Search Results (477)

Aiming to develop high-performance flexible electrode materials for dielectric elastomer actuation systems applied to micro-crawling robots, this study proposes multi-dimensional filler composite electrode materials with a methyl vinyl silicone rubber matrix. Three types of conductive fillers—namely, zero-dimensional super-conductive carbon black, one-dimensional single-walled carbon nanotubes, and two-dimensional flaky micron-sized silver powder—were employed to construct a hierarchical multi-dimensional conductive network within the silicone rubber matrix via a three-stage fabrication strategy. The electrical conductivity and conductive stability of the as-prepared composite electrode materials were systematically investigated, where the intrinsic mechanisms and evolutionary laws of material electrical performance variations were analyzed. Furthermore, the effects of fillers with different dimensional morphologies on the comprehensive properties of the composites at each fabrication stage were explored, and the optimal filler dosage for each component was determined. Microstructural observations of the staged conductive network formation further verified the rationality of the stage-based functional design model. The optimized composite electrode delivers an initial electrical conductivity of 1.5 × 10⁴ S/m, with only a 14.9% conductivity attenuation under 50% tensile strain, demonstrating excellent electromechanical stability. Moreover, a prototype micro-crawling robot was fabricated using the optimized composite electrode, achieving a maximum linear crawling speed of 8 mm/s. These experimental results validate the feasibility and superiority of the proposed multi-dimensional filler composite strategy. This work provides a novel technical approach for the design and development of high-performance flexible electrode materials for flexible electronic and micro-robotic actuation applications. Full article

Second-generation high-temperature superconducting tapes (2G HTS; SuperPower Inc., Glenville, NY, USA) based on GdBCO (GdBa₂Cu₃O_7−δ, where δ denotes oxygen deficiency) were aged at −26.4 °C, +2 °C, and room temperature (RT) to evaluate the degradation of their superconducting properties. HTS tapes stored at RT exhibited a significantly higher deterioration rate compared to those maintained at lower temperatures. Laser-induced breakdown spectroscopy (LIBS) analysis demonstrated a gradual reduction in the effective chemical depth-profiling length over time, indicating a correlation between the degradation mechanism and the reduction in the effective volumetric density of the GdBCO superconducting layer. These findings imply that oxygen diffusion or redistribution processes substantially contribute to the long-term degradation of GdBCO-based HTS tapes. Full article

A superconducting high-entropy alloy (HEA) Nb_0.67(TiZrHf)_0.33 powder was successfully synthesized via mechanical alloying for the first time. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, magnetic measurements, and specific heat were used to investigate its structural and physical properties. The alloy was crystallized in a single-phase body-centered cubic structure with a small amount of non-magnetic impurities coming from ball milling. Specific heat data confirms the presence of bulk superconductivity in the as-synthesized state, with the broadness of the thermodynamic anomaly reflecting the significant chemical disorder and distribution of critical temperatures typical of HEAs. $T_c$ is in the range 6–7.5 K, and the upper critical field $\mu 0H_{\mathrm{c}2}$ is in the range 6.4–7.6 T. These results demonstrate that mechanical synthesis is a viable route for producing superconducting HEA powders, which are promising candidates for consolidation via sintering and provide a robust platform for investigating superconductivity in highly disordered systems. Full article

Binary neutron star mergers and proto-neutron stars provide unique environments where dense matter is hot, lepton-rich, and potentially undergoes a transition from hadronic to deconfined quark matter. We investigate the thermodynamics and stellar properties of hybrid matter under such conditions. The hadronic phase is described within a covariant density functional framework, while the quark phase is modeled using a Nambu–Jona-Lasinio (NJL) model that includes repulsive vector interactions, the axial $U_A\left(1\right)$-breaking ’t Hooft determinant interaction, and two-flavor color-superconducting (2SC) pairing. The phase transition between hadronic and quark matter is constructed using a mixed-phase prescription that enforces baryon and lepton number conservation, allowing us to follow thermodynamic trajectories at fixed entropy per baryon and a fixed lepton fraction. We analyze the phase structure of dense matter at a finite temperature and study the composition of the hadronic, mixed, and quark phases in both neutrino-trapped and neutrino-free regimes. Our results show that neutrino trapping significantly modifies the particle composition and shifts the onset of deconfinement to higher densities. The mixed phase exhibits a density-dependent pressure due to the presence of multiple conserved charges. Using the resulting equations of state, we compute static stellar configurations and examine the influence of the temperature and lepton content on the mass–radius relation in hybrid stars. Hot, neutrino-rich configurations are found to have larger radii and slightly higher maximum masses than their cold counterparts. As the star cools and deleptonizes, its radius contracts at an approximately constant baryonic mass, potentially triggering changes in the internal phase structure. These results highlight the roles of color superconductivity, lepton trapping, and thermal effects in shaping the structure and evolution of hybrid stars in transient astrophysical environments. Full article

