Physical Sciences

Abstract: Artificial spin ice systems have provided powerful platforms for exploring frustrated magnetism and emergent phenomena. However, nanoscale fabrication constraints limit the direct manipulation and real-time visualization of individual magnetic elements for square ice model. Macroscopic mechanical analogues overcome these limitations by enabling direct observation and flexible control of local interactions. Nevertheless, how geometry-tuned intra-unit interactions regulate global ordering in frustrated systems remains poorly understood. Here, we construct a “macroscopic square ice” experimental platform to investigate this problem, using the unit gap l as a tunable geometric parameter while fixing the vertex gap d at 1.1 mm. By directly monitoring magnetic domain evolution and vertex-type distributions, we reveal a non-monotonic order–disorder–order transition driven by the competition between intra-unit and inter-vertex interactions. This work provides direct experimental insight into the role of geometry-controlled local interactions in governing collective ordering and offers a visible approach for studying emergent behaviors in frustrated systems.

Abstract: Temperature-dependent electrical resistivity ρ(T) in cuprate, iron-based, and nickelate superconductors represents one of unresolved problems in modern solid-state physics, because of the high absolute value of ρ(T), which, in many cases, exceeds the Ioffe-Rigel criterion, and a large difference in the ρ(T) shape for samples with different doping. Here I show that the nearest neighbours parallel resistivity model (arXiv: 2607.23484) can well describe the in-plane resistivity ρ_ab(T) in iron-based superconductors (IBS) of type 11, 111, 122, 1111, 1144 and 42214 in which the spin density wave phase or nematic order is suppressed by doping. The model is based on the postulate that ρ_ab(T) is a sum of two parallel conduction channels, where one channel is described by the Bloch-Grüneisen equation and the other by the Arrhenius hopping equation. Consequently, the variety of ρ_ab(T) in the IBS is explained as a variation of the Debye temperature Θ_D and the hopping activation energy E_a. The derived Debye temperatures were used to estimate the electron-phonon coupling constant in the studied IBS.

Abstract: TiO₂ nanotubes and ZnO thin films were investigated as oxide-based memristive systems for resistive switching and state-retention applications under variable environmental conditions. TiO₂ nanotubes were synthesized by electrochemical anodization, while ZnO thin films were deposited on Ti substrates by DC magnetron sputtering. Structural, chemical, and morphological properties were examined by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. TiO₂ exhibited a vertically aligned nanotubular morphology, whereas ZnO showed a granular thin-film surface. Electrical characterization was performed using Au top electrodes and Ti as the bottom electrode under atmospheric pressure and high-vacuum conditions, with temperature varied from 353 K down to 77 K. Both materials exhibited hysteretic current–voltage behavior associated with resistive switching, although their response was strongly influenced by morphology, defect distribution, and environmental conditions. TiO₂ nanotubes showed stable high- and low-resistance states, with an ON/OFF ratio of approximately 4.65, indicating robust state retention. The observed behavior was attributed to oxygen-vacancy-mediated transport, filament stabilization, and interface effects. These results highlight the relevance of comparing TiO₂ and ZnO nanostructures for identifying oxide systems capable of maintaining resistive states under temperature and pressure variations, supporting their potential for low-power non-volatile memory applications.

Abstract:

In this work, TiO₂ and TiO₂:Co nanotubes were fabricated via electrochemical anodization, using Ti (99.99% purity) and Ti/Co foils as the anode and cathode. Cobalt was deposited onto the Ti foils using the DC magnetron sputtering technique under a working pressure of 2.5×10⁻² Torr. The resulting nanotubes exhibited wall nodes and an average length of ~300 nm. The synthesized structures were characterized by X-ray diffraction (XRD), identifying anatase as the predominant phase, accompanied by an amorphous halo. Two types of MSM devices were fabricated to study bulk and surface conduction: a transverse configuration (TE/(TiO₂, TiO₂:Co)/Ti), with top electrodes (TE) Al or Au, and a coplanar configuration (Al/TiO₂/Al). Topographic study was analyzed using Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM) in tapping mode. The device behavior is mainly governed by the TE/ TiO₂ junction due to the absence of an energy barrier at the TiO₂/Ti interface. All samples exhibit asymmetric I-V behavior with higher conduction under positive bias. The Au/ TiO₂/Ti device showed the lowest resistance among Ti BE structures, displaying Schottky behavior with low reverse current leakage and a shift in the zero-current crossing depending on the scan direction. Barrier heights near the zero-current crossing, calculated via the thermionic emission model, were 0.91 eV and 0.70 eV for reverse and forward directions, respectively. Ideality factors and series resistance exceeded 6.8 and 40 kΩ, suggesting additional transport mechanisms. In addition, magnetization as a function of the applied field was realized to TiO₂:Co nanotubes evidencing the ferromagnetic-like behavior.

