Transition Temperature Research Articles

Valley-Contrasting Linear Dichroism and Excitonic Condensation in LaOBiS2.

In conjunction with the first-principles calculations, we confirm the fascinating valley-selective linear dichroism and the possibility of excitonic condensation in multiatomic-layer LaOBiS2 of a tetragonal lattice by the effective tight-binding model and many-body perturbation theory. In LaOBiS2, which indicates a spontaneous valley polarization due to crystalline symmetry reduction rather than conventional time-reversal symmetry breaking, we unravel that the excitons in X and X' valleys exclusively coupled to x- and y-linearly polarized lights, respectively. In sharp contrast to coupled quantum wells and van der Waals architectures, a new type of spatially indirect exciton is identified in single-crystal LaOBiS2, manifesting itself as an engaging platform for investigating the excitonic Bose-Einstein condensation (BEC) and superfluidity. In light of large binding energy, large radius, and small effective mass of the exciton, the transition temperature for BEC and superfluidity achieves record-high values of 325.1 and 81.3 K, respectively.

Tuning the interfacial transport behavior in a superconducting van der Waals heterostructure

The interaction between the metallic and superconducting components at the interface of superconductor–normal metal (S-N) systems enables a variety of quantum phenomena, including the Josephson effect, Andreev reflection, and proximity-induced superconductivity, which are of significant interest both theoretically and practically. Nevertheless, due to varying physical mechanisms, achieving and fine-tuning multiple such phenomena within a single S-N system continues to be a challenge. In this work, we employ NbSe2 and WTe2 to fabricate an S-N-S heterostructure. Below the superconducting transition temperature of NbSe2, two distinct resistance-temperature behaviors are observed: a continuous decrease in junction resistance with temperature decrease, indicative of the superconducting proximity effect and consistent with the BCS model, and an increase in resistance attributed to competition between Andreev reflection (AR) and normal reflection at a low-transparency interface, which can be suppressed by applying a small bias current or a magnetic field. Our results indicate the signature of the coexistence of proximity-induced superconductivity with AR in the measured S-N-S heterojunction, demonstrating the tunability of charge carrier transport behavior at the interface. This finding enhances our understanding of such systems and holds potential for the development of superconducting electronics, quantum computing, and energy harvesting technologies.

Josephson coupling in lanthanum-based cuprate superlattices

In most anisotropic compounds such as bismuth-based layered cuprate perovskites, the supercurrent across the blocking layer is of Josephson type, and a single crystal forms a natural stack of Josephson junctions. Here, we report on the evidence of Josephson-like transport in an artificial cuprate superlattice composed of 10 LaSrCuO–LaCuO repeats, creating a superlattice of junctions, where LCO is a superconducting Mott insulator and LSCO is an overdoped metal. The superlattice has been designed with a long period of d = L + W = 5.28 nm, with L and W being the thicknesses of LCO and LSCO units, respectively, and is in the underdoped regime with an average doping level of ⟨δ⟩ = 0.11. Quantum-size effects and Rashba spin–orbit coupling are controlled by L/d = 0.75, with a quasi-2D superconducting transition temperature of 41 K and a c-axis coherence length of about 1.5 nm. Measurements at very low temperatures show evidence of Josephson phase dynamics consistent with very low Josephson coupling and a phase diffusion regime, thus explaining why Josephson coupling in LSCO superlattices has been so elusive. The tuning of LSCO superlattices in the Josephson regime enriches the phase diagram of HTS.

Microscopic dynamics of enhanced glass-forming ability with minor oxygen addition in bulk metallic glasses.