The electronic properties of high-temperature superconducting cuprates are encoded in NMR data. Without microscopic theory, reliable NMR phenomenologies are in demand. Here we make use of the extensive literature data to develop a different understanding of the cuprates from the shifts of the ${\mathrm{CuO}}_2$ plane. The Cu shift analysis is based only on the symmetry of the two Cu hyperfine couplings, without assumptions about their size. We use an anisotropic $A_{\alpha }$ and isotropic B, as from atomic Cu orbitals, and find two spin components (A- and B-spins) that explain all the shift data. The components differ in size and temperature dependence according to simple rules. Upon doping the cuprates, metallic B-spin appears above a pseudogap temperature, which is shared with the A-spin. Further doping decreases the pseudogap temperature and increases the B-spin, but less so the A-spin. The apparent linear rate of increase in the density of states of the B-spin with doping is nearly threefold above $x=0.20$, where the pseudogap disappears. The pseudogap temperature is a measure of the coupling between A and B, which suppresses the shifts but not nuclear relaxation. Spin-singlet pairing involves A and B according to three simple condensation rates, which will be discussed. The optimal $T_{\mathrm{c}}$ demands a special match between A and B. However, the shifts do not simply predict the highest $T_{\mathrm{c}}$ of all cuprates, in contrast to nuclear relaxation anisotropy and charge sharing between planar Cu and O. Relations to other probes are discussed. Full article

The solidification process is crucial for preparing high-performance superconductors and is strongly dependent on the characteristics of the starting powder, including particle size, morphology, and phase purity. This review concisely examines the study on four key superconductors: REBCO, Bi-2212, FeSeTe, and MgB₂. In REBCO, additives such as CeO₂, Pt, or BaO₂ powder can refine the RE-211 phase. In Bi-2212, Pb doping stabilizes the high-T_c phase. For FeSeTe, doping with F or Co modifies phase separation and introduces Δκ pinning. Meanwhile, in MgB₂, the incorporation of SiC nanoparticles powder generates effective pinning centers. Concurrently, processing conditions exert a decisive influence on the final microstructure, as demonstrated by the TSMG/TSIG route in REBCO, partial melting parameters for Bi-2212, specific cooling protocols and thermal treatments for FeSeTe, and optimized sintering and post-annealing processes for MgB₂. Future research directions should prioritize fundamental understanding of phase separation mechanisms during powder processing, development of multi-component doping strategies for powder modification, and advancement of scalable powder processing routes for practical conductor architectures. Full article

FeSe-based superconductors have become a hot topic with regard to high-temperature superconductor mechanisms and applications due to their broadly adjustable critical temperatures and the underlying rich physics. This has led to the emergence of numerous experimental approaches for regulating important critical parameters, particularly superconducting transition temperature, T_c. Owing to its powerful and effective control, electrochemical intercalation has become a widely adopted technique for tailoring the chemical and physical properties of layered materials in recent years. This short review concisely introduces FeSe-based superconductors and an electrochemical intercalation method and summarizes the research progress that has been made in utilizing this method to modulate the structure and superconductivity of FeSe-based materials. Full article

Under the deformation potential model, the superconducting phenomenon in ABC-stacked multilayer graphene under a vertical electric field is investigated using linear combination operators and unitary transformation methods. Through the deformation potential model applied to a linear continuous medium, the effect of the external electric field is converted into the deformation potential energy of the crystal. Deformation potential phonons (LA phonons) act as propagators, generating electron–electron interactions. As the electric field increases, the ratio of the electric displacement vector to the dielectric function ($D/\epsilon$) rises, leading to an increase in the electron ground-state energy, the opening of the band gap, and an enhancement of the attractive electron–electron interaction. With further increases in the external electric field, the deformation potential constant of the crystal ($D_l$) increases. When the phonon vibration frequency ($\omega$) is around 8.5 THz, and the conditions are satisfied—where the wave vectors of different LA phonons are equal in magnitude and opposite in direction, and the electron spins are opposite—the attractive electron–electron interaction reaches its maximum ($H_{eff}$), resulting in the emergence of superconductivity. Our study also provides a new perspective for understanding the unique quantum properties—such as strong correlations, superconductivity, and ferromagnetism—in different stacking configurations like AB, ABC, and ABCA. Full article

