Condensed Matter

12 pages, 1987 KB

Open AccessArticle

The Superconducting Properties of Elemental Pb Under Pressure

by Shu-Ke Xuan, Yuan-Fang Yue, Xiao-Ming Li and Xun-Wang Yan

Condens. Matter 2025, 10(3), 49; https://doi.org/10.3390/condmat10030049 - 12 Sep 2025

Based on first-principles calculations, we systematically investigate the crystal structure, electronic structure, and superconductivity of metallic lead under pressure. The results show that with the increase of pressure, the crystal structure of lead evolves from face-centered cubic (fcc) to hexagonal close-packed (hcp) and [...] Read more.

Based on first-principles calculations, we systematically investigate the crystal structure, electronic structure, and superconductivity of metallic lead under pressure. The results show that with the increase of pressure, the crystal structure of lead evolves from face-centered cubic (fcc) to hexagonal close-packed (hcp) and then to body-centered cubic (bcc). In different crystal structure phases, the variation laws of electronic structure and superconducting properties with pressure are studied. It is found that the superconducting transition temperature decreases with the increase of pressure in fcc, hcp, and bcc phases. The physical mechanism for this change is explained. The calculation results indicate that elemental metallic lead remains metallic with the increase of pressure, but the electron density of states at the Fermi level decreases, leading to the decrease of the electron-phonon coupling constant (

λ

) and superconducting transition temperature (

T_{c}

) from 7.1 K to 0.04 K. In addition, with the increase of pressure, there is no phenomenon of s electrons transforming into d electrons, which is different from the superconducting behavior of zirconium metal under pressure. These studies explain the superconductivity of elemental metallic lead under high pressure and provide theoretical support for the experiments and applications of lead-based superconductors. Full article

(This article belongs to the Section Superconductivity)

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20 pages, 3263 KB

Open AccessArticle

The Response of a Linear, Homogeneous and Isotropic Dielectric and Magnetic Sphere Subjected to an External Field, DC or Low-Frequency AC, of Any Form

by Dimosthenis Stamopoulos

Condens. Matter 2025, 10(3), 48; https://doi.org/10.3390/condmat10030048 - 1 Sep 2025

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Abstract

Maxwell’s equations epitomize our knowledge of standard electromagnetic theory in vacuums and matter. Here, we report the clearcut results of an extensive, ongoing investigation aiming to mathematically digest Maxwell’s equations in virtually all problems based on the three standard building units, dielectric and [...] Read more.

Maxwell’s equations epitomize our knowledge of standard electromagnetic theory in vacuums and matter. Here, we report the clearcut results of an extensive, ongoing investigation aiming to mathematically digest Maxwell’s equations in virtually all problems based on the three standard building units, dielectric and magnetic, found in practice (i.e., spheres, cylinders and plates). Specifically, we address the static/quasi-static case of a linear, homogeneous and isotropic dielectric and magnetic sphere subjected to a DC/low-frequency AC external scalar potential, (vector field, ), of any form, produced by a primary/free source residing outside the sphere. To this end, we introduce an expansion-based mathematical strategy that enables us to obtain immediate access to the response of the dielectric and magnetic sphere, i.e., to the internal scalar potential, (vector field, ), produced by the induced secondary/bound source. Accordingly, the total scalar potential, = + (vector field, = + ), is immediately accessible as well. Our approach provides ready-to-use expressions for and ( and ) in all space, i.e., both inside and outside the dielectric and magnetic sphere, applicable for any form of (). Using these universal expressions, we can obtain and ( and ) in essentially one step, without the need to solve each particular problem of different () every time from scratch. The obtained universal relation between and ( and ) provides a means to tailor the responses of dielectric and magnetic spheres at all instances, thus facilitating applications. Our approach surpasses conventional mathematical procedures that are employed to solve analytically addressable problems of electromagnetism. Full article

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8 pages, 253 KB

Open AccessPerspective

Very High-Energy Cosmic Ray Particles from the Kerr Black Hole at the Galaxy Center

by Orlando Panella, Simone Pacetti, Giorgio Immirzi and Yogendra Srivastava

Condens. Matter 2025, 10(3), 47; https://doi.org/10.3390/condmat10030047 - 23 Aug 2025

Viewed by 278

Abstract

After a just tribute to Guido Barbiellini, we show how the notion of a maximum force (

F_{\max} = c^{4} / (4 G) ≃ 3 \times 10^{43}

Newtons) present on the event horizon of a black hole (BH) can be [...] Read more.

