Condensed Matter

22 pages, 1738 KB

Open AccessReview

Bridging Quantum Capacitance and Experimental Electrochemical Performance in 2D Materials for Supercapacitors: From Density of States to Device-Level Interpretation

by Maria C. Barrero-Moreno, Abraham Méndez-Reséndiz, Juan C. Carrillo-Rodriguez and Andrés M. Garay-Tapia

Condens. Matter 2026, 11(1), 10; https://doi.org/10.3390/condmat11010010 - 21 Mar 2026

Viewed by 667

Abstract

Two-dimensional (2D) materials, particularly MXenes and transition metal dichalcogenides (TMDs), have attracted intense interest as supercapacitor electrodes due to their high surface area and tunable electronic structure. However, large discrepancies persist between the quantum capacitance values predicted by density functional theory (DFT) calculations [...] Read more.

Two-dimensional (2D) materials, particularly MXenes and transition metal dichalcogenides (TMDs), have attracted intense interest as supercapacitor electrodes due to their high surface area and tunable electronic structure. However, large discrepancies persist between the quantum capacitance values predicted by density functional theory (DFT) calculations and experimentally measured gravimetric capacitances. In this review, we critically analyze DFT methodologies, surface models, normalization strategies, and electrochemical characterization protocols, and compile an extensive dataset of reported MXene and TMD systems to quantify the degree of experimental–theoretical agreement. We show that MXenes typically achieve less than 20% of their predicted capacitance because of restacking, surface terminations, and limited ion accessibility, whereas TMDs exhibit substantially better correspondence, often approaching or exceeding 70% of theoretical values. These results indicate that the theoretical capacitance predicted by DFT is primarily determined by the electronic structure of the material, which defines the upper limit of charge storage, whereas the experimentally achieved capacitance is largely controlled by morphological factors, surface chemistry, and electrode architecture that limit ion accessibility. Full article

(This article belongs to the Special Issue Flexible Matter for Electronics, Photonics, and Energy Conversion)

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11 pages, 516 KB

Open AccessArticle

Two-Dimensional Tunable Reactance Element Free from Electromagnetic Coupling

by Yong Sun and Shigeru Kanemitsu

Condens. Matter 2026, 11(1), 9; https://doi.org/10.3390/condmat11010009 - 2 Mar 2026

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Abstract

A capacitor modeled as a parallel combination of a resistance (

R

) and a capacitance (

C

) exhibits three distinct operating regimes when both parameters depend on the applied voltage (V): a positive-capacitance regime ( [...] Read more.

A capacitor modeled as a parallel combination of a resistance (

R

) and a capacitance (

C

) exhibits three distinct operating regimes when both parameters depend on the applied voltage (V): a positive-capacitance regime (

d R / R > d V / V

), an Ohmic regime (

d R / R = d V / V

), and a negative-capacitance regime (

d R / R < d V / V

). In the limit (

R \to \infty

), the device behaves as a conventional permittivity-based capacitor, whereas in the limit (

R \to 0

), negative capacitance emerges due to nonlinear current–voltage characteristics. To verify this mechanism, we fabricated nanometer-spaced two-electrode structures using multi-walled carbon nanotubes (MWCNTs) and Si crystals. The measurements confirmed negative capacitance consistent with theoretical predictions. Unlike ferroelectric negative capacitance, the effect demonstrated here arises solely from the nonlinear I–V characteristics at the electrode interfaces, without involving any ferroelectric polarization dynamics. This negative capacitance can be interpreted as an equivalent inductance, enabling a two-dimensional tunable reactance element (TDTRE) that operates without electromagnetic coupling and is compatible with conventional IC technologies. Full article

(This article belongs to the Section Physics of Materials)

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11 pages, 5872 KB

Open AccessFeature PaperArticle

Measurements of Electronic Band Structure in CeCoGe₃ by Angle-Resolved Photoemission Spectroscopy

by Robert Prater, Mingkun Chen, Matthew Staab, Sudheer Sreedhar, Journey Byland, Zihao Shen, Sergey Y. Savrasov, Valentin Taufour, Vsevolod Ivanov and Inna Vishik

Condens. Matter 2026, 11(1), 8; https://doi.org/10.3390/condmat11010008 - 25 Feb 2026

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Abstract

In this paper, we present a comprehensive study of the electronic structure of CeCoGe₃ throughout the entire Brillouin zone in the non-magnetic regime using angle-resolved photoemission spectroscopy (ARPES). The electronic structure agrees in large part with first principles calculations, including predicted topological [...] Read more.

