Atomic Chains Research Articles

Tunable magnetism in titanium-based kagome metals by rare-earth engineering and high pressure

Rare-earth engineering is an effective way to introduce and tune magnetism in topological kagome materials, which have been acting as a fertile platform to investigate the quantum interactions between geometry, topology, spin, and correlation. Here, we report the synthesis, structure, and physical properties of titanium-based kagome metals RETi3Bi4 (RE = Yb, Pr, and Nd) with various magnetic states. They all crystallize in the orthogonal space group Fmmm (No. 69), featuring distorted titanium kagome lattices and rare-earth zig-zag chains. By changing the rare earth atoms in the zig-zag chains, the magnetism can be tuned from nonmagnetic YbTi3Bi4 to short-range ordered PrTi3Bi4 (Tanomaly ~ 8.2 K), and finally to ferromagnetic NdTi3Bi4 (Tc ~ 8.5 K). In-situ resistance measurements of NdTi3Bi4 under high pressure further reveal a tunable ferromagnetic ordering temperature. These results highlight RETi3Bi4 as a promising family of kagome metals to explore nontrivial band topology and exotic phases.

Investigating the impact of ultrasound on the structural, physicochemical, and emulsifying characteristics of Dioscorin: Insights from experimental data and molecular dynamics simulation

This study investigated the impact of ultrasound treatment on dioscorin, the primary storage protein found in yam tubers. Three key factors, namely ultrasound power, duration, and frequency, were focused on. The research revealed that ultrasound-induced cavitation effects disrupted non-covalent bonds, resulting in a reduction in α-helix and β-sheet contents, decreased thermal stability, and a decrease in the apparent hydrodynamic diameter (Dh) of dioscorin. Additionally, previously hidden amino acid groups within the molecule became exposed on its surface, resulting in increased surface hydrophobicity (Ho) and zeta-potential. Under specific ultrasound conditions (200 W, 25 kHz, 30 min), Dh decreased while Ho increased, facilitating the adsorption of dioscorin molecules onto the oil-water interface. Molecular dynamics (MD) simulations showed that at lower frequencies and pressures, the structural flexibility of dioscorin's main chain atoms increased, leading to more significant fluctuations between amino acid residues. This transformation improved dioscorin's emulsifying properties and its oil-water interface affinity.

Implementation of the Su-Schrieffer-Heeger Model in the Self-Assembly Si-In Atomic Chains on the Si(553)-Au Surface.

Indium-decorated Si atomic chains on a stepped Si(553)-Au substrate are proposed as an extended Su-Schrieffer-Heeger (SSH) model, revealing topological end states. An appropriate amount of In atoms on the Si(553)-Au surface induce the self-assembly formation of trimer SSH chains, where the chain unit cell comprises one In atom and two Si atoms, confirmed by scanning tunneling microscopy images and density functional calculations. The electronic structure of the system, examined through scanning tunneling spectroscopy, manifests three electron bands within the Si-In chain, accompanied by additional midgap topological states exclusively appearing at the chain's end atoms. To elucidate the emergence of these topological states, a tight-binding model for a finite-length-extended SSH chain is proposed. Analysis of the energy spectra, density of states functions, and eigenfunctions demonstrates the topological nature of these self-assembled atomic chains.

Topologically trivial gap-filling in superconducting Fe(Se,Te) by one-dimensional defects

Structural distortions and imperfections are a crucial aspect of materials science, on the macroscopic scale providing strength, but also enhancing corrosion and reducing electrical and thermal conductivity. At the nanometre scale, multi-atom imperfections, such as atomic chains and crystalline domain walls have conversely been proposed as a route to topological superconductivity, whose most prominent characteristic is the emergence of Majorana Fermions that can be used for error-free quantum computing. Here, we shed more light on the nature of purported domain walls in Fe(Se,Te) that may host 1D dispersing Majorana modes. We show that the displacement shift of the atomic lattice at these line-defects results from sub-surface impurities that warp the topmost layer(s). Using the electric field between the tip and sample, we manage to reposition the sub-surface impurities, directly visualizing the displacement shift and the underlying defect-free lattice. These results, combined with observations of a completely different type of 1D defect where superconductivity remains fully gapped, highlight the topologically trivial nature of 1D defects in Fe(Se,Te).