Recently, CuBa₂Ca₃Cu₄O_10+δ (Cu1234) has garnered significant interest owing to its distinctive triple-high superconducting properties (118K high T_c, combined with high J_c and high H_irr at liquid nitrogen temperature at ambient pressure) and potential for practical applications. The Cu1234 is initially synthesized at high pressures and is stable at a room temperature range but tends to decompose upon heating above 300 °C at ambient. In this study, we investigate the thermal stability of Cu1234 through annealing at various temperatures and oxygen pressures. It is found that Cu1234 starts to decompose at approximately 350 °C, 550 °C, and 600 °C when annealed at 1 bar, 100 bar, and 150 bar oxygen pressure, respectively. Prior to decomposition, however, the superconducting properties remain largely unchanged. The decrease in oxygen occupancy within the BaO layer of the BaCuO_3−δ charge reservoir block is proposed to be the primary cause of the structural instability of Cu1234, while higher oxygen pressures retard oxygen loss from this block. Our result suggests that the decomposition temperature of Cu1234 will further increase with higher oxygen pressure, e.g., possibly to 800 °C at 260 bar if a linear extrapolation is adopted. This study offers important insights for fabricating Cu1234 tapes via the powder-in-tube method. Full article

Experimental results suggest a feasible strategy for tuning the superconducting properties of MgB₂ through the incorporation of an electroluminescent inhomogeneous phase. By introducing GaP electroluminescent inhomogeneous phases into MgB₂, the effects of emission intensity variation on the sample structure, superconducting transition temperature, electrical transport behavior, and magnetic properties were systematically investigated. The results show that, at a fixed GaP addition level, the superconducting transition temperature T_c increases steadily from 38.2 K to 39.6 K with increasing emission intensity of the inhomogeneous phase, corresponding to a maximum enhancement of approximately 1.4 K. Meanwhile, the zero-resistance temperature shifts upward synchronously, indicating that the entire superconducting transition region moves toward higher temperatures. Raman measurements show that the peak position and linewidth of the E_2g phonon mode evolve systematically with emission intensity, while the electron–phonon coupling parameter λ exhibits a trend consistent with that of T_c. In addition, the nanoscale dispersed distribution of the GaP inhomogeneous phase, together with the interface/defect structures it introduces, appears to promote sample densification and enhance flux pinning, resulting in an increase in the critical current density J_c by approximately 69% at 20 K in self-field and an enhancement of the irreversibility field H_irr by about 31.5%. These results suggest that, beyond the effect of static inhomogeneous-phase incorporation, the luminescence-activated state under bias excitation is likely involved in modulating the superconducting response of MgB₂. This work provides a new experimental perspective for synergistically regulating the properties of conventional superconductors through the combined effects of inhomogeneous phases and excited states. Full article

Experimental studies on the spontaneous nucleon emission in nuclei around the drip line enable us to explore new isotopes or resonant states, and to reveal exotic structures and decay properties of nuclei located far from the $\mathsf{\beta }$ stability line; consequently, they are of critical importance for probing limits of nuclear stability and understanding nucleon–nucleon interactions under extreme conditions of isospin asymmetry. With the radioactive isotope beam ²⁰Mg provided by the National Superconducting Cyclotron Laboratory at Michigan State University, we studied the proton decays of nuclei around the proton drip line at $A\sim 20$ mass region. Complete-kinematics measurements were performed for proton decays of one-proton resonant states in ¹⁸Na, two-proton resonant states in ²⁰Mg, three-proton resonant states in ²¹Al, and four-proton resonant states in ¹⁸Mg, yielding decay energy spectra for all four nuclei. With the invariant mass method, the ground state of ¹⁸Na was firmly identified, clarifying previous ambiguities of its position. The isotope ¹⁸Mg, which is located two neutrons beyond the proton drip line, was experimentally observed for the first time. Multi-body correlation analysis of emitted protons from ²⁰Mg, ²¹Al, and ¹⁸Mg, combined with Monte Carlo simulations, reveals that the identified resonant states in ²⁰Mg and ²¹Al predominantly decay via two and three sequential steps of $1p$ emission, respectively, whereas the ¹⁸Mg ground state decays mainly through a two-step cascade of prompt $2p$ emission. Full article