In this paper, we present a comprehensive study of the electronic structure of CeCoGe₃ throughout the entire Brillouin zone in the non-magnetic regime using angle-resolved photoemission spectroscopy (ARPES). The electronic structure agrees in large part with first principles calculations, including predicted topological nodal lines. Two new features in the band structure are also observed, namely a surface state and folded bands, the latter of which is argued to originate from a unit cell reconstruction. Full article

(This article belongs to the Special Issue Topological and Quantum Materials for Energy and Information: Spectroscopy and Computation Approaches)

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20 pages, 10183 KB

Open AccessFeature PaperArticle

Laser-Spot Step-Heating Thermography for Non-Destructive Evaluation of Thermal Diffusivity in Apples

by Ginevra Lalle, Alessandro Maurizi, Anna Maria Giusti, Grigore Leahu, Gianmario Cesarini, Emilija Petronijevic, Alesandro Belardini and Roberto Li Voti

Condens. Matter 2026, 11(1), 7; https://doi.org/10.3390/condmat11010007 - 18 Feb 2026

Viewed by 604

Abstract

In this work, thermal imaging is employed to study the opto-thermal response of apples (Malus domestica Borkh.), assessing their post-harvest evolution through the estimation of thermal diffusivity. A non-destructive experimental procedure based on mid-wave infrared (MWIR) thermal camera (3–5 µm) and localized heating [...] Read more.

In this work, thermal imaging is employed to study the opto-thermal response of apples (Malus domestica Borkh.), assessing their post-harvest evolution through the estimation of thermal diffusivity. A non-destructive experimental procedure based on mid-wave infrared (MWIR) thermal camera (3–5 µm) and localized heating with a visible laser is developed, enabling spatially and temporally resolved surface temperature measurements. Temperature fields are recorded at different time points and radial distances from the heated spot. A theoretical model based on Fourier thermal diffusion equation is formulated to describe the spatio-temporal evolution of surface temperature. After validation on a reference sample, the method is applied to Golden and Red Delicious apples over a 28-day storage period at room temperature. Red Delicious apple exhibits higher mean diffusivity values without significant temporal changes, whereas a progressive increase in diffusivity is observed for Golden Delicious apples. These results show that thermal diffusivity is sensitive to post-harvest physiological changes in apple tissue and may be associated with intrinsic properties such as tissue density and water content. By relating laser-induced temperature fields to the estimation of thermal diffusivity, this approach enables the non-destructive, quantitative assessment of thermal diffusivity, showing potential for fruit maturity and quality assessment, which are of high importance in agri-food monitoring applications. Full article

(This article belongs to the Section Spectroscopy and Imaging in Condensed Matter)

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21 pages, 3379 KB

Open AccessArticle

Insights into Neutral vs. Deprotonated Phenol Adsorption on Graphene Oxide

by Jeton Halili, Kledi Xhaxhiu, Nensi Isak, Makfire Sadiku, Arianit Reka, Muhamed Farruku and Avni Berisha

Condens. Matter 2026, 11(1), 6; https://doi.org/10.3390/condmat11010006 - 6 Feb 2026

Cited by 1 | Viewed by 997

Abstract

Water pollution from phenols remains a critical concern due to their persistence, toxicity, and industrial prevalence. Graphene oxide (GOx), with its functional groups and large surface area, offers strong adsorption potential. Using density functional theory (DFT), reduced density gradient (RDG), and quantitative structure–activity [...] Read more.

Water pollution from phenols remains a critical concern due to their persistence, toxicity, and industrial prevalence. Graphene oxide (GOx), with its functional groups and large surface area, offers strong adsorption potential. Using density functional theory (DFT), reduced density gradient (RDG), and quantitative structure–activity relationship (QSAR), we examined how protonation and substituents influence phenol adsorption. Deprotonated phenolates bind more strongly to GO than neutral species via electrostatics and H-bonding. Substituents alter affinity: halogens enhance it, bulky alkyls hinder it, and nitro groups show electron-withdrawing effects. Bisphenolate A displayed multidentate binding. QSAR models reproduced DFT energies with R² > 0.99, enabling fast prediction. These results highlight how pH speciation and substituents govern adsorption on GO, guiding the design of efficient water treatment materials. Full article

(This article belongs to the Special Issue Selected Papers from the 3-Day International Conference on Materials Science (3D-ICOMAS))

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15 pages, 492 KB

Open AccessFeature PaperArticle

Two-Carrier Description of Cuprate Superconductors from NMR

by Daniel Bandur, Abigail Lee, Jakob Nachtigal, Stefan Tsankov and Jürgen Haase

Condens. Matter 2026, 11(1), 5; https://doi.org/10.3390/condmat11010005 - 5 Feb 2026

Viewed by 862

Abstract

Cuprates currently hold the record for the highest temperature superconductivity at ambient pressure, but the microscopic understanding of these materials remains elusive. Here, we utilize nuclear magnetic resonance (NMR) data of planar oxygen and copper from essentially all hole-doped cuprates to provide a [...] Read more.