Benchmarking discrete truncated Wigner approximation and neural network quantum states with the exact dynamics in a Rydberg atomic chain

We benchmark the discrete truncated Wigner approximation (DTWA) and Neural quantum states (NQS) based on restricted Boltzmann-like machines with the exact excitation and correlation dynamics in a chain of ten Rydberg atoms. The initial state is where all atoms are in their electronic ground state. We characterize the excitation dynamics using the maximum and time-averaged number of Rydberg excitations. DTWA results are different from the exact dynamics for large Rydberg-Rydberg interactions. In contrast, by increasing the number of hidden spins, the NQS can be improved but still limited to short-time dynamics. Interestingly, irrespective of interaction strengths, the time-averaged number of excitations obtained using NQS is in excellent agreement with the exact results. Concerning the calculation of quantum correlations, for instance, second-order bipartite and average two-site Rényi entropies, NQS looks more promising. Finally, we discuss the existence of a power law scaling for the initial growth of average two-site Rényi entropy.

Exploring the Odd–Even Effect, Current Stabilization, and Negative Differential Resistance in Carbon-Chain-Based Molecular Devices

The transport properties of molecular devices based on carbon chains are systematically investigated using a combination of non-equilibrium Green’s function (NEGF) and density functional theory (DFT) first-principle methods. In single-carbon-chain molecular devices, a distinct even–odd behavior of the current emerges, primarily influenced by the density of states (DOS) within the chain channel. Additionally, linear, monotonic currents exhibit Ohmic contact characteristics. In ladder-shaped carbon-chain molecular devices, a notable current stabilization behavior is observed, suggesting their potential utility as current stabilizers within circuits. We provide a comprehensive analysis of the transport properties of molecular devices featuring ladder-shaped carbon chains connecting benzene-ring molecules. The occurrence of negative differential resistance (NDR) in the low-bias voltage region is noted, with the possibility of manipulation by adjusting the position of the benzene-ring molecule. These findings offer a novel perspective on the potential applications of atom chains.

Chains of atoms embedded into transition metal dichalcogenides as one-dimensional half-metallic magnets

Chains of atoms embedded into transition metal dichalcogenides as one-dimensional half-metallic magnets

Expanding the CHARMM36 United Atom Chain Model for the Inclusion of Sphingolipids.

The inclusion of accurate yet computationally inexpensive lipid force fields (FF) is pertinent for the study of lipids and lipid-containing systems using molecular dynamics (MD). Within the past decade, the implementation and further expansion of a united atom (UA) FF for lipids have been developed in the CHARMM family of FFs. The most recent version of the UA presented more accurate descriptions of lipid properties for several phospholipids with saturated and monounsaturated chains, termed C36UAr. However, the original C36UAr model lacks parameters for an important class of lipids, such as sphingolipids. The focus of this article is to broaden the scope of the C36UAr chain model to incorporate these lipids. In this study, two common sphingolipids, N-palmitoyl sphingomyelin and N-stearoyl sphingomyelin are converted to a UA-chain representation and simulated to investigate the accuracy and speed over the all-atom FF model for sphingolipids. Improvements were found among multiple parameters, for example, in the surface area per lipid (SA/lip) and hydrogen order parameters, over the all-atom simulations of these sphingomyelins in C36, while as much as halving the simulation time for simulations of the same setup otherwise. Thus, the accuracy and efficiency found in this study are consistent with those found in the C36UAr model for phospholipids and expand the application of C36UAr to a wider array of membrane models to better match that in vivo.

