Condensed Matter

11 pages, 962 KiB

Open AccessArticle

Possible Realization of Hyperbolic Plasmons in Few-Layered Rhenium Disulfide

by Ravi Kiran, Dimitar Pashov, Mark van Schilfgaarde, Mikhail I. Katsnelson, Arghya Taraphder and Swagata Acharya

Condens. Matter 2025, 10(3), 40; https://doi.org/10.3390/condmat10030040 - 19 Jul 2025

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Abstract

Hyperbolic plasmons are a highly desired property in optoelectronics and biomolecular sensing. The necessary condition to realize hyperbolic plasmons is a significant anisotropy of the principal components of the dielectric function, such that at a certain frequency range, one component is negative and [...] Read more.

{ReS}_{2}

, and our theory shows that

{ReS}_{2}

can host hyperbolic plasmons in the ultraviolet frequency range. The operating frequency range of the hyperbolic plasmons can be tuned with the number of

{ReS}_{2}

layers. However, we note that the significantly large imaginary part of the macroscopic dielectric response in all layered variants of ReS₂ can result in substantial losses for the hyperbolic plasmons, as in the case with other known hyperbolic materials, with the exception of MoOCl₂. We also note that ReS₂ hosts ultraviolet hyperbolic plasmons while ZrSiSe, WTe₂, and CuS nanocrystals host infrared plasmons, providing a novel platform for optoelectronics in the ultraviolet range. Full article

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16 pages, 1799 KiB

Open AccessArticle

Skyrmion Crystal in Bilinear–Biquadratic–Bicubic Model on a Centrosymmetric Triangular Lattice

by Satoru Hayami

Condens. Matter 2025, 10(3), 39; https://doi.org/10.3390/condmat10030039 - 18 Jul 2025

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Abstract

We numerically investigate the effect of multi-spin interactions on the stability of skyrmion crystals and other multiple-Q magnetic states, with a particular emphasis on the momentum-resolved bicubic interaction. By performing simulated annealing for an effective spin model that incorporates bilinear, biquadratic, and bicubic interactions on a two-dimensional triangular lattice, we construct the corresponding low-temperature phase diagram. Our results reveal that a positive bicubic interaction stabilizes a skyrmion crystal with a skyrmion number of two, whereas a negative bicubic interaction favors a single-Q spiral state. Moreover, we demonstrate that the stability region of the field-induced skyrmion crystal with the skyrmion number of one is largely enlarged in the presence of a positive bicubic interaction. Full article

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24 pages, 7332 KiB

Open AccessArticle

High-Performance Natural Dye-Sensitized Solar Cells Employing a New Semiconductor: Gd₂Ru₂O₇ Pyrochlore Oxide

by Assohoun F. Kraidy, Abé S. Yapi, Joseph K. Datte, Michel Voue, Mimoun El Marssi, Anthony Ferri and Yaovi Gagou

Condens. Matter 2025, 10(3), 38; https://doi.org/10.3390/condmat10030038 - 14 Jul 2025