Cuprates currently hold the record for the highest temperature superconductivity at ambient pressure, but the microscopic understanding of these materials remains elusive. Here, we utilize nuclear magnetic resonance (NMR) data of planar oxygen and copper from essentially all hole-doped cuprates to provide a universal phenomenology relating the NMR spin shifts, which measure the electronic spin polarization at a given nucleus, with the superconducting dome and maximum critical temperature. There appear to be two separate contributions to the spin shift in planar copper, only one of which is seen at the oxygen site, and we associate them with two different types of carriers. Upon disentangling these two components, their relative size is shown to correlate not only with the doping dependence of the superconducting dome but also with the variation in maximum superconducting critical temperature,

T_{c, \max}

, between different families. One of these components is independent of family and resides in the hybridized planar orbitals of Cu and O. The second component, in contrast, is predominately isotropic and encodes the differences between the families. It is thus related to the charge transfer gap and planar hole sharing. Our findings offer universal insight which should prove useful in the continuing development of a comprehensive theory of the cuprates, as well as an indication of how it may be possible to engineer materials with higher critical temperatures. Full article

(This article belongs to the Special Issue Superstripes Physics, 4th Edition)

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12 pages, 2292 KB

Open AccessArticle

Electron Correlation and High-Temperature Superconductivity

by Takeshi Egami

Condens. Matter 2026, 11(1), 4; https://doi.org/10.3390/condmat11010004 - 30 Jan 2026

Viewed by 978

Abstract

Strong electron correlation plays a central role in the high-temperature superconductivity (HTSC) of cuprates. However, to date, research has focused only on its role in spin dynamics and related effects, even though it is becoming increasingly clear that spin alone may not be [...] Read more.

Strong electron correlation plays a central role in the high-temperature superconductivity (HTSC) of cuprates. However, to date, research has focused only on its role in spin dynamics and related effects, even though it is becoming increasingly clear that spin alone may not be sufficient to create HTSC. Here, we discuss a possible role of electron correlation in the Bose–Einstein condensation (BEC) of Cooper pairs. Recently, we succeeded in observing dynamic electron correlation via inelastic X-ray scattering through results presented in real space. We discovered that electron correlations are strongly modified in the plasmon, proving that electron dynamics significantly affect electron correlation. Earlier, we found that in ⁴He, the atom–atom distance in the BE condensate is 10% longer than that in the non-condensate. These results suggest the possibility that the reduction in electron-repulsion energy upon BEC is driving T_c to high values. Thus, electron correlation itself could be the origin of the HTSC phenomenon. Full article

(This article belongs to the Special Issue Superstripes Physics, 4th Edition)

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14 pages, 513 KB

Open AccessReview

Solid-State Detector for FLASH Radiotherapy: Dosimetric Applications and Emerging Concepts

by Pablo P. Yepes

Condens. Matter 2026, 11(1), 3; https://doi.org/10.3390/condmat11010003 - 23 Jan 2026

Viewed by 784

Abstract

The implementation of FLASH Radiotherapy (FLASH-RT), characterized by ultra-high dose rates (UHDRs) frequently exceeding

10^{6}

Gy/s in microsecond pulses, imposes stringent requirements on real-time dosimetry. Conventional ionization chambers suffer severe ion recombination and space-charge limitations under these conditions. This review summarizes the [...] Read more.