Thermo-mechanical behaviours investigation of Nano-Sized Al2O3, TiO2, and Graphene Nanoplatelet Reinforced Epoxy Composites

Composite materials find extensive applications in various industries, thanks to their remarkable properties. These sectors include energy, maritime, motor sports, aviation, space and defense. The materials commonly used in these sectors are fiber reinforced plastic (FRP) composite materials. Epoxy materials are commonly used as matrix in the production of FRP materials. This study delves into the enhancement of epoxy-based nanocomposites by using graphene nanoplatelets (GNP-5nm), TiO2 (13nm), and Al2O3 (8nm) nanoparticles. These nanoparticles were added at varying mass ratios into a commercial epoxy to investigate their effects on some chemical, thermal and mechanical properties. Meticulous mixing methodologies were used to reduce clumping effects and ensure even distribution during the process. The curing process was carried out in a PLC (Programmable Logic Controller) controlled hot air oven under isothermal conditions under the influence of 100 °C for 30 minutes. Tensile strength, elongation at break, toughness, resilience modulus, elasticity modulus, hardness, FTIR analysis and thermal conductivity properties were characterized to assess the nanoparticle influence on the epoxy matrix. The results showed that there were remarkable improvements in mechanical properties with nanoparticle reinforcement. Especially, 1.25% Al2O3 inclusion exhibited a substantial increase of 140.32% in tensile strength and a 7% rise in shore D hardness compared to pure epoxy. This enhancement was attributed to enhanced O-H bonding between 'O' atoms in Al2O3 nanoparticles and epoxy polymer chains, enhancing matrix-filler interactions. Additionally, the effect of 1.0% TiO2 led to plasticity, displaying a 32% rise in elongation at break, signifying improved deformation energy absorption compared to neat epoxy. In thermal conductivity measurements, the highest thermal conductivity was observed in the sample with 1.25% GNP added and it increased by 123.5% compared to neat epoxy. In TiO2 and Al2O3 added samples, an increase of 69% and 47%, respectively, was observed at 1.25% additive rates compared to neat epoxy. According to the results, thanks to the nanoparticle reinforcement added into the epoxy matrix, composite structures can be given new and superior properties specific to the applications.

Modulating thermal and electrical conductivities in polymers: An approach toward extracting molecular design rules through atomistic simulations

Polymers are extensively employed in diverse industries, including electrical equipment and electronic devices. Recent technological advancements have intensified the demand for dielectric polymers with both high insulation resistance and high thermal conductivity. We employed molecular dynamics simulations to clarify the intricate relationship between molecular structures, thermal conductivity, and ionic mobility from an atomistic point of view. Examined polymers include polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, polyoxymethylene, and polyethylene oxide. Based on the elucidated correlations among force field parameters, we found that the parameters can be clustered into four groups: group 1 (atomic and bond parameters and force constant of the bond angle), group 2 (equilibrium angle and force constant of dihedral angle), and group 3 (side chain atom charges). Thermal conductivity showed relationships with parameters in group 1, with correlation coefficients mostly exceeding 0.7 in the absolute value. Considering the correlations between the parameters, we systematically altered the parameters within each group and computed thermal conductivity and ionic mobility. When altering the force field parameters of groups 1 and group 2, a trade-off relationship between thermal conductivity and ionic mobility becomes evident. Conversely, altering the force field parameters in group 3 increased thermal conductivity while decreasing ionic mobility, breaking the trade-off relationship. The proposed clustered-parameter variation method can predict the changes in the electrical and thermal conductivity of polymers through molecular structure modifications. The method, being a general and first-principles approach, is likely to have significant advantages in the molecular design across a diverse range of polymers.

Quantum teleportation in Heisenberg chain with magnetic-field gradient under intrinsic decoherence

One of the most appealing quantum communication protocols is quantum teleportation, which involves sharing entanglement between the sender and receiver of the quantum state. We address the two-qubit quantum teleportation based on the Heisenberg XYZ chain with a magnetic-field gradient affected by intrinsic decoherence. An atomic spin chain is primarily coupled to the linear gradient of the magnetic field in the x-direction, with the assumption that the magnetic field varies linearly with the position of the atom. By using the concepts of fidelity and average fidelity in the presence of the magnetic field gradient and under the effect of intrinsic decoherence in the current model, and considering the variables of the system, an improved quantum teleportation can be achieved. In addition, using the concept of remote quantum estimation, we examine remote quantum sensing in this article, which is very useful in quantum communication.

