Physical Sciences

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.

Abstract: Quantum computing is a potential solution to the limitations of current computing devices, but the need for superconductivity has led to prohibitively high operational costs and energy consumption. A major bottleneck is the low critical temperature needed to achieve superconductivity. Here, a quantum diode system is proposed that utilizes a circuit approach to achieve superconductivity at room temperature. Two opposed p–n diodes are connected to another junction in one of two configurations (A and B systems) that cancels the electric field in the depletion layer of each diode, which causes electrons and holes to reappear and prevents their recombination. Thus, the combination energy of a Cooper pair (i.e., exciton) is very strong, and Bose–Einstein condensation is maintained even at room temperature. When a bias voltage is applied between the A and B systems, Lorentz conservation imparts momentum (i.e., wavenumber) to the carriers in the absence of any internal voltage, so a superconducting bias current density appears without any need for cooling. Numerical calculations including many-body interactions revealed that constant phases for the macroscopic wavefunctions of p- and n-type semiconductors converged, which confirmed that Bose–Einstein condensation and the Meissner effect occurred. Moreover, the quantum diode system exhibited rectification characteristics and a switching speed on the order of 10⁻¹⁴ s. These switching properties and large superconducting bias current were used to develop NOT and NAND gates with direct quantum correlations that are unaffected by random and thermal noise.

Abstract: The exact time-space correlation function of the 1D Glauber-Ising model, quenched to temperature T = 0 and on a semi-open lattice of finite size N, is obtained. This also allows to deduce the exact empty-interval probability of the dual 1D coagulation-diffusion process on a periodic finite ring and to reproduce the long-time decay of the particle concentration. These results are consistent with the generic expectations of dynamical finite-size scaling theory.

Abstract: This paper presents the design, construction, and experimental evaluation of a low-cost, portable solar tracking system for monitoring ultraviolet solar radiation in real time. It integrates a Raspberry Pi Zero 2W as the embedded control unit; an AS7331 spectral sensor to measure UVA, UVB, and UVC irradiance; two 270° servomotors to position the system toward the sun; a NEO-6M GPS module to geolocate the system; and a DS3231 real-time clock to synchronize the time. To enable autonomous outdoor operation, a multistage power supply architecture based on a solar panel, rechargeable battery, LM2596, and MP1584EN DC-DC regulators was implemented. The tracking algorithm uses astronomical equations to estimate solar azimuth and elevation and updates the sensor orientation during daylight hours. This allows the UV sensor to remain approximately normal to the incoming solar radiation. Experimental tests were conducted in Arequipa, Peru. The recorded data included UVA, UVB, and UVC irradiance; sensor temperature; geographic coordinates; time; and solar angles. The measured UV profiles exhibited the anticipated diurnal behavior: maximum values around solar noon, higher UVA levels than UVB levels, and minimal UVC levels due to atmospheric absorption. We compared the radiometric response with reference information from EarthKit, PVGIS 5.3, SAMPA, and a Davis Vantage Pro 2 weather station. We evaluated the solar positioning performance against Stellarium, NOAA, and the NREL Solar Position Algorithm. The prototype has an azimuth error of less than 0.009% and an elevation error of less than 0.4% compared to the NREL SPA, NOAA and Stellarium Systems. The results demonstrate that the proposed prototype provides a portable, customizable, and affordable platform for solar UV monitoring, educational instrumentation, and field-based solar resource assessment.

Abstract: Our earlier X-ray and neutron scattering data on TiO₂-P₂O₅ glasses with minor Al₂O₃ impurities are re-examined with some modification. Then, it is compared with recent results. There, it is reported that triply coordinated oxygens in the TiO₆ octahedra cause unusual distortions. Here, these effects are discussed more thoroughly. Triply coordinated oxygens enforce short cation-cation distances. The associated repulsions drive distortions, which are facilitated by the second-order Jahn-Teller effect of the d⁰ transition element Ti⁴⁺. The Ti⁴⁺ cations shift away from their octahedral centers. It is compared with GeO₂-P₂O₅ glasses. The size of Ge is similar to that of Ti, but a GeO₆ unit does not suffer distortions. According to these specifics, different ranges of glass formation are observed.