Abstract: Decoherence is the operative crisis of quantum computing——every architecture confronts it, and every proposed remedy carries a hidden cost in overhead, gap requirement, or temperature constraint. This paper derives, in full algebraic detail and without unexplained transitions, a holographic decoherence-suppression mechanism rooted in the AdS$_3$/CFT$_2$ correspondence, showing that the bulk--boundary geometry of three-dimensional anti-de Sitter space acts as a geometric filter that exponentially screens environmental noise from qubit degrees of freedom encoded in the helical edge modes of topological insulators and in trapped-ion chains. Starting from the chiral Luttinger liquid Hamiltonian of a quantum spin Hall edge, we derive the Virasoro algebra with central charge \(c\), identify the bosonic density fluctuation \(\delta\rho(x,t)\) as the boundary trace of a bulk dilaton field \(\phi(z,x,t)\), solve the dilaton equation of motion step by step to obtain the bulk-to-boundary propagator, and couple it to the Lindblad master equation to derive the modified decoherence rate:\[ \gamma_{\text{holo}} = \gamma_{\text{std}} \exp\!\left(-\frac{2\pi \Delta_n}{c}\frac{l}{\xi}\right), \qquad \frac{T_{\text{std}}^{\text{holo}}}{T_{\text{std}}^{\text{std}}} = \exp\!\left(\frac{\xi}{6}\ln\frac{l}{\xi}\right). \]. Every intermediate numerical estimate in the paper is anchored to independently measured material parameters: Fermi velocity \(v_{\mathrm{F}}\), bulk gap \(\Delta_{\mathrm{gap}}\), and coherence length \(\xi = \hbar v_{\mathrm{F}} / \Delta_{\mathrm{gap}}\). We derive explicit density--density correlation functions, dynamical structure factors, and out-of-time-order correlators (OTOCs), each carrying logarithmic holographic corrections testable by scanning tunneling microscopy, angle-resolved photoemission spectroscopy (ARPES), and Ramsey interferometry. Gate fidelities exceeding \(99.9\%\) are shown to be achievable for Majorana-based qubits when the geometric ratio satisfies \[L/\xi \gtrsim 15 \quad \text{with} \quad c \geq 2. \] Three experimental platforms are analyzed quantitatively: \(\mathrm{Bi}_2\mathrm{Se}_3\) topological insulator edges, \(\mathrm{HgTe}/\mathrm{CdTe}\) quantum wells, and \(^{171}\mathrm{Yb}^+\) trapped-ion chains, with detailed measurement protocols for each.

Abstract: Whether the plasticity of silicon at high temperatures originates from dislocation slip or solid-state phase transition remains difficult to investigate directly through experimental observation due to its microscopic nature. Using molecular dynamics simulations, we investigated the deformation behavior of silicon crystals along four typical crystallographic directions at a reduced temperature of T/Tm = 0.88. The results indicate that prior to yielding, compressive stress induces uniform amorphization throughout the crystal. Once the critical stress is exceeded, Shockley partial dislocations nucleate on the {111} crystal planes, initiating plastic flow, while the amorphous phase undergoes recrystallization during the stress relaxation. These findings demonstrate that at high temperatures, the plasticity of silicon involves both stress-assisted amorphization and dislocation-mediated plasticity, which occur sequentially rather than competing with one another. This study provides atomic-scale guidance for suppressing dislocation defects in the directional solidification growth of polycrystalline silicon.

