arXiv subjects

I. A. Eliseyev

Publications and source records attributed to I. A. Eliseyev.

10 recordsLinked to original sources

arXiv2026

Purcell enhancement in layered InSe on the Mie-resonant silicon nitride waveguide

Layered van der Waals semiconductors are promising active materials for nanoscale photonic and optoelectronic devices because their excitonic emission can be integrated with heterogeneous photonic architectures. For on-chip applications, this emission must be efficiently coupled to guided modes, while its recombination dynamics should be controlled by the local photonic environment. Although dielectric waveguides enable such integration, substantial control over radiative recombination generally requires resonant engineering of the local photonic density of states. Resonant dielectric nanostructures provide such control by modifying the photonic environment while preserving compatibility with guided-wave photonic architectures. Here, we demonstrate Purcell-enhanced excitonic emission from a thin InSe flake integrated with a Mie-resonant Si$_3$N$_4$ waveguide. The structure incorporates a resonant nanoparticle array with a resonance that overlaps the InSe PL band, thereby enhancing excitonic coupling to the guided mode. Optical spectroscopy confirms the designed resonance, while micro-photoluminescence measurements reveal enhanced and spectrally selective waveguide-coupled emission. Time-resolved photoluminescence measurements show a threefold shortening of the excitonic decay time relative to planar InSe. Analysis of the decay dynamics using a simple rate-equation model yields an effective Purcell factor of approximately 3 for the dominant out-of-plane excitonic emission channel. These results establish Mie-resonant dielectric waveguides as a compact platform for on-chip control of excitonic recombination in layered semiconductors.

cond-mat.mes-hall↗

arXiv2026

Role of magnon-magnon interaction in optical excitation of coherent two-magnon modes

Two-magnon modes are terahertz-frequency magnetic excitations in antiferromagnets, governed by exchange interactions, involving magnons from the entire Brillouin zone and dominated by zone-edge magnons. The ability to couple to light promotes two-magnon modes as contenders for ultrafast optical manipulation of the magnetic state, beyond conventional zone-center magnonics. While magnon-magnon interactions are known to critically shape the two-magnon line in spontaneous Raman scattering spectra, their role in coherent time-domain excitations remains unexplored. We report a detailed experimental and theoretical study of the influence of magnon-magnon interactions on coherent two-magnon modes in a cubic antiferromagnet excited via Impulsive Stimulated Raman scattering. We reveal the nontrivial evolution of coherent magnetic dynamics in the time domain and the corresponding spectrum and compare it with the spontaneous Raman scattering spectrum. By extending the spin-correlations based theory for two-magnon modes, we derive a unified description of their spectra in Raman Scattering and Impulsive Stimulated Raman Scattering and highlight the role of magnon-magnon interactions.

cond-mat.mtrl-sci↗

arXiv2025

Spin and lattice dynamics at the spin-reorientation transitions in the rare-earth orthoferrite Sm$_{0.55}$Tb$_{0.45}$FeO$_{3}$

Linear and non-linear couplings of magnetic and lattice excitations are at the heart of many fascinating magnetophononic phenomena observed in rare-earth orthoferrites, the distinctive feature of which is the tendency to spin-reorientation transitions. Here we report the results of the experimental study of the spin and lattice dynamics in the Brillouin zone center of the rare-earth orthoferrite Sm$_{0.55}$Tb$_{0.45}$FeO$_{3}$ by using polarized infrared reflectivity and Raman scattering spectroscopic techniques. The obtained results were supported by the first-principles calculations, which allowed us to reliably identify the parameters of most infrared- and Raman-active phonons. We reveal the spin-reorientation transitions $Γ_{4}(G_{a}F_{c}) \overset{T_{1}}\longleftrightarrow Γ_{24}(G_{ac}F_{ac}) \overset{T_{2}}\longleftrightarrow Γ_{2}(G_{c}F_{a})$ at $T_{1} \simeq 220$ K and $T_{2} \simeq 130$ K and carefully studied the following evolution of Raman scattering on magnetic excitations at these transitions. Notably, the intermediate magnetic structure $Γ_{24}$ displays an exceptionally broad temperature range $Δ{T} = T_{1} - T_{2} \simeq 90$ K in mixed Sm$_{0.55}$Tb$_{0.45}$FeO$_{3}$ compared to pure rare-earth orthoferrites. We attribute this broadening of the intermediate phase to the modification of the magnetocrystalline anisotropy as a result of the inhomogeneous magnetic structure caused by the random distribution of rare-earth $\mathrm{Sm}^{3+}$ and $\mathrm{Tb}^{3+}$ ions. We found neither change in the parameters of Raman-active $B_{1g}$ phonons nor the appearance of new phonons induced by spin-reorientation transitions, which have been reported in $\mathrm{SmFeO}_{3}$. We assume that our results provide a solid basis for more deeper understanding of magnetophononic phenomena in rare-earth orthoferrites.