Abstract: Magnetic hyperthermia relies on the ability of magnetic nanoparticles (MNPs) to dissipate heat under alternating magnetic fields, with the heating efficiency commonly quantified through the specific loss power (SLP). Accurate estimation of SLP requires realistic mod-eling of the dynamic magnetic response of nanoparticle ensembles, particularly in the fer-romagnetic single-domain regime where hysteresis losses dominate. In the present work, we developed a computational framework in Mathematica based on the thermally acti-vated Stoner–Wohlfarth model to simulate dynamic hysteresis loops and estimate SLP in ensembles of non-interacting magnetic nanoparticles. The model incorporates experimen-tally relevant distributions of particle diameter, magnetic anisotropy, and easy-axis orien-tation, enabling realistic representation of nanoparticle polydispersity and orientation disorder. Thermal activation was introduced through Arrhenius-type Néel switching probabilities, while the dynamic magnetization evolution was obtained numerically through solution of the corresponding rate equations. The framework was tested for mag-netite nanoparticles, one of the most widely used materials in magnetic hyperthermia, considering typical single-domain ferromagnetic particle sizes in the range of 15–30 nm and effective anisotropy values representative of experimentally reported systems. Simula-tions were performed under clinically relevant alternating magnetic fields with ampli-tudes up to 24 kA/m and frequencies ranging from 100 to 765 kHz. The model successfully reproduced dynamic hysteresis loop evolution and enabled systematic investigation of the influence of nanoparticle size, anisotropy, and orientation distributions on loop shape, symmetry, and SLP. The developed code provides a computationally accessible tool for re-searchers working in magnetic hyperthermia, allowing direct connection between micro-scopic nanoparticle properties and macroscopic heating performance. By enabling para-metric mapping of dynamic hysteresis behavior and SLP dependence, the framework may support the rational optimization of magnetic nanoparticle systems for biomedical hyper-thermia applications.

Abstract: High-entropy transition metal carbides combine ultrahigh hardness, excellent thermal stability, and intrinsic structural disorder, making them attractive for extreme-environment applications. Using density functional theory in the generalized gradient approximation (GGA-PBE) as implemented in the ABINIT package, we systematically calculate the electronic structure and bulk modulus B of a series of (TiZrHf-X)C compositions (X = Sc, V, Nb, Ta, Mo, W) with varying average d-electron count per metal site (ndest). A 24-atom rock-salt (B1) supercell with numerical-annealing relaxation of atomic positions is employed. The calculated DOS for group IV carbides TiC, ZrC, and HfC reveals a strikingly similar electronic structure: in all three cases the Fermi level is located within a wide pseudogap—responsible for the wide carbon nonstoichiometry range—and falls precisely on a small local peak resembling a Van Hove singularity, which promotes vacancy formation even at low temperatures. Qualitatively similar DOS profiles are found for all HECs studied, indicating that this electronic stabilization mechanism persists in multi-component systems. The bulk modulus increases monotonically with ndest from 209±1 GPa for (TiZrHfSc)C to 269±2 GPa for (TiZrHfW)C. At fixed ndest, heavier homologue metals (Ta > Nb > V; W > Mo) yield higher B due to greater core-electron Pauli repulsion. A single metal vacancy reduces B by approximately 21–35 GPa and simultaneously increases configurational entropy, suggesting that metal vacancies function as an additional thermodynamic stabilizing component of the high-entropy compound.

Abstract: A rheological replacement model of a coupled-field continuum induces a constitutive 1-form whose primitive on a star-shaped reversible state space is a thermodynamic potential from which the full constitutive set is recovered by differentiation. The existence of the primitive is equivalent to a single symmetry condition on the constitutive Jacobian; in coupled-field problems that condition is exactly the family of Maxwell relations between the coupled effects. Truesdell's principle of equipresence and the thermodynamic driving forces of the internal variables are consequences of the same construction; the residual dissipation inequality appears as the remaining part of the Clausius--Duhem inequality after all process-independent contributions have been absorbed into the potential.

Abstract: We find a mapping between the attractive Fermi-Hubbard model and the repulsive Bose-Hubbard model at finite temperature and at imaginary chemical potential μ=iθ. We show, by using a large N-expansion, that the partition functions of the two models are related by a simple shift θ→θ+π. This condition maps the BCS–BEC crossover of attractive fermions to a Bose–Fermi crossover (fermion-like occupation) of repulsive bosons. Central feature of this correspondence plays the thermal kernel g(βE,ϕ), whose analytic continuation gB(βE,ϕ)=gF(βE,ϕ+π) governs the bosonic and fermionic sectors. Interestingly, we are able to find that the special angles ϕ=2π/3,4π/3 for fermions correspond to ϕ=π/3,5π/3 for bosons, marking the boundaries of a universal thermal window. We further argue that the present mechanism shows that fermionization can occur at finite interaction strength through a thermodynamic effect induced by the imaginary chemical potential. This suggests that it is a new way of fermionization (not a change in statistics but a fermion-like behaviour) unlike the Tonks–Girardeau limit, where fermionization arises from an infinite repulsive interaction and anyonic or Floquet-engineered systems where transmutation emerges from modified statistics or dynamics. Essentially, the phase ϕ is a statistical parameter; by twisting the thermal phase, it generates fermion-like behaviour without hard-core constraints or infinite repulsion but only by using thermodynamics. We derive the gap equation and number equation for the bosonic model, highlighting the role of the imaginary chemical potential as a statistical regulator. Our results provide a unified framework for understanding crossovers in interacting lattice systems.