Abstract: The physical properties of hydrogen-bonded systems spanning zero to three dimensions—covering low-dimensional ices, bulk liquid water and biological hydration layers—are characterized by disjoint theoretical formalisms, without a consistent quantitative analytical toolkit. This work constructs an axiomatic Topological Relational Field Theory (TRFT) rooted in the core axiom that relational connections precede discrete material entities. Geometric dimension \(d∈[0,3]\) is defined as a continuously adjustable control parameter. A three-term dimension-scaling free-energy functional is formulated, the physical quantity of dimensional-confinement generalized force is introduced, and manifold compactification regularization is adopted to eliminate mathematical divergences at the d→0 limit. The theory derives universal global thermodynamic stability conditions and constructs piecewise kinetic functionals. Rigorous mathematical proof verifies d_(c,ph)=2 as the critical dimension of phonon softening, which marks the boundary of a second-order topological phase transition. This work clearly distinguishes topological soft modes from intrinsically unstable imaginary phonon frequencies, thereby revising the oversimplified single stability criterion in conventional lattice dynamics. Dimensional lifting-reduction operator algebra is established, and a linking-number conservation theorem is proven for all d≤1 closed-loop manifolds undergoing smooth deformation without hydrogen-bond cleavage. A spatiotemporal duality theorem is further proposed, which unifies the spatial boundary confinement of solid ice and finite temporal observation restriction of liquid water into an identical topological constraint mechanism. The “topological constraint” introduced herein for liquid water specifically refers to the dynamic geometric confinement imposed by the finite observation window τ_obs<∞. Numerous transient closed-loop geometries do exist within liquid water; however, their topological validity is bounded by the observation window. Closed loops act as effective carriers of topological constraints and participate in thermodynamic statistics only when τ_obs≲τ_esc, and their statistical weights are collectively governed by the hydrogen-bond breaking probability peff(T). This “transient-topology” effect differs fundamentally from the “permanent geometric topology” found in solid ice—with respect to the temporal persistence of constraints and statistical weighting. The triple-helix interlocked closed loop (Lk = ± 3), the optimal space-filling configuration identified in the fourth DFT study, is employed in the present work merely as a numerical illustration of transient topology, rather than serving as the definitional prerequisite for topological constraints in liquid water. The resultant universal equation of state takes solid-state DFT outputs as primary inputs, with only one single calibration point at atmospheric-pressure water density maximum to fix the effective hydrogen-bond energy. Homogeneous quantitative interpretations are simultaneously obtained for six century-long puzzles: the 4 °C liquid water density maximum (T_max=277.15 K), the 228 K critical singularity of supercooled water, abnormally high static dielectric permittivity under ambient conditions, freestanding thermodynamic stability of substrate-free low-dimensional ice, systematic misjudgment induced by imaginary-frequency phonon diagnostics, and Pauling residual entropy for nanoconfined hydrogen networks. The framework achieves closed theoretical coverage of solid, liquid and gaseous phases at the zero-density gas limit. All derivations are based on pure mathematical deduction, with no empirical fitting parameters extracted from liquid experimental data; all characteristic transition temperatures of the system can be solved a priori solely via topological parameters of solid hydrogen-bond lattices. The mathematical architecture of TRFT exhibits formal isomorphism with the phase diagrams of cuprate high-temperature superconductors and percolation equations describing cosmic large-scale matter distributions, indicating broad cross-disciplinary application prospects and laying a conceptual foundation for subsequent theoretical and experimental research.

