these limitations. In this work, we introduce a novel approach to engineer large coupling between localized surface plasmons (LSPs) in CdO and localized surface phonon polaritons (LSPhP) in sapphire. By developing a successful dry etching protocol for CdO, we fabricate stripe arrays with tunable sizes, allowing the spectral alignment between the LSP and LSPhP modes. We demonstrate both experimentally and numerically that when these polaritons become resonant, hybrid modes emerge, resulting in coupling. Finite element simulations reveal near-field enhancements exceeding a factor of 1000, spatially extended hundreds of nanometers around the etched structures. Our approach bridges the plasmonic and phononic responses of two mid-IR active materials, paving the way for scalable, high-performance infrared sensing platforms.

physics.optics↗

arXiv2021

Direct imaging of chiral domain walls and Néel-type skyrmionium in ferrimagnetic alloys

The evolution of chiral spin structures is studied in ferrimagnet Ta/Ir/Fe/GdFeCo/Pt multilayers as a function of temperature using scanning electron microscopy with polarization analysis (SEMPA). The GdFeCo ferrimagnet exhibits pure right-hand Néel-type domain wall (DW) spin textures over a large temperature range. This indicates the presence of a negative Dzyaloshinskii-Moriya interaction (DMI) that can originate from both the top Fe/Pt and the Co/Pt interfaces. From measurements of the DW width, as well as complementary magnetic characterization, the exchange stiffness as a function of temperature is ascertained. The exchange stiffness is surprisingly mostly constant, which is explained by theoretical predictions. Beyond single skyrmions, we find by direct imaging a pure Néel-type skyrmionium, which due to the absence of a skyrmion Hall angle is a promising topological spin structure to enable high impact potential applications in the next generation of spintronic devices.

cond-mat.mtrl-sci↗