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Abstract

We investigated a novel natural dye-sensitized solar cell (DSSC) utilizing gadolinium ruthenate pyrochlore oxide Gd₂Ru₂O₇ (GRO) as a photoanode and compared its performance to the TiO₂-Gd₂Ru₂O₇ (TGRO) combined-layer configuration. The films were fabricated using the spin-coating technique, resulting in spherical grains with an estimated mean diameter of 0.2 µm, as observed via scanning electron microscopy (SEM). This innovative photoactive gadolinium ruthenate pyrochlore oxide demonstrated strong absorption in the visible range and excellent dye adhesion after just one hour of exposure to natural dye. X-ray diffraction confirmed the presence of the pyrochlore phase, where Raman spectroscopy identified various vibration modes characteristic of the pyrochlore structure. Incorporating Gd₂Ru₂O₇ as the photoanode significantly enhanced the overall efficiency of the DSSCs. The device configuration FTO/compact-layer/Gd₂Ru₂O₇/Hibiscus-sabdariffa/electrolyte(I⁻/I₃⁻)/Pt achieved a high efficiency of 9.65%, an open-circuit voltage (Voc) of approximately 3.82 V, and a current density of 4.35 mA/cm² for an active surface area of 0.38 cm². A mesoporous TiO₂-based DSSC was fabricated under the same conditions for comparison. Using impedance spectroscopy and cyclic voltammetry measurements, we provided evidence of the mechanism of conductivity and the charge carrier’s contribution or defect contributions in the DSSC cells to explain the obtained Voc value. Through cyclic voltammetry measurements, we highlight the redox activities of hibiscus dye and electrolyte (I⁻/I₃⁻), which confirmed electrochemical processes in addition to a photovoltaic response. The high and unusual obtained Voc value was also attributed to the presence in the photoanode of active dipoles, the layer thickness, dye concentration, and the nature of the electrolyte. Full article

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5 pages, 197 KiB

Open AccessCommunication

Nevanlinna Analytical Continuation of the Central Charge in 2D Conformal Field Theory

by Bernardo Barbiellini

Condens. Matter 2025, 10(3), 37; https://doi.org/10.3390/condmat10030037 - 8 Jul 2025

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Abstract

We present an analytic continuation of the central charge c in two-dimensional conformal field theory (2D CFT), modeled as a Nevanlinna function—an analytic map from the upper half-plane to itself. Motivated by the structure of vacuum energies arising from the quantization of spin- [...] Read more.

c (j) = 1 + 6 j (j + 1)

and extend it continuously via

c (z) = 1 + 6 z

. The Möbius-inverted form

f (z) = 1 - 6 / z

satisfies the conditions of a Nevanlinna function, providing a physically consistent analytic structure that captures both the unitarity of minimal models (

c < 1

) and the continuous spectrum for

c \geq 1

. This unified framework highlights the connection between spectral theory, analyticity, and conformal symmetry in quantum field theory. Full article

(This article belongs to the Special Issue The Universe Observed With Particle Detectors: Celebrating the Scientific Legacy of Prof. Guido Barbiellini Amidei)

18 pages, 1546 KiB

Open AccessArticle

Ultrasound-Assisted Synthesis for the Control of Silver Nanoparticle Size: A Preliminary Study on the Influence of Pressure and pH

by Paula Riascos, Daniel Llamosa, Jahaziel Amaya and Hansen Murcia

Condens. Matter 2025, 10(3), 36; https://doi.org/10.3390/condmat10030036 - 7 Jul 2025

Viewed by 426

Abstract

The use of plasmonic nanoparticles for biosensor technology is dependent on nanoparticle size and morphology. This study determined the effect of pH and pressure on synthesizing silver nanoparticle size. In Method 1, a mixture of NaBH₄ and sodium citrate was added to a solution of AgNO₃ monodispersed by ultrasound energy. In Method 2, the reducer was added to the precursor–dispersant mixture solution. The effect of pH was evaluated by using buffer solutions at pH 4.0, pH 7.0, and pH 10.0 and water as control. To determine the effect of pressure, AgNPs were subjected to 0, 4, and 23 h to 1.75 MPa at 200 °C. AgNPs produced with Method 1 showed a more symmetric SPR and a smaller nanoparticle diameter (±6 nm). The SPR with Method 1 at pH 10.0 produced a higher UV peak with a shift around 20 nm. In the case of the pressure treatment, a shift of approximately 20 nm was observed at all time conditions studied, and a higher AgNP diameter was found in contrast to Method 1. Finally, EDX and Raman analysis confirm the presence of AgNPs and a mild oxidation of these. These results suggest that alkalinity and pressure can affect the diameter of AgNPs. Full article

(This article belongs to the Section Physics of Materials)

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Condens. Matter, Volume 10, Issue 3 (September 2025) – 5 articles

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