Abstract: Hinge states are a characteristic boundary manifestation of three-dimensional higherorder topological phases, but identifying them in realistic Wannier tight-binding models requires a sequence of choices that is rarely automated: selection of a target bulk gap, construction of multiple mixed-boundary geometries, sparse solution of large wire Hamiltonians, and discrimination of corner-localized spectral weight from surface and bulk weight. We present HingeStateDetector, a computational method that performs this sequence using a wannier90_hr.dat Hamiltonian and a POSCAR as its mandatory inputs. The program parses and validates the real-space hopping model, estimates sampled global bulk gaps, constructs wires that are finite along two lattice directions and periodic along the third, and uses shift--invert sparse diagonalization near the selected gap. For every eigenstate it reports corner-, edge-, and interior-cell probabilities and builds an energy- and cell-resolved local density of states (LDOS). An automatic mode screens all three lattice axes, while machinereadable JSON and NPZ outputs retain the parameters and numerical evidence needed for convergence studies. We verify the implementation with the chiral hinge model of Benalcazar, Bernevig, and Hughes: only the expected periodic direction is classified as positive, four corner-localized branches traverse the bulk gap, and the interior weight falls below one percent for converged cross sections. A 30-orbital spinful Bi$_2$Se$_3$ Hamiltonian distributed with WannierTools provides a realistic stress test. In addition, a 128-orbital spinful Hamiltonian for the experimentally established higher-order topological insulator \(\alpha\)-Bi$_4$Br$_4$ supplies a real-material positive control. The detector selects the quasi-one-dimensional chain direction and retains corner-dominated in-gap candidates as the cross section grows from $3\times3$ to $5\times5$. These results establish an axis-resolved, quantitative route from Wannier interpolation to finite-boundary evidence, while showing explicitly why hinge localization alone is not a bulk topological invariant

Abstract:

Collective motion happens when many individuals move together using only local rules, with no leader. The Vicsek model captures this through a noise-driven transition from order to disorder, but it usually assumes that agents can see in every direction and that the crowd stays at one fixed density, neither of which is realistic. We ask whether an agent's field of view (\(\alpha\)) and the population density (N) work together to shape the character of this transition, meaning how sharply a flock falls apart rather than only at what noise level it does. We add a forward vision cone to the Vicsek model and run a full sweep of 4 field-of-view angles, 3 densities, and 11 noise levels, with 30 seeds each (3960 runs). For each run we fit a logistic curve to the order parameter as noise rises and read off two numbers: the steepness \(k\) and the break-point \(\eta_c\). A two-way ANOVA shows that field of view and density work together to set where the flock breaks, but not how sharply it breaks; sharpness is shaped by density and field of view separately, with no interaction between them. Our hypothesis predicted an interaction on the sharpness, so it is only partly supported: density does not make up for a narrow field of view the way we expected. The result separates two parts of robustness that are easy to confuse and shows which one sensing range actually affects.

Abstract: The establishment of wave mechanics theory in microwave absorption research carries significance that transcends mere error correction. While refuting impedance matching theory eliminates false explanatory frameworks, the deeper contribution of wave mechanics theory lies in fundamentally redirecting research methodology and objectives. This essay argues that the true value of wave mechanics theory emerges not from what it negates—the impedance matching framework, the treatment of return loss (RL) as material property, the attribution of film thickness effects to material structure—but from what it enables: a reoriented research paradigm that investigates optimal relationships between complex permittivity, complex permeability, frequency response characteristics, and microwave absorption performance. The profound contribution of wave mechanics theory is methodological: it transforms microwave absorption research from a descriptive cataloging of material structures into a rigorous investigation of how material composition and structural design influence the frequency response characteristics of electromagnetic properties. This reorientation represents the genuine theoretical advancement that the field requires.