cond-mat.mtrl-sci↗

arXiv2025

Photoluminescence Features of Few-Layer Hexagonal $α$-In$_2$Se$_3$

Indium (III) selenide is currently one of the most actively studied materials in the two-dimensional family due to its remarkable ferroelectric and optical properties. This study focuses on the luminescent properties of few-layer In$_2$Se$_3$ flakes with thicknesses ranging from 7 to 100 monolayers. To explore the photoluminescence features and correlate them with changes in crystal symmetry and surface potential, we employed a combination of techniques, including temperature-dependent micro-photoluminescence, time-resolved photoluminescence, Raman spectroscopy, atomic force microscopy, and Kelvin probe force microscopy. X-ray diffraction and Raman spectroscopy confirmed that the samples studied possess the $α$-polytype structure. The micro-photoluminescence spectrum consists of two bands, A and B, with band B almost completely disappearing at room temperature. Temperature-dependent photoluminescence and time-resolved measurements helped us to elucidate the nature of the observed bands. We find that peak A is associated with emission from interband transitions in In$_2$Se$_3$, while peak B is attributed to defect-related emission. Additionally, the photoluminescence decay times of In$_2$Se$_3$ flakes with varying thicknesses were determined. No significant changes were observed in the decay components as the thickness increased from 7 to 100 monolayers, suggesting that there are no qualitative changes in the band structure.

cond-mat.mtrl-sci↗

arXiv2024

Engineering whispering gallery modes in MoSe$_2$/WS$_2$ double heterostructure nanocavities: Towards developing all-TMDC light sources

Transition metal dichalcogenides (TMDCs) have emerged as highly promising materials for nanophotonics and optoelectronics due to their exceptionally high refractive indices, strong excitonic photoluminescence (PL) in monolayer configurations, and the versatility to engineer van der Waals (vdW) heterostructures. In this work, we exploit the intense excitonic PL of a MoSe$_2$ monolayer combined with the high refractive index of bulk WS$_2$ to fabricate microdisk cavities with tunable light emission characteristics. These microdisks are created from a 50-nm-thick WS$_2$/MoSe$_2$/WS$_2$ double heterostructure using frictional mechanical scanning probe lithography. The resulting cavities achieve a 4-10-fold enhancement in excitonic PL from the MoSe$_2$ monolayer at wavelengths near 800 nm. The excitonic PL peak is modulated by sharp spectral features, which correspond to whispering gallery modes (WGMs) supported by the cavity. A microdisk with a diameter of 2.35 $μ$m demonstrates WGMs with a quality factor of up to 700, significantly surpassing theoretical predictions and suggesting strong potential for lasing applications. The spectral positions of the WGMs can be finely tuned by adjusting the microdisk's diameter and thickness, as confirmed by theoretical calculations. This approach offers a novel route for developing ultra-compact, all-TMDC double heterostructure light sources with record-small size.

physics.optics↗

arXiv2024

Lattice dynamics and mixing of polar phonons in the rare-earth orthoferrite TbFeO$_{3}$

Rare-earth orthoferrites are a promising platform for antiferromagnetic spintronics with a rich variety of terahertz spin and lattice dynamics phenomena. For instance, it has been experimentally demonstrated that the light-driven optical phonons can coherently manipulate macroscopic magnetic states via nonlinear magnetophononic effects. Here using TbFeO$_{3}$ as an example, we reveal the origin of the mode mixing between the LO and TO phonons, which is important for understanding of nonlinear phononics. We performed a comprehensive study of the lattice dynamics of the TbFeO$_{3}$ single crystal by polarized infrared and Raman scattering spectroscopic techniques, and experimentally obtained and carefully analyzed the spectra of anisotropic complex dielectric functions in the far-infrared spectral range. This allowed us to reliably identify the symmetries and parameters of most infrared- and Raman-active phonons. Next, the experimental studies were supplemented by the lattice dynamics calculations which allowed us to propose the normal mode assignments. We reveal that the relation between LO and TO polar phonons is complex and does not strictly follow the ``LO-TO rule'' due to the strong mode mixing. We further analyze how displacements of different ions contribute to phonon modes and reveal that magnetic Fe ions are not involved in Raman-active phonons, thus shedding light on a lack of spin phonon coupling for such phonons. The obtained results establish a solid basis for further in-depth experimental research in the field of nonlinear phononics and magnetophononics in rare-earth orthoferrites.