As one of the three fundamental modes of heat transfer, thermal radiation has long attracted interest due to its independence from a medium and its strong temperature dependence. In extreme environments such as deep space exploration and cryogenic engineering, thermal radiation often becomes the dominant heat transfer mechanism. Consequently, the radiative properties of materials are crucial for achieving precise thermal control, directly influencing the thermal stability and overall performance of advanced systems, including space probes, cryogenic devices, and superconducting components operating under high-vacuum and low-temperature conditions. This paper provides a systematic review of the physical mechanisms, key factors affecting emissivity, major measurement methods, and technological developments related to material radiative properties at cryogenic temperatures. Particular attention is given to experimental methods and techniques describing material radiative behavior, along with a comparative analysis of the suitability of different measurement techniques for cryogenic applications. Finally, the study highlights the significant practical value of this research for fields such as aerospace, precision electronics, and cryogenic instrumentation, aiming to offer insights for optimizing cryogenic thermal management and guiding the design of novel functional materials. Full article

Since the discovery of iron-based superconductors nearly two decades ago, significant advancements have been made, including the enhancement of the superconducting transition temperature ($T_c$) to above 100 K. However, the underlying pairing mechanism remains an unresolved enigma. In this article, we present experimental developments in iron-based superconductors, focusing on their unique properties and the complexities involved in their behavior. We discuss the recently announced electron–differential phonon coupling model, which aims to provide a framework to calculate the T_c of iron-based superconductors, but raises questions about its applicability to all iron-based superconductors. We selectively analyze several compounds within the major iron-based families to assess their compatibility with the electron–differential phonon coupling model. By comparing experimental data with theoretical predictions, we identify which superconductors align with the model and which do not. Furthermore, our findings reveal several key reasons behind the discrepancies in calculating $T_c$ for those iron-based materials that fall outside the theoretical expectations. Despite this, the pairing mechanism of iron-based superconductors remains an open question. Full article

The effect of ionising irradiation up to 30 MGy on the mechanical and dielectric properties of different polymers for potential use in particle accelerators and detectors was compared in this study. The materials studied include the high-performance polymers PEEK, PPS and PEI; pure anhydride- and amine-based epoxy resin systems for coil impregnation and adhesive bonding; glass fibre epoxy composites; and FDM, SLA and SLS 3D-printed materials and polyurethanes. Gamma irradiation was applied in ambient air at an approximate dose rate of 2 kGy/h. Dose-dependent radiation damage was monitored by three-point bending tests, Shore A hardness, tensile stress–strain measurements and breakdown voltage tests in liquid nitrogen. Radiation hardness was rated according to two criteria: the dose at which the initial mechanical strength is halved and the dose at which the mechanical strength is reduced below a certain threshold value. The degradation of the breakdown voltage was preceded by the degradation of mechanical properties. Full article

Superconducting transition-edge sensors (TESs) exhibit excellent single-photon detection performance. The quantum efficiency (QE), which quantifies the probability that an incident photon is absorbed and converted into a measurable signal, is strongly governed by the optical properties of the constituent thin films. Specifically, for typical TES device architectures where optical transmission is negligible, maximizing the QE requires the minimization of surface reflectance to ensure high photon absorptance. In this work, we systematically study how anodic oxidation modifies the optical response of superconducting titanium (Ti) thin films that are relevant for TES devices. Anodization is carried out under well-controlled constant-current conditions in an aqueous electrolyte containing ammonium pentaborate and ethylene glycol. Experimentally, we show that anodic oxidation substantially reduces the ultraviolet (UV) reflectance and induces a monotonic redshift of the reflectance minimum as the anodic oxidation cutoff voltage (V_ocv) increases. Finite-difference time-domain (FDTD) simulations based on spectroscopic ellipsometry data reproduce the measured spectra with good fidelity for most samples, validating the extracted optical constants. By comparing samples prepared at different current densities and oxidation times, we identified V_ocv as the primary parameter controlling the reflectance response, because it determines the thickness and effective optical properties of the anodic TiO_x layer. Under optimized conditions, reflectance values below 1% in the 320.9–340.2 nm wavelength range and below 2% in the 316.3–346.3 nm range are achieved, indicating a significant enhancement in potential absorptance. These results demonstrate that anodic oxidation provides a simple, post-fabrication, and voltage-tunable route for engineering the UV optical response of Ti-based TES structures and for enhancing their potential QE by suppressing reflection losses. Full article