Abstract: This article presents the design, construction, and calibration of a portable instrument capable of measuring the solar spectrum in the visible region (430–650 nm), as well a UVA, UVB, and UVC radiation, while also determining the ultraviolet radiation index. The hardware was constructed by integrating a Raspberry Pi 4B, a Raspberry Pi HQ camera coupled to a spectroscope for solar spectrum analysis, and an AS7331 sensor for UV radiation measurement. The control software was developed in Python and includes a graphical user interface that displays the solar spectrum and UVA, UVB, and UVC radiation levels, in addition to calculating the ultraviolet index from UVB-band measurements. The instrument was calibrated using a mercury (Hg) spectral lamp, a reference spectrometer, and commercial UVA and UVB radiation meters. The prototype spectrometer was calibrated and adjusted in the city of Arequipa. During this stage, the equations required to convert the digital signals from the sensors into radiometric units were determined, and the measurement uncertainty of the instrument was obtained. Finally, the instrument was evaluated under field conditions at three locations situated at different altitudes: Camaná (0 m a.s.l.), Arequipa (2330 m a.s.l.), and Sumbay (4100 m a.s.l.). The spectrometer recorded irradiance values of 111.2 W/m², 670.7 W/m², and 643.1 W/m² in Camaná, Arequipa, and Sumbay, respectively, and exhibited a maximum deviation of 15.8 W/m² from the measurements obtained with the reference instrument. Likewise, maximum differences of 0.27 mW/cm², 0.02 mW/cm², and 0.01 mW/cm² were observed for UVA, UVB, and UVC radiation measurements, respectively. These differences were not significant relative to the order of magnitude of the measurements obtained. In addition, the ultraviolet radiation index was found to reach values of up to 21 in Sumbay, posing a risk to the population of the region. The results showed that the solar spectrum and UV radiation measurements obtained with the constructed instrument were proportional to those recorded by the reference spectrometer and commercial UV meters, demonstrating its reliability and feasibility as a measurement instrument.

Abstract: This report focuses on cognitive gaps for pressure dependence of the melting temperature, presenting: (i) the coherent discussion on T_m (P) behaviour both for ‘Hard’ Matter (‘standard’ solid state) and Soft Matter systems, to reveal the importance of intermolecular interactions strength, (ii) the model picture linking systems with (dT_m)⁄(dP>0), (dT_m)⁄(dP< 0) and T_m (P) curve maximum; which also shows the relevance of the negative pressures domain, (iii) the ultimate validation test of the recent ‘universal’ scaling of T_m (P) pattern derived by Trachenko [Phys. Rev. E 2024, 109, 034122] against empirical data. The evidence for ‘Hard Matter’ focuses on systems relevant for the semiconductor industry, but yet under-discussed: Silicon, Germanium, and Gallium Nitride. For Soft Matter, these include unique polymeric systems and liquid-crystalline pentylcyanobiphenyl (5CB). For the latter, symmetry-selected melting/freezing takes place. Finally, the specific case of graphite and diamond a discussed. The report includes an innovative solution for melting temperature under-pressure detection.

Abstract: Temperature-dependent electrical resistivity ρ(T) is one of the most common types of experimental data analysed in condensed matter physics. For one group of pure metals, the actinides, experimental ρ(T) curves differ radically from one another to the point that there is no unified theoretical approach to understanding and fitting ρ(T) data in these elements. First-principles calculations result in ρ(T) curves that differ from experimental data, even qualitatively. In an attempt to unravel this long-standing problem, here I propose a simple model that accurately fits the ρ(T) data for eight phases of elemental actinides (from thorium (Th) to curium (Cm)) for which experimental data are publicly available to date. The model is based on the concept of two parallel conduction channels: one is described by the Bloch-Grüneisen equation, which is associated with the classical electron-phonon dissipation mechanism, and the other by the Arrhenius equation, which is associated with the nearest-neighbor hopping (NNH) conductivity. Debye temperatures Θ_D derived from application of the model to ρ(T) data for eight elemental actinide phases agree well with reported values deduced from heat capacity measurements. For neptunium (Np) a maximum Arrhenius activation energy (among all actinides) of was derived. The model was also successfully applied to ρ(T) data measured on d-phase plutonium-based alloys Pu-Ce and Pu-Ce-Ga.

