Multi-frequency surface plasmons supported with a nanoscale non-uniform 2D electron gas formed due to a polar catastrophe at the oxide interface, dispersions, diffractions, and beyond

Tuning d-Orbital Electronic Structure via Au-Intercalated Two-Dimensional Fe3GeTe2 to Increase Surface Plasmon Activity

While extensive research has been dedicated to plasmon tuning within non-noble metals, prior investigations primarily concentrated on markedly augmenting the inherently low concentration of free carriers in materials with minimal consideration given to the influence of electron orbitals on surface plasmons. Here, we achieve successful intercalation of Au atoms into the layered structure of Fe3GeTe2 (FGT), thereby exerting control over the orbital electronic states or structure of FGT. This intervention not only amplifies the charge density and electron mobility but also mitigates the loss associated with interband transitions, resulting in increased two-dimensional FGT surface plasmon activity. As a consequence, Au-intercalated FGT detects crystal violet molecules as a surface-enhanced Raman scattering substrate, and the detection lines are 3 orders of magnitude higher than before Au intercalation. Our work provides insight for further studies on plasmon effects and the relation between surface plasmon resonance behavior and electronic structures.

Surface plasmon induced spot and line formation at interfaces of ITO coated LiNbO3 slabs and gigantic nonlinearity

Remarkable spots and lines were clearly observed at the two interfaces of indium-tin-oxide coated Z-cut Fe-doped lithium noibate plates under illumination by milliwatt continuous-wave laser light; this occurred because of the visible surface plasmons (SPs) supported by the promising non-metal plasmonic system. The intriguing observations are here explained via the SP-strengthened nonlinear effect, through consideration of the electrostatic field (which is comparable to the atomic field) and its large gradient; this hints at a promising, highly sensitive plasmonic system. The gigantic nonlinear effect discussed in this paper should be ubiquitously existed in many oxide ferroelectric/semiconductor combinations and is promising for visible plasmonic applications.

The CdTiO3/BaTiO3 superlattice interface from first principles

The oxide interface has been studied extensively in the past decades and exhibits different physical properties from the constituent bulks. Using first-principles electronic structure calculations, we investigated the interface of CdTiO₃/BaTiO₃ (CTO/BTO) superlattice with ferroelectric BaTiO₃. In this case, the conduction bands of CdTiO₃ are composed of Cd-5s orbitals with low electron effective mass and nondegenerate dispersion, and thus expected to have high mobility. We predicted a controllable conductivity at the interface, and further analyzed how the polarization direction and strength affect the conductivity. We also explored the relationship between two components: thickness and polarization. Intriguingly, the total polarization in CTO/BTO might be even larger than that of ferroelectric bulk BaTiO₃. Therefore, we found a way to maximize the superlattice polarization by increasing the fraction of the CdTiO₃ layers, based on the interesting dependence of the total polarization and CTO/BTO ratio.

Young's double-slit-like diffraction stemming from scattering of long-ranged surface plasmon polaritons along distinct ±Z-faces' metallic layers in indium-tin-oxide coated Fe doped LiNbO3

Young's double-slit-like diffraction was seen on a viewing screen placed perpendicularly to a sharply cut edge of a Z-cut iron doped LiNbO₃ (LN) slab coated with indium-tin-oxide (ITO) films. The high contrast fringes observed confirm two sets of visible long-ranged surface plasmon polaritons propagating along the two ITO-LN interfaces distinctly over 5 mm path length with well-kept coherency, apart from metal uses. The indices of refraction measured with polarimetry from the ±Z-faces and changing transmission spectra obtained are consistent with the physical picture, along with dynamics of the very first reflection from the -Z-face under varying polarization angles between the two incident laser beams onto the slab.

Charge accumulation resulting in metallization of II-VI semiconductor (ZnX X = O, S, Se) films neighboring polar liquid crystal molecules and their surface plasmonic response in the visible region

The surfaces of some IIB-VI semiconductors (ZnX, X = O, S, Se) are metallized by neighboring highly polar and atomically vertically aligned (VA) liquid crystal (LC) molecules. Owing to polar catastrophe, the charge carriers swarm in an extremely thin layer and the density can achieve 4.86 × 1028 m-3 close to the LC layer, which can be regarded as a 2-dimensional electron gas (2DEG). Using density functional theory (DFT), it was found that the dielectric functions of the modified layer become negative in the visible region. This indicates the semiconductor/LC platform is an ideal active plasmonic candidate, apart from the lossy metal constituents. Experimentally, after mediation with phase gratings written in the LC system, surface plasmon polaritons (SPPs) can be excited at the semiconductor surface and localized charges are gathered in an adjacent LC layer. With the help of the enhanced static electric field from the metallic surface, significantly more 2D diffraction orders in many rows and columns and a huge energy transfer between the laser beams and SPPs was observed, which is consistent with the metallization results and the bidirectional coupling between the SPPs and incident lights. The generalization of the II-VI semiconductors means the system has great promise for use in practical applications owing to the ultra-low loss. The novel insights regarding this combination with liquid crystals will be beneficial for real-time holographic displays and the study of tunable epsilon near zero points.

Asymmetrical 1st reflection trend owing to metallization difference at ± Z-faces in indium tin oxide coated Fe-doped lithium niobate

The charges accumulated at the interface of indium tin oxide (ITO) and iron doped lithium niobate (LN) in an extremely thin layer because of semiconductor band alignment were analyzed with ab initio theory. The formation of 2D electron gas makes the interface metallic and the excitation of surface plasmon polaritons (SPPs) possible. In experiments, diametrically opposite trends of the very first reflection (VFR) on the ± Z-faces of ITO coated Fe-LN slabs were observed and associated with the differences in metallization and the photovoltaic charge accumulation there. Microscopically, the electric environments of the two ITO/LN interfaces differ greatly owing to spontaneous polarization and photovoltaic fields, which alter the band structures and band alignment, resulting in phase gratings with a π-shift difference recorded at the two interfaces. This affects the opposite energy coupling between the SPPs and laser beams and results in the dramatically opposite trends of VFR.