After a just tribute to Guido Barbiellini, we show how the notion of a maximum force (

F_{\max} = c^{4} / (4 G) ≃ 3 \times 10^{43}

Newtons) present on the event horizon of a black hole (BH) can be used in conjunction with the Wilson area rule to obtain the surface confinement of the mass of a BH analogous to the surface confinement of quarks. This is then translated into the central result of the paper that PeV scale protons exist on the surface of the Kerr BH residing at our galactic center, a result in complete agreement with the HAWC Collaboration result of a Pevatron at the galactic center. We conjecture that the supermassive BHs present at the center of most galaxies are not born out of a galactic collapse but that they must have been present since the formation of their hosting galaxy. Full article

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

10 pages, 701 KB

Open AccessArticle

Beyond Wave-Nature Signatures: h-Independent Transport in Strongly-Scattering Quasi-2D Quantum Channels

by Er’el Granot

Condens. Matter 2025, 10(3), 46; https://doi.org/10.3390/condmat10030046 - 14 Aug 2025

Viewed by 252

Abstract

The Landauer-Büttiker formalism provides a fundamental framework for mesoscopic transport, typically expressing conductance in units of the quantum of conductance, e²/h. Here, we present a theoretical study of electron transport in a quasi two-dimensional (2D) quantum wire. This system [...] Read more.

The Landauer-Büttiker formalism provides a fundamental framework for mesoscopic transport, typically expressing conductance in units of the quantum of conductance, e²/h. Here, we present a theoretical study of electron transport in a quasi two-dimensional (2D) quantum wire. This system features a wide transverse confinement and a longitudinal, high-energy, narrow potential barrier. The derivation, performed within the Landauer framework, yields an analytical expression for the total conductance that is explicitly independent of Planck’s constant (h). Instead, the conductance is found to depend solely on the Fermi energy, the electron effective mass, the wire width, and the effective barrier strength. We interpret this as an emergent phenomenon where the explicit signature of the electron’s wave-like nature, commonly manifest through Planck’s constant (h) in the overall scaling of conductance, is effectively absorbed within the energy- and geometry-dependent sum of transmission probabilities. This allows the conductance to be primarily governed by the Fermi energy, representing a ‘state-counting’ quantum parameter rather than more wave-like characteristic. Full article

(This article belongs to the Section Quantum Materials)

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13 pages, 346 KB

Open AccessArticle

The Solution to Hardy’s Paradox

by Ivan Arraut

Condens. Matter 2025, 10(3), 45; https://doi.org/10.3390/condmat10030045 - 10 Aug 2025

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Abstract

By using both the weak-value formulation as well as the standard probabilistic approach, we analyze Hardy’s experiment introducing a complex and dimensionless parameter (

ϵ

), which eliminates the assumption of complete annihilation when both the electron and the positron departing from a [...] Read more.

By using both the weak-value formulation as well as the standard probabilistic approach, we analyze Hardy’s experiment introducing a complex and dimensionless parameter (

ϵ

), which eliminates the assumption of complete annihilation when both the electron and the positron departing from a common origin cross the intersection point P. We then find that the paradox does not exist for all the possible values taken by the parameter. The apparent paradox only appears when

ϵ = 1

, which is just a singular value. In this paper we demonstrate that this particular value is forbidden inside the scenario proposed by the experiment. Full article

(This article belongs to the Section Condensed Matter Theory)

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15 pages, 5436 KB

Open AccessArticle

Effect of Surface Passivation on the Quasi-Two-Dimensional Perovskite X₂Cs_(n−1) Pb_nI_(3n+1)

by Min Li, Haoyan Zheng, Xianliang Ke, Dawei Zhang and Jie Huang

Condens. Matter 2025, 10(3), 44; https://doi.org/10.3390/condmat10030044 - 9 Aug 2025

Viewed by 356

Abstract

The two-dimensional (2D) Ruddlesden–Popper perovskite exhibits superior chemical stability but suffers from compromised photoelectric properties due to the van der Waals gap. This study presents a novel investigation of surface passivation effects on quasi-2D perovskite X₂Cs_n−1Pb_nI_3n+1 [...] Read more.

The two-dimensional (2D) Ruddlesden–Popper perovskite exhibits superior chemical stability but suffers from compromised photoelectric properties due to the van der Waals gap. This study presents a novel investigation of surface passivation effects on quasi-2D perovskite X₂Cs_n−1Pb_nI_3n+1 (n = 1–6; X = MA, FA, PEA) using DFT methods, revealing three key advances: First, we demonstrate that organic cation passivation (MA⁺, FA⁺, PEA⁺) enables exceptional stability improvements, with FA-passivated structures showing optimal stability—a crucial finding for materials design. Second, we identify a critical thickness effect (n > 3) where bandgaps converge to <1.6 eV (approaching bulk values) while maintaining strong absorption, establishing the minimum layer requirement for optimal performance. Third, we reveal that effective masses balance and absorption strengthens significantly when n > 3. These fundamental insights provide a transformative strategy to simultaneously enhance both stability and optoelectronic properties in quasi-2D perovskites. Full article