Minor oxygen addition has been proposed as a promising strategy to enhance the performance of metallic glasses, particularly their glass-forming ability. In this work, we investigate the microscopic dynamics of a CuZr glass former with oxygen content up to 2 at. % using molecular dynamics simulations based on specially developed neural network interatomic potentials. Our findings indicate a gradual increase in the glass transition temperature with oxygen addition, with an anomalous peak at 0.4 at. % O. We reveal an anti-correlation of kinetic fragility and dynamic heterogeneity behind this unusual rise, where the system exhibits reduced kinetic fragility alongside more significant dynamic heterogeneity. Using the continuous time random walk method, we show that at 0.4 at. % O, a highly mobile Cu atomic layer forms around O-Zr clusters, resulting in notable dynamic heterogeneity. This dynamic behavior is closely linked to the bonding pattern within the O-Zr network, particularly favoring the configuration with edge and surface sharing. In addition, such structures contribute to a more compact O-Zr network, leading to lower kinetic fragility. These findings provide detailed insights into the microscopic dynamics behind the effects of minor oxygen additions.

Superionic conduit of alkaline earth metals confined by two-dimensional boron–carbon layers

Superionic conductors feature fast super-ion diffusion in the solid-state framework, making them ideal materials for safe, high-performing electrolytes. It is, therefore, in hot pursuit of seeking solid-state electrolyte materials with high energy density and flexible operation conditions. Here, we verified a class of two-dimensional superionic conduction in A(BC)2, in which A are alkaline earth metals such as Be, Mg, and Ca, and boron–carbon (BC) form graphene-like layers. Our first-principles molecular dynamics simulation, boosted by high-accuracy machine-leaning potentials, shows that alkaline metal becomes super-ions under high-temperature conditions, moving freely between BC layers. Differences in superionic conduit lead to the diffusion in Be(BC)2 driven by the vacancy mechanism. In contrast, the diffusion in Mg(BC)2 and Ca(BC)2 is jointly driven by both the vacancy and cooperative mechanisms. We demonstrate that the superionic transition temperature is controlled by the deficiency of mobile super-ions, tuning from 1300 to 1600 K, with up to 2.5% cation defects. With superior thermal stability, these two-dimensional compounds are promising electrolyte materials with ultrahigh heat resistivity capable of operating under high-temperature environments such as deep drills and aerospace devices.

Resolving the electronic ground state of La3Ni2O7-δ films

The recent discovery of a superconductivity signature in La3Ni2O7-δ under a pressure of 14 GPa, with a superconducting transition temperature of around 80 K, has attracted considerable attention. An important aspect of investigating electronic structures is discerning the extent to which the electronic ground state of La3Ni2O7-δ resembles the parent state of the cuprate superconductor, a charge transfer insulator with long-range antiferromagnetism. Through X-ray absorption spectroscopy, we reveal the influence of oxygen ligands on the electronic ground states of the Ni ions, displaying a charge transfer nature akin to cuprate but with distinct orbital configurations. Additionally, in La3Ni2O7-δ films, we detect a superlattice reflection (1/4, 1/4, L) at the Ni L absorption edge using resonant X-ray scattering measurements. Further examination of the resonance profile indicates that the reflection originates from the Ni d orbitals. By evaluating the reflection’s azimuthal angle dependence, we confirm the presence of collinear antiferromagnetic spin ordering and charge-like anisotropy ordered with the same periodicity. Our findings reveal a microscopic relationship between these two components in the temperature dependence of the scattering intensity of the reflection. This investigation enriches our understanding of high-temperature superconductivity in La3Ni2O7-δ under high pressure.

Crystallization behavior of smelting slag for recovery of platinum group metals from spent automotive catalysts and preparation of foamed glass-ceramics

Crystallization behavior of smelting slag for recovery of platinum group metals from spent automotive catalysts and preparation of foamed glass-ceramics

Nonconventional phosphorus-based tertiary amine curing agent enabling the high fire safety, outstanding tensile strength and high glass transition temperature of epoxy resin

Nonconventional phosphorus-based tertiary amine curing agent enabling the high fire safety, outstanding tensile strength and high glass transition temperature of epoxy resin

Optimizing transition temperatures for thermochromic smart windows via neural networks coupling simulation

Optimizing transition temperatures for thermochromic smart windows via neural networks coupling simulation