cond-mat.mtrl-sci↗

arXiv2024

Strain in 2D TMDCs induced by metal-assisted exfoliation from the polyvinilalcohol-covered substrate

We have modified the metal-assisted transfer technique to obtain large-area few-layer flakes from transition metal dichalcogenides bulk crystals by introducing an initial stage - exfoliation of the bulk crystal onto an intermediate substrate, specifically a silicon wafer coated with polyvinyl alcohol. Following this, we thermally evaporate silver onto the sample and transfer the top layers of the crystal along with the silver layer to the target substrate. This technique allows the production of visually non-corrugated single- and few-layer flakes with high yield. A direct comparison of the micro-Raman and micro-photoluminescence spectra of flakes exfoliated using our method with the spectra of those exfoliated from scotch tape reveals differences in their properties. We identify signatures of deformations in the flakes exfoliated from the intermediate substrate, indicating the presence of static friction between the substrate and the flake. Our findings thus suggest a novel method to induce intrinsic deformation in 2D materials.

cond-mat.mtrl-sci↗

arXiv2024

Laser-induced Demagnetization in van der Waals $XY$- and Ising-like Antiferromagnets NiPS$_3$ and FePS$_3$

The critical behaviour of laser-induced changes in magnetic ordering is studied experimentally in two-dimensional zigzag antiferromagnets $XY$-like NiPS$_3$ and Ising-like FePS$_3$. To examine laser-induced dynamics in flakes of these compounds, we employ time-resolved exchange linear dichroism effect sensitive to zigzag magnetic ordering and independent of the orientation of the antiferromagnetic vector. In both compounds laser excitation in the vicinity of the absorption edge induces partial quenching of the antiferromagnetic ordering manifested by exchange linear dichroism reduction. The amplitude of the effect varies with temperature as the derivative of the antiferromagnetic vector and exhibits a critical behaviour with the exponents corresponding to $XY$- and Ising-models for NiPS$_3$ and FePS$_3$, respectively. Critical slowing down of the demagnetization in the vicinity of Néel temperature is found, however, only in FePS$_3$. In contrast, the increase of the demagnetization time near the ordering temperature in NiPS$_3$ is minor. We show that the difference in the demagnetization times correlates well with the spin specific heat in both compounds. Beyond the range of slowing down, the demagnetization times in NiPS$_3$ and FePS$_3$ are comparable, about 5 - 10 ps, and are longer than those reported earlier for CoPS$_3$ and considerably shorter than for MnPS$_3$. This points to the importance of the unquenched angular momentum of transition-metal ions in laser-induced demagnetization process.

cond-mat.mes-hall↗

arXiv2024

Direct observation of split-mode exciton-polaritons in a single MoS$_2$ nanotube

A single nanotube synthesized from a transition metal dichalcogenide (TMDC) exhibits strong exciton resonances and, in addition, can support optical whispering gallery modes. This combination is promising for observing exciton-polaritons without an external cavity. However, traditional energy-momentum-resolved detection methods are unsuitable for this tiny object. Instead, we propose to use split optical modes in a twisted nanotube with the flattened cross-section, where a gradually decreasing gap between the opposite walls leads to a change in mode energy, similar to the effect of the barrier width on the eigenenergies in the double-well potential. Using micro-reflectance spectroscopy, we investigated the rich pattern of polariton branches in single MoS$_2$ tubes with both variable and constant gaps. Observed Rabi splitting in the 40 - 60 meV range is comparable to that for a MoS$_2$ monolayer in a microcavity. Our results, based on the polariton dispersion measurements and polariton dynamics analysis, present a single TMDC nanotube as a perfect polaritonic structure for nanophotonics.

cond-mat.mes-hall↗

arXiv2020

State-of-the-art and prospects for intense red radiation from core-shell InGaN/GaN nanorods

Core-shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) are promising for monolithic white light-emitting diodes and multicolor displays. Such applications, however, are still a challenge because intensity of red band is too weak as compared with blue and green ones. To clarify the problem, we have performed power and temperature dependent, as well as time-resolved measurements of photoluminescence (PL) in NRs of different In content and diameter. These studies have shown that the dominant PL bands originate from nonpolar and semipolar QWs, while a broad yellow-red band arises mostly from defects in the GaN core. Intensity of red emission from the polar QWs at the NR tip is fatally small. Our calculation of electromagnetic field distribution inside the NRs shows a low density of photon states in the tip that suppresses the red radiation. We suggest a design of hybrid NRs, in which polar QWs, located inside the GaN core, are pumped by UV-blue radiation of nonpolar QWs. Possibilities of radiative recombination rate enhancement by means of the Purcell effect are discussed.

cond-mat.mtrl-sci↗