Abstract: We propose a mechanically programmable nanoscale Chern valve based on an altermagnet–topologicalinsulator (AM–TI) heterostructure, where thin altermagnetic electrodes impose an anisotropic exchange mass on the surface states of a few-quintuple-layer topological-insulator channel. Periodic strain, delivered for example by integrated piezoelectric or surface-acoustic-wave actuators, modulates the inplane crystalline phase of the altermagnetic order and renormalizes the twofold and fourfold interfacial exchange harmonics through zeroth-order Bessel functions. This amplitude-selective renormalization produces re-entrant Chern plateaus, Hall and thermoelectric polarity inversions, and quantized adiabatic charge pumping with winding number changing from 0 to 2. For representative RuO₂/Bi₂Se₃ parameters, the induced gaps remain in the meV range, while MHz mechanical driving places the system deeply within the adiabatic regime. The predicted signatures are directly accessible in nanoscale Hall-bar geometries through the strain-amplitude dependence of transverse Hall response, gate-tracked thermoelectric Hall response, and the collapse of topological sectors near Bessel zeros. The proposed mechanism therefore provides a low-frequency, on-chip route to mechanically controlled topological transport in nano-spintronic AM–TI devices, without optical Floquet driving or net magnetization reversal.

Abstract: We report the first successful synthesis of millimeter-sized single crystals of high-entropy perovskite manganites with the composition (La_0.25Pr_0.25Sm_0.25Gd_0.25)_1-xCa_xMnO₃ (x = 0.3, 0.4, 0.5). Single crystals exceeding 2 mm in size were grown via a flux method using a PbF₂/PbO/B₂O₃ system. The X-ray diffraction patterns exhibit only (0k0) series reflections, indicating strong preferred orientation and high-quality single-crystal character. Scanning electron microscopy reveals dense, grain-boundary-free surfaces. Energy-dispersive X-ray spectroscopy elemental mapping shows uniform distribution of all constituent elements without detectable segregation or secondary phases, confirming the formation of a true high-entropy solid solution in single-crystal form. To the best of our knowledge, based on the publicly searchable literature, this is the first report of bulk single-crystalline high-entropy perovskite oxide. This breakthrough provides a much-needed single crystal experimental platform for systematically investigating the intrinsic magnetotransport mechanisms of compositionally complex strongly correlated oxides, free from grain-boundary interference.

Abstract: Ultrastrong magnetic fields, ranging from 100~T to 1,000~T, are generated exclusively by destructive pulsed magnets. While various generation methods exist, this review focuses on the Single-Turn Coil (STC) and Electromagnetic Flux Compression (EMFC) techniques, which provide optimal environments for high-precision measurements in materials science. First, we present recent technological breakthroughs in the EMFC method that have successfully achieved fields exceeding 1,000~T. We then describe specialized measurement infrastructures for magneto-optics, magnetization, and magneto-transport, highlighting the development of miniaturized all-plastic cryostats and custom sample holders designed for the dual extremes of cryogenic temperatures and megagauss fields. Representative physical phenomena revealed through these techniques are discussed, including quantum phase transitions in frustrated magnets, Aharonov--Bohm effects in carbon nanotubes, and semiconductor-to-metal transitions in strongly correlated systems. Furthermore, we address emerging measurement platforms such as magnetostriction, specific heat, and ultrasound velocity. Throughout this review, we emphasize the instrumentation and experimental refinements that ensure reliable data acquisition in the ultrastrong pulsed field regime.

Abstract: This article describes the development of a compact and affordable variable temperature NMRinstrument designed primarily to measure dynamic molecular motions in solids and liquids. The instrument consists of Lab-Tools’ Mk4 palm-top time-domain NMR spectrometer fitted with a Peltier-cooled variable temperature probe inside a shimmed Halbach magnet. Measurement of NMR relaxation times T₁, T₂, T_1ρ are possible over the temperature range −20^◦C to 70^◦C with cooling and heating rates, and data acquisition controlled from an integrated mini-PC. The overall footprint of the instrument is roughly that of a shoe box making both in-the-field and bench-top measurements possible. Applications of this instrument include measuring the pore size distribution in porous rocks, the viscosity of oils and tars trapped in porous rock, the properties of polymers, and the viscosity of the liquid components of foods (e.g. fruits, vegetables and seeds). Results of test measurements on calibrated oils and olive oil are presented together with measurements of the molecular mobility in a sold polymer.