Effects of film thickness on the superconductivity of LaSi2(00l)/Si(100) films

Effects of film thickness on the superconductivity of LaSi2(00l)/Si(100) films

Aramid nanofibers at ultralow loadings: driving significant multifunctionality in epoxy composite dielectrics

Epoxy dielectrics with superior insulation, mechanical, and thermal performance are of great interest for electrical equipment and power electronics. However, integrating these excellent advantages into epoxy presents a formidable challenge. Herein, we detail a simple yet effective strategy for the concurrent enhancement of the dielectric breakdown strength, mechanical toughness, mechanical strength, and the glass transition temperature (Tg) of the epoxy dielectrics by incorporation of a minimal amount of aramid nanofibers (ANFs). It is revealed that a robust interfacial interaction is established between epoxy matrix and the high aspect ratio of ANFs as corroborated by both molecular dynamics simulations and dielectric relaxation spectroscopy. The strong interaction facilitates an optimized interface that enables efficient transfer of interfacial stress and energy dissipation, in turn conferring the ANFs/Epoxy with exceptional mechanical strength (up to 75.68 MPa) and toughness (195 MJ/m3) as well as high Tg (155 °C), respectively. Furthermore, the incorporation of ANFs introduces a multitude of deep traps which effectively impede the migration of charge carriers, contributing to a substantial improvement of the dielectric breakdown strength (196.8 kV/mm) of the ANFs/Epoxy composite, which is almost 4.1 times higher than that of epoxy.

Physicochemical, structural properties, and in vitro digestibility of starches isolated from Amorphophallus konjac K. Koch and Amorphophallus dunnii: A comparison study.

This study compared the physicochemical and structural properties, and in vitro digestibility of Amorphophallus konjac K. Koch starch (AKS) and Amorphophallus dunnii starch (ADS), by using potato starch (PS) as a control. ADS exhibited larger granule sizes, which led to higher transparency, swelling power (SP), and water solubility than AKS. Both AKS and ADS exhibited A-type crystalline patterns; however, ADS demonstrated higher relative crystallinity, gelatinization transition temperatures, and enthalpies of gelatinization, which may be due to higher 1047/1022 and more double helix contents. Regarding rheological and pasting properties, ADS exhibited greater viscosity than that of AKS, likely due to larger particle size and higher SP. In vitro digestion analysis revealed that >50% of each starch type consisted of rapidly digestible starch. Notably, ADS contained the highest amount of resistant starch among the three types. The estimated glycemic index (eGI) values of AKS and ADS were 65.54±0.54 and 63.28±0.36, respectively, indicating that both starch types belong to the medium GI food category, though AKS was significantly higher than ADS. These findings suggest that konjac starch serves as a beneficial dietary carbohydrate alternative. AKS may be suited for fast-digesting food formulas for individuals with digestive impairment, whereas ADS could be advantageous for those managing diabetes.

Tantalum-lanthanum mixing effect on structural and mechanical properties of aluminate glasses

Tantalum-lanthanum mixing effect on structural and mechanical properties of aluminate glasses

Theoretical framework and experimental validation for monitoring the glass transition temperature of thermosets using a low-cost Fresnel reflection sensor

Theoretical framework and experimental validation for monitoring the glass transition temperature of thermosets using a low-cost Fresnel reflection sensor

A simple criterion to exclude the risk of brittle fracture in the brittle-to-ductile transition temperature range

A simple criterion to exclude the risk of brittle fracture in the brittle-to-ductile transition temperature range

Thermally stable PSA film with reduced adhesion after thermal and UV treatment

Thermally stable PSA film with reduced adhesion after thermal and UV treatment

Thermosensitive, injectable, antibacterial glabridin liposome/chitosan dual network hydrogel for diabetic wound healing.