Abstract: Exceptional points (EPs) offer new paradigms in non-Hermitian physics, but their realization has long relied on active gain-and-loss mechanisms. In our previous work, we established that clusters of innumerable EP loci can be achieved within purely real-parameter passive systems under single-fixed and semi-definite boundaries. However, extending this framework to double-ended boundaries introduces highly coupled transcendental boundary conditions, thereby increasing the complexity of the conventional exact tracking. This study addresses this challenge by considering a both-fixed two-degree-of-freedom (2DOF) passive system. Through rigorous algebraic proofs, we achieve an analytical mapping of the global coalescing trajectories, specifically encompassing the complex degenerate roots (loci of EPs) and real double roots (loci of critical damping points) within a purely real state-space via discrete boundary points. We demonstrate that the dual-boundary constraints fundamentally morph the topologies of the EP clusters, giving rise to novel localized phase transitions and critical damping loci. These exact analytical boundaries reveal that dual confinement acts not as a restriction but as an unprecedented design flexibility to precisely manipulate non-Hermitian singularities, even under purely real-parameter passive conditions. Our exact formulation provides a foundational theoretical framework that is potentially applicable to the environmentally robust passive tuning of next-generation device architectures, ranging from micro-scale electromechanical resonators to high-frequency communication components, offering a passive alternative to mitigate the instabilities inherent in conventional active non-Hermitian systems.

Abstract: Numerous studies on non-Hermitian physics have remained confined to isolated exceptional points (EPs) and relied on complex parameters to analyze their physical characteristics [1–20]. Because manipulating such complex variables poses significant engineering constraints in real-world applications, recent efforts have focused on shifting the operational framework towards pure real-parameter spaces or continuous regimes [21–23]. To overcome these limitations, a recent study investigated a purely real-parameter passive system, successfully elucidating an L-surface where innumerable loci of EPs cluster together [24]. To demonstrate that this phenomenon is not an accidental occurrence but a generalized physical trait, we applied this framework to a three-degree-of-freedom semi-definite damped system, thereby establishing its systemic universality. Importantly, we discovered that the inertia of this bare primary mass acts as a critical topological switch: varying its scale governs whether the system coalesces into the L-surface or branches into alternative physical regimes. By treating this ungrounded mass as a key scaling parameter, we define the exact boundaries that map these diverse topological states. Given its high configurability, this framework opens up new avenues for multi-functional wave guiding, adaptive energy harvesting, and highly sensitive topological sensors, expanding the practical utility of non-Hermitian systems previously explored [24].

Abstract: Research on exceptional points (EPs) as singularities, where eigenvalues and eigenvectors coalesce, has sparked a revolution in non-Hermitian physics [1–7], offering unprecedented sensitivity and wave manipulation. Previous studies have predominantly focused on isolated points in the complex plane [8–12], often relying on nonphysical complex parameters or active gain–loss modulation. However, such approaches introduce significant system complexity and hinder scalability, leaving the realization of continuous EP structures in purely passive, real-world systems an open challenge [13–18]. To address this challenge, this study reports the discovery of an EP surface within a purely passive, real-parameter, canonical two-degree-of-freedom (2DOF) damped system. A hidden physical landscape was unveiled, termed the L-surface, representing clusters of loci of innumerable EPs. Leveraging the L-surface derived from exact analytical solutions, this study identified and validated fundamental topological phenomena, including topological jump, imprint, and nucleation, all of which were previously obscured by numerical noise [19–23]. The comprehensive analysis and precise identification of this manifold required a physical parameter precision of 100 decimal places. This regime has been conventionally dismissed as mere numerical artifacts in standard 64-bit double-precision floating-point formats. The L-surface provides a robust foundation for next-generation ultrasensitive sensing and energy dissipation across frontiers, ranging from quantum computing [24–26] to advanced biosensing [27, 28], extending its transformative impact to the broader realms of electronics [29, 30] and optics [31–33].

Abstract: In this short perspective, we analyze the different linear response functions relevant to surface diffusion studied by helium atom scattering, organizing them around a single object: the intermediate scattering function (ISF), which is also a characteristic function (CF) in the sense of probability theory. This organizing role of the CF is, to our knowledge, not made explicit elsewhere in the surface-diffusion literature, even though the time exponential function it predicts in the diffusive regime is a special case of the classical continuous-time-random-walk (CTRW) theory. Special emphasis is placed on this diffusive regime, established at times much greater than the inverse of the friction coefficient, where quantum features of the diffusion process are washed out. We show how the entire hierarchy of response functions—the after-effect function, the generalized susceptibility, the relaxation function, and the Green function—can be written directly in terms of the time moments of the ISF at \(t=0\), and how the Pauli master equation and the Chudley-Elliott (CE) jump model follow as particular lattice realizations of a general compound-Poisson process. The extension to finite surface coverage is discussed within the interacting single adsorbate (ISA) model.