The implementation of FLASH Radiotherapy (FLASH-RT), characterized by ultra-high dose rates (UHDRs) frequently exceeding

10^{6}

Gy/s in microsecond pulses, imposes stringent requirements on real-time dosimetry. Conventional ionization chambers suffer severe ion recombination and space-charge limitations under these conditions. This review summarizes the state of SSD technologies—including conventional standard silicon diodes, advanced SiC diodes, Low-Gain Avalanche Detectors (LGADs), and pixel detectors—and compares their performance, linearity, and dynamic range in UHDR environments. Particular attention is devoted to operational modes (integrating vs. counting), saturation mechanisms, and readout electronics, which frequently dominate detector behavior at FLASH conditions. We discuss the experimental results from recent UHDR beamlines and highlight emerging concepts that will shape future clinical translation. 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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15 pages, 5100 KB

Open AccessArticle

First-Principles Study of the Formation and Stability of the Interstitial and Substitutional Hydrogen Impurity in Magnesium Oxide

by A. G. Marinopoulos

Condens. Matter 2026, 11(1), 2; https://doi.org/10.3390/condmat11010002 - 9 Jan 2026

Viewed by 789

Abstract

Hydrogen is frequently incorporated in alkaline-earth oxides during crystal growth or post-deposition annealing. For MgO, several studies in the past showed that interstitial monatomic hydrogen can also favourably bind with oxygen vacancies to form stable substitutional defect complexes (substitutional hydrogen or U-defect centers). [...] Read more.

Hydrogen is frequently incorporated in alkaline-earth oxides during crystal growth or post-deposition annealing. For MgO, several studies in the past showed that interstitial monatomic hydrogen can also favourably bind with oxygen vacancies to form stable substitutional defect complexes (substitutional hydrogen or U-defect centers). The present study reports first-principles density-functional calculations of the formation energies of both interstitial and substitutional forms of the hydrogen impurity in MgO. Determination of the site-resolved densities of electronic states allowed for a detailed identification of the nature of the impurity-induced levels, both in the valence-energy region and inside the band gap of the host. The stability and diffusion mechanisms of both hydrogen defects was also studied with the aid of nudged elastic-band (NEB) calculations. Interstitial hydrogen was found to be an amphoteric defect with the lower formation energy for any realistic environment conditions (temperature and oxygen partial pressure). The NEB calculations showed that it is a fast-diffusing species when it is thermodynamically stable as a positively-charged state (bare proton). In contrast, the hydrogen-vacancy complex is a shallow donor, extremely stable against dissociation and virtually immobile as an isolated defect. Its formation is found to be favoured for a range of mid-gap Fermi-level positions where positively-charged interstitial hydrogen and neutral oxygen vacancies (F centers) are both thermodynamically stable low-energy defects. The present findings are consistent with the established consensus on the electrical activity of hydrogen in MgO as well as with experimental observations reporting the remarkable thermal stability of substitutional hydrogen defects and their ability to act as electron traps. Full article

(This article belongs to the Section Condensed Matter Theory)

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13 pages, 814 KB

Open AccessArticle

Unveiling Bulk Modulus and Stretching Bond Force Constants of Cubic and Wurtzite Boron Nitride Structures: A DFT Study

by Melissa L. Casais-Molina, César A. Cab, Rubén A. Medina-Esquivel and Jorge A. Tapia

Condens. Matter 2026, 11(1), 1; https://doi.org/10.3390/condmat11010001 - 21 Dec 2025

Viewed by 1127

Abstract

The mechanical properties of cubic (c-BN) and wurtzite (w-BN) boron nitride structures were investigated and compared using density functional theory (DFT) with several exchange–correlation functionals. This research focuses on determining the bulk modulus (

B

) and, for the first time, the stretching [...] Read more.

The mechanical properties of cubic (c-BN) and wurtzite (w-BN) boron nitride structures were investigated and compared using density functional theory (DFT) with several exchange–correlation functionals. This research focuses on determining the bulk modulus (

B

) and, for the first time, the stretching bond force constants (

k_{r}

), two fundamental parameters that describe the intrinsic stiffness and elastic resistance of these BN structures. Despite their structural similarity with the same tetrahedral coordination between atoms, c-BN and w-BN exhibit subtle differences in bond strength and compressibility that have not been fully clarified at the atomistic level. By systematically analyzing the influence of hybrid and semi-local functionals, consistent relationship between structural configuration and the predicted

B

and

k_{r}

values of both c-BN and w-BN structures were established and compared. These findings not only validate DFT as a reliable approach for assessing the mechanical properties of BN polymorphs, but also offer key parameters for machine learning and advanced multiscale modeling. Therefore, this theoretical study contributes to understanding the origin of mechanical properties in BN structures and supports their design in applications where a particular hardness and stability are required. Full article

(This article belongs to the Section Physics of Materials)

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Condens. Matter, Volume 11, Issue 1 (March 2026) – 10 articles

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