Abstract: Nanoscale conductors and interfaces frequently exhibit anomalous AC transport behavior and enhanced superconducting critical temperatures that are not fully captured by conventional electron-phonon descriptions. In this exploratory work, we consider a complementary mechanism based on the possible inertial response of a Z₃-graded vacuum sector to time-varying electromagnetic fields. Within this speculative phenomenological framework, surface criticality is tentatively proposed as a mechanism that may drive high-energy vacuum modes toward low-energy collective excitations at surfaces and interfaces, giving rise to an approximate coherence length ξ_vac∼70 nm. This geometric length scale, if physically meaningful, could influence effective conductivity in the non-local regime and might contribute to observed features such as high-frequency skin depth saturation and interface-driven T_c enhancement. Preliminary evaluations based on the algebraic structure suggest qualitative consistency with certain experimental observations in high-purity metals and nanowire systems, although we emphasize that these consistencies may be coincidental. The framework is offered as a tentative, exploratory perspective on mesoscopic anomalies, with the aim of stimulating further discussion and investigation into possible connections between algebraic high-energy structures and low-energy quantum materials phenomena.

Abstract: By making periodic thru-holes in a suspended film, the phonon system can be modified. Motivated by the BCS theory, the technique -- so-called phonon engineering -- was applied to a metallic niobium sheet. It was found that its electrical resistance dropped to zero at 175 K, and the zero-resistance state persisted up to 290 K in the subsequent warming process. Despite the initial motivation, neither these high transition temperatures nor the phase transition with thermal hysteresis can be accounted for by the BCS theory. Therefore, we abandon the BCS theory. Instead, it turns out that the metallic holey sheet is partly oxidized to form a niobium-oxygen square lattice, which has points of resemblance to a copper-oxygen plane, the fundamental component of cuprate high-T_c superconductors. Therefore, the pairing mechanism underlying this study should be related to that of cuprate high-T_c superconductors, which we may not yet understand. In addition to the electrical results of zero resistance, the holey sheet exhibited a decrease in magnetization upon cooling, i.e., the Meissner effect. Moreover, the remnant magnetization was clearly detected at 300 K, which can only be attributed to persistent currents flowing in a superconducting sample. Thus, this study meets the established criteria for a conclusive demonstration of true superconductivity. Finally, the superconducting transition with the unambiguous thermal hysteresis is discussed. According to Halperin, Lubensky, and Ma, or HLM for short, any superconducting transition must always be first order with thermal hysteresis because of the intrinsic fluctuating magnetic field. The HLM theory is very compatible with the highly oriented system harboring two-dimensional superconductivity.

Abstract: Attenuated total reflection terahertz time-domain spectroscopy (THz-TDS ATR) was employed to investigate the dielectric response of water–acetone mixtures over the full molar concentration range. The ATR configuration enabled stable measurements in a controlled and nearly closed environment, minimizing acetone evaporation and allowing reliable characterization of this highly volatile binary system. The complex dielectric function, retrieved in the 0.4–1.6 THz range, was analyzed by means of a double Cole–Cole model, which provides a more consistent description of the mixtures than a simple Debye-based approach. A strongly nonlinear dependence on composition was observed, with the highest sensitivity in the water-rich region, where even small amounts of acetone produce a marked change in both the real and imaginary parts of the dielectric function. The extracted parameters indicate that acetone primarily suppresses the slow, cooperative relaxation channel associated with the hydrogen-bond network of water, whereas the faster channel remains comparatively less affected, consistent with its more local intermolecular origin. The evolution of the Kirkwood–Fröhlich correlation factors and of the broadening parameters further supports a progressive transition from a highly correlated hydrogen-bonded liquid to a structurally heterogeneous and weakly cooperative dipolar environment. These results demonstrate that THz-TDS ATR is a sensitive tool for probing intermolecular reorganization in aqueous binary mixtures and provide a physically grounded framework for the detection of acetone and other volatile hydrogen-bond-active species in water-based systems.

Abstract: The presence of Cu³⁺ cations and oxygen vacancies (VO) in the electrospun CuO nanofibers was identified by X-ray photoelectron spectroscopy (XPS) from the Cu 2p₃/₂ and O 1s core-level spectra, respectively. A Cu³⁺-related superlattice was observed using nano-beam electron diffraction (NBD). The chemical composition of the two samples thermally treated at 600 °C (CuO600) and 700 °C (CuO700) was further corroborated using the geometrical topofactor method. For comparison, bulk CuO was also analyzed. XPS peak fitting of the Cu 2p and O 1s regions was performed using an SVSC-type background and two-parameter Tougaard function. X-ray diffraction (XRD) confirmed the presence of the tenorite and cuprite phases and enabled crystallite size estimation (FullProf). The average crystallite size ranged from 20.59 ± 0.06 nm to 31.06 ± 0.06 nm, in good agreement with High Resolution Transmission Electron Microscope, HR-TEM, measurements (14.98 ± 0.34 nm and 36.10 ± 0.94 nm). Therefore, we identify that Cu³⁺ and oxygen vacancies in these nanofibers plays a crucial role in optimizing their future applications in the electronic and catalytic fields.