Alexander Melentev

The development of nanophotonics is hindered by a fundamental trade‐off between a material's refractive index ( n ) and its electronic bandgap ( E _g ), which severely restricts the choice of materials for short‐wavelength applications. This challenge is particularly acute in the visible and ultraviolet (UV) spectra, where high‐performance devices require materials that are simultaneously highly refractive and transparent. Here, we report on the van der Waals (vdW) crystal cadmium phosphorus trisulfide (CdPS ₃ ) as a solution to this long‐standing problem. Through comprehensive optical and structural characterization, we show that CdPS ₃ possesses an anomalously high in‐plane refractive index across the visible spectrum approaching three in the near‐UV, combined with a wide indirect bandgap. This combination of properties is validated by first‐principles calculations and direct near‐field imaging of highly confined waveguide modes. These findings establish CdPS ₃ as a leading material for UV–visible photonics, opening a new pathway for the development of high‐density integrated circuits and metasurfaces.

Divergent structures of laser-ablated defect-rich LiNbO ₃ and amorphous Nb ₂ O ₅ nanoparticles reveal defect engineering superior to amorphization for visible-light photocatalysts.

We recently demonstrated that the dielectric permittivity of a single-layer SrTiO3 thin film decreases with increasing thickness, and that incorporation of intermediate AlFeO3 layers into an SrTiO3 /AlFeO3 heterostructure mitigates this suppression of dielectric properties. We proposed two temperature-dependent mechanisms that could contribute to this effect: thermal strain and the formation of polar nanoregions (PNRs). In this study, we used Raman spectroscopy to assess the possibility of PNR formation in single-layer SrTiO3 films (50 and 250 nm thick) and in a multilayer heterostructure 5×[50 nm SrTiO3 + 50 nm AlFeO3. Our results show that the spectra of SrTiO3-containing structures exhibit telltale signs of PNR formation: the presence of symmetry-forbidden first-order modes and an asymmetric shape of the TO2 mode.

Modern optoelectronic devices demand materials that can perform multiple, often conflicting functions, such as acting as metals for interconnects, dielectrics for waveguides, and semiconductors for light emission and detection. The integration of these materials is challenging, slowing industry progress and increasing costs. It inspired an intensive search for an optoelectronic response within a single material. Here, we reveal that palladium diselenide (PdSe₂) provides an answer to this quest owing to its band structure. It exhibits a semimetallic band structure with a large bandgap for interband transitions responsible for semiconductor-metallic nature. This duality enables PdSe₂ to function as both a photodetector and a waveguide, integrating two traditionally incompatible responses. As a result, our findings provide a full picture of PdSe₂ optoelectronic properties, paving the way for its use in multifunctional optoelectronic applications.

THz spectroscopy reveals ferroelectric soft mode behavior in SrTiO₃/AlFeO₃ heterostructure compared to SrTiO₃ films. Intermediate AlFeO₃ layers prevent degradation of the intrinsic dielectric response of SrTiO₃ layers in the heterostructure.

Due to their high refractive index, record optical anisotropy and a set of excitonic transitions in visible range at a room temperature, transition metal dichalcogenides have gained much attention. Here, we adapted a femtosecond laser ablation for the synthesis of WSe₂ nanoparticles (NPs) with diameters from 5 to 150 nm, which conserve the crystalline structure of the original bulk crystal. This method was chosen due to its inherently substrate-additive-free nature and a high output level. The obtained nanoparticles absorb light stronger than the bulk crystal thanks to the local field enhancement, and they have a much higher photothermal conversion than conventional Si nanospheres. The highly mobile colloidal state of produced NPs makes them flexible for further application-dependent manipulations, which we demonstrated by creating substrates for SERS sensors.

Transition Metal Dichalcogenides (TMDCs) is a rich family of two-dimensional materials with outstanding electrical, mechanical and optical properties. Due to the high refractive index, record optical anisotropy, and a set of excitonic transitions in visible range at a room temperature, TMDCs gained much attention for resonant nanoantennas, subwavelength waveguides and all-dielectric metamaterials. To boost a further progress in the field of dielectric nanoresonators, a femtosecond laser ablation method is promising due to its inherently substrate-/additive-free nature and a high output level. We adapted this approach for the synthesis of WSe2 NPs of various size (from 5 to 150 nm), which conserve the crystalline structure of the bulk crystal. Obtained nanoresonators possess an enhanced optical absorption in comparison to the bulk crystal due to the effective volume field localization, and a photothermal conversion much stronger than that of conventional Si nanoscatters. A highly mobile colloidal state of produced NPs makes them flexible for further application-dependent manipulations.

Terahertz time-domain spectroscopy is used to perform the first detailed studies of the electrodynamic properties of MoRe (60%/40%) films with thicknesses ranging from 10 to 100 nm. Films are prepared by magnetron sputtering technique on silicon substrates. The critical temperatures vary from 6.5 K (for 10 nm film) to 9.5 K (for 100 nm film). Spectra of complex permittivity, conductivity, refraction index, surface impedance and reflection coefficient for the films are acquired at frequencies 0.15 - 2.4 THz (wavenumbers 5 – 80 cm^(-1)) and in the temperature interval T=5–300 K. For all films, temperature dependencies of the superconducting energy gap, penetration depth, superconducting condensate plasma frequency, and normalised superfluid density are obtained on a quantitative level. It is shown that the reduction of film thickness leads to a strong decrease of the critical temperature and magnitude of the energy gap. The observed suppression of superconductivity is assigned to reduction of the superconducting order parameter due to the contribution to the free energy of the electronic energy states at the surface of superconductor. The MoRe films with the obtained characteristics can be used in designing advanced superconducting electronic devices.