Thermosensitive hydrogels show great potential in healing diabetic wounds, but they are still challenged by the long healing time, risk of infectivity, and accumulation of melanin. Herein, a dual network hydrogel is designed, which consists of chlorogenic acid (CA) modified chitosan (CS) (CA@CS), poly(N-isopropylacrylamide) (PNIPAm), and glabridin liposomes (GL). The gelation transition temperature of the hydrogel is 32-34°C, which thus endows it with superior injectability at ambient temperature. Moreover, GL/PNIPAm/CA@CS also exhibits excellent biocompatibility, and can promote the growth of epidermal cells, and the healing of diabetic wounds. GL/PNIPAm/CA@CS can also control the immune reactions by enhancing the release of CD206, and decreasing the formation of CD86 and ROS, which further promotes the production of CD31 and VEGF, and reduces the expression of pro-inflammatory factors, thus aiding in the healing of diabetic wounds. Furthermore, GL/PNIPAm/CA@CS can also suppress the growth bacterial, which can thus decrease the wound microbiota levels and facilitate the recovery of diabetic wounds. More importantly, it can reduce melanin production by 80% due to the action of glabridin. Consequently, GL/PNIPAm/CA@CS shows significant promise in enhancing the wound healing in future and decreasing the accumulation of melanin.

Polyacrylic acid-based Low Transition Temperature Mixtures (LTTMs) for the exhaustive depolymerization of polyethylene terephthalate (PET)

Polyacrylic acid-based Low Transition Temperature Mixtures (LTTMs) for the exhaustive depolymerization of polyethylene terephthalate (PET)

Tuning the magnetic properties by partial substitution of Cr in D022-Mn3Ga: A potential material for spin transfer torque applications

This report presents the effect of partial substitution of the Cr atom at the itinerant octahedral site (Y2b site) of D022-type Mn3Ga. The Cr introduces a reduction of magnetization due to the antiparallel alignment of Cr atoms at the itinerant site to Mn atoms at the localized site (X4d) with variation in mixed valence states (Mn4+ and Mn3+) from that of the pristine as revealed from the deconvolution of the Mn2p peak. The alloy possesses irreversible magneto-structural phase transformation during heating and cooling modes of temperature-dependent magnetization study. During heating, the magnetic interaction between Mn and Cr atoms possesses an abrupt change in magnetization over temperature, leading to Hopkinson’s like effect with magneto-structural transition temperature (Tc) ∼ 780 K, notably higher than the parent alloy. The thermal variation of uniaxial magnetocrystalline anisotropy ≈1.20-0.2 Merg/cc in addition to high coercivity (∼1.2–2.85 kOe) can be utilized as potential material for spin transfer torque-based memory applications.

Melt electrowriting of amorphous solid dispersions: Influence of drug and plasticizer on rheology and printing performance.

Drug loaded microfiber scaffolds have potential for sublingual or buccal drug delivery due to their fast dissolution time and tunable porosity. Such microfiber scaffolds can be prepared by melt electrowriting (MEW), wherein a polymer melt is electrostatically drawn out of a syringe onto a computer controlled moving collector. The fabrication of such scaffolds via MEW has previously been shown for a polymer with a glass transition temperature (Tg) just above room temperature, making handling challenging. For this reason, ABA triblock copolymers bearing poly(2-oxazoline) and poly(2-oxazine) with slightly higher Tg were synthesized and their processability into drug loaded microfiber scaffolds was assessed. Additionally, plasticizers commonly used in drug products were added to decrease the fabrication temperature. The aim was to investigate the influence of plasticizers on the melt viscosity and printability to expand the polymer platform for the preparation of drug loaded microfiber scaffolds. Temperature dependent melt rheology measurements of the polymers and their mixtures revealed a drop in viscosity by one order of magnitude by the addition of triethyl citrate and ethylene glycol, respectively. Addition of the model drug indomethacin led to a further decrease in viscosity. Even though the drug loaded samples were printable with and without the addition of triethyl citrate, better fiber stacking and therefore improved printing results were obtained with the plasticizer added. However, the addition of the plasticizer did alter the dissolution profile for some of the polymer samples, leading to longer dissolution times or lower drug release compared to the samples without plasticizer, which makes it difficult to predict the influence of the plasticizer on the dissolution profile.