Abstract: Crystalline solids melt at well-defined material-specific temperatures T_m via first-order phase transitions, whereas glasses undergo continuous transformations from solid to molten states at glass transition temperatures T_g, resembling second-order transitions. Despite extensive study, the microscopic origin of this distinction remains unveiled. In this work, both melting and glass transition are described within a unified framework based on analysis of thermally activated breakings of chemical bonds, treated as elementary excitations of condensed matter termed configurons. The increasing concentration of configurons leads to a percolation transition corresponding to loss of mechanical rigidity of an elastic solid whose atoms are connected via chemical bonds. Configurons are delocalized and mobile in crystals, enabling their condensation and consequent latent heat release, whereas in glasses they are localized (Anderson localization), suppressing condensation and yielding a continuous transition from solid to molten states. The proposed framework provides a unified physical interpretation of phase transitions.

Abstract: This research investigates the systematic nanomechanical behavior of tetragraphene-based nanotubes (TGCNTs) using reactive classical molecular dynamics (CMD) simulations with the AIREBO-Morse potential. Tetragraphene is a novel carbon allotrope characterized by a unique mixture of sp2 and sp3 hybridization. We analyzed the nanomechanical properties of zigzag-like TGCNTs under uniaxial tensile loading, systematically examining the effects of chirality, diameter, length, and temperature ranging from 300 K to 2100 K. Our results reveal a distinct nanostructural degradation at high temperatures, where the nanotubes completely lose their structural stability above 1500 K. Under mechanical strain, the stress-strain curves highlight a strong dependence on chirality. The (0,N) TGCNTs exhibit brittle behavior, characterized by a short, nearly linear curve that terminates abruptly at a rapid fracture point without significant plastic deformation. In contrast, the (N,0) TGCNTs demonstrate remarkable ductility and superelasticity. This is evidenced by a distinct plateau effect with constant stress up to 20% strain, followed by strain hardening until ultimate fracture at over 40% strain, indicating a stress-induced structural phase transition. To map their transverse elasticity, the Poisson’s ratio (ν) was evaluated within the elastic regime, revealing an ultra-low value of ν=0.07 for the TGCNT (0,10) in close agreement with density functional theory (DFT) benchmarks, contrasting with an anomalously high value of ν=1.19 for the TGCNT (14,0) due to severe chiral anisotropy. The calculated Young’s modulus values range from 2714.10 to 3166.20 GPa.Å for (N,0) TGCNTs and 1886.70 to 2324.30 GPa.Å for (0,N) TGCNTs. These insights into the nanostructure-property relationships of TGCNTs provide essential design guidelines for their application in flexible electronics, nanocomposites, and nanoscale shock-absorbing devices.

Abstract: InGaN/GaN quantum wells on polar substrates exhibit a pronounced quan-tum-confined Stark effect, which significantly limits their efficiency as light emitters. Surprisingly, this detrimental effect is significantly reduced when wider wells (above 10 nm) are used; their emission kinetics are the central focus of this work. A time range spanning 9 orders of magnitude, from picoseconds to milliseconds, is explored through various experiments. This includes experiments on the optical visualization of slow decays of charge in the ground states (called “dark charge”) in the millisecond range, experiments on radiative recombination of excited states in the nanosecond range and on the relaxation of hot carriers in the picosecond range. All data are explained within the framework of qualitative and semi-quantitative models. The highly diverse kinet-ics of ground and excited states is due to the fact, that the ground states of electrons and holes have negligible overlap and screen the built-in field, are optically inactive, and recombine nonradiatively in milliseconds. Meanwhile, when the field is screened, the excited states recombine radiatively in the picosecond/nanosecond range. The pulses of photo- and electro-luminescence depend strongly on the excitation period. The application of negative-voltage pulses allows to deplete the well from charge and generates short pulses of light.