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11 pages, 223 KB

Open AccessEssay

Beyond Space and Time: Quantum Superposition as a Real-Mental State About Choices

by Antoine Suarez

Condens. Matter 2025, 10(3), 43; https://doi.org/10.3390/condmat10030043 - 6 Aug 2025

Viewed by 626

Abstract

This contribution aims to honour Guido Barbiellini’s profound interest in the interpretation and impact of quantum mechanics by examining the implications of the so-called before–before Experiment on quantum entanglement. This experiment was inspired by talks and discussions with John Bell at CERN. This [...] Read more.

This contribution aims to honour Guido Barbiellini’s profound interest in the interpretation and impact of quantum mechanics by examining the implications of the so-called before–before Experiment on quantum entanglement. This experiment was inspired by talks and discussions with John Bell at CERN. This was during the years when John and Guido co-worked, promoting the mission of the laboratory: “to advance the boundaries of human knowledge”. As the experiment uses measuring devices in motion, it can be considered a complement to entanglement experiments using stationary measuring devices, which have meanwhile been awarded the 2022 Nobel Prize in Physics. The before–before Experiment supports the idea that the quantum realm exists beyond space and time and that the quantum state is a real mental entity concerning choices. As it also leads us to a better understanding of the ‘quantum collapse’ and the measurement process, we pay homage to Guido’s work on detectors, such as his collaborations on the DELPHI experiment at CERN, on cosmic ray detection at the International Space Station, and gamma-ray astrophysics during a large NASA space mission. Full article

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

8 pages, 2120 KB

Open AccessPerspective

Axion Searches at the CERN SPS: From Their Dawn to Current Prospects

by Paolo Crivelli and Martina Mongillo

Condens. Matter 2025, 10(3), 42; https://doi.org/10.3390/condmat10030042 - 5 Aug 2025

Viewed by 448

Abstract

This mini-review traces the evolution of axion searches at the CERN Super Proton Synchrotron (SPS), beginning with the early proposal by Guido Barbiellini in 1982 and culminating in the recent advances of the NA62 and NA64 experiments. We discuss the experimental strategies employed [...] Read more.

This mini-review traces the evolution of axion searches at the CERN Super Proton Synchrotron (SPS), beginning with the early proposal by Guido Barbiellini in 1982 and culminating in the recent advances of the NA62 and NA64 experiments. We discuss the experimental strategies employed in early beam dump searches, the current status of axion and axion-like particle (ALP) searches at the CERN SPS and future directions. This review serves as a tribute to Guido Barbiellini’s scientific legacy and his visionary contributions to this field. Full article

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

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11 pages, 1745 KB

Open AccessArticle

Comprehensive Investigation of Structural and Photocatalytic Properties of Cobalt and Nickel Co-Doped Magnesium Oxide Nanoparticles

by Shafaq Arif, Amna Sarwar and M. S. Anwar

Condens. Matter 2025, 10(3), 41; https://doi.org/10.3390/condmat10030041 - 4 Aug 2025

Viewed by 490

Abstract

Cobalt and Nickel (Co, Ni) co-doped magnesium oxide (MgO) nanoparticles (NPs) have been synthesized using the coprecipitation method. The structural, chemical, and optical properties of the as-synthesized NPs are systematically investigated using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and UV-visible spectroscopy. [...] Read more.

Cobalt and Nickel (Co, Ni) co-doped magnesium oxide (MgO) nanoparticles (NPs) have been synthesized using the coprecipitation method. The structural, chemical, and optical properties of the as-synthesized NPs are systematically investigated using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and UV-visible spectroscopy. It is found that the optical bandgap of co-doped MgO NPs reduces from 2.30 to 1.98 eV (14%) with increasing Ni dopant concentrations up to 7%. The Co_0.05Ni_0.07Mg_0.88O NPs exhibit a high photocatalytic degradation efficiency of 93% for methylene blue dye (MB) under natural sunlight irradiation for 240 min. Our findings indicate that the Co_0.05Ni_xMg_0.95−xO NPs have strong potential for use as photocatalysts in industrial wastewater treatment. Full article

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11 pages, 962 KB

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.

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 the other is positive, i.e., one component is metallic, and the other one is dielectric. Here, we study the effect of anisotropy in

{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 KB

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

Viewed by 550

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 [...] Read more.

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 KB

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

Viewed by 943

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 [...] Read more.

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 KB

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

Viewed by 427

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.

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-j conformal fields on the circle, we derive a discrete spectrum of central charges

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 KB

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 865

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 [...] Read more.

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) – 14 articles

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