Static vector solitons in a topological mechanical lattice

Topological solitons, renowned for their stability and particle-like collision behaviors, have sparked interest in developing macroscopic-scale information processing devices. However, the exploration of interactions between multiple topological solitons in mechanical systems remains elusive. In this study, we construct a topological mechanical lattice supporting static vector solitons that represent quantized degrees of freedom and can freely propagate across the system. Drawing inspiration from coupled double atomic chains with sublattice symmetry breaking, we design a mechanical analogue featuring topologically protected boundary modes and induce independent modes to finite motions along branched motion pathways. Through a continuum theory, we describe the evolution of boundary modes with vector solitons composed of superposed kink solutions, identifying them as minimum energy pathways on the rugged effective potential surface with multiple degenerate ground states. Our results reveal the connection between transformable topological lattices and multistable systems, providing insight into nonlinear topological mechanics.

Poly (aniline-co-aniline-2,5-disulfonic acid) / L-ascorbic acid / Ag@SiO2 / polysafranin nanocomposite: synthesis, characterization and anomalous electrical behaviour.

We report the synthesis of sulfonated copolyaniline/polysafranin/L-ascorbic acid/Ag@SiO2 fine powdered nanocomposites and investigate the influence of incorporating the dye on their conductivity. The composite was characterized via IR, UV, cyclic voltammetry (CV), electric, dielectric, SEM, TEM, TGA and DSC measurements. Microscopy images revealed intensified spherical particles that were dispersed across the entire surface, and the SiO2/Ag particles were distributed on the surface. The XRD results exhibited peaks at many 2q values, and their interatomic spacing (d) and crystallite (grain) sizes were calculated. The thermal degradation curves exhibited an interesting model of stability. The cyclic voltammogram exhibited redox peaks identical to those of the reported analogues. The d.c. conductivity of the oligomer varied from 0.06 - 0.016 (s/cm), and that of the composite varied from 0.008 to 0.016 (s/cm). The material changed from a semiconductor to a metallic material. The observed conductivity is mainly attributed to self-doping between the sulfonate groups and the charged nitrogen atoms in the polymer chains. The frequency dependence of the permittivity, ε', showed a marked effect on the frequency window under consideration. The permittivity, ε', is independent of the increase in the frequency of the oligomer and the composite. This behavior supports the non-Debye dependency by confirming the occurrence of electrode polarization and space charge effects. In conclusion, the incorporation of safranin dye with a thermally stable, highly sulfonated polyaniline derivative/Ag@SO2 nanocomposite achieved improved conductivity after heating. The d.c. conductivities are comparable to those of many commercial inorganic or organic composites, and because of their attractive electrical properties, we suggest that these materials are promising for electronic field applications.

Solution NMR chemical shift assignment of apo and molybdate-bound ModA at two pHs.

ModA is a soluble periplasmic molybdate-binding protein found in most gram-negative bacteria. It is part of the ABC transporter complex ModABC that moves molybdenum into the cytoplasm, to be used by enzymes that carry out various redox reactions. Since there is no clear analog for ModA in humans, this protein could be a good target for antibacterial drug design. Backbone 1H, 13C and 15N chemical shifts of apo and molybdate-bound ModA from E. coli were assigned at pHs 6.0 and 4.5. In addition, side chain atoms were assigned for apo ModA at pH 6.0. When comparing apo and molybdate-bound ModA at pH 6.0, large chemical shift perturbations are observed, not only in areas near the bound metal, but also in regions that are distant from the metal-binding site. Given the significant conformational change between apo and holo ModA, we might expect the large chemical shift changes to be more widespread; however, since they are limited to specific regions, the residues with large perturbations may reveal allosteric sites that could ultimately be important for the design of antibiotics that target ModA.

Vibrational properties of disordered stealthy hyperuniform 1D atomic chains

Disorder hyperuniformity is a recently discovered exotic state of many-body systems that possess a hidden order in between that of a perfect crystal and a completely disordered system. Recently, this novel disordered state has been observed in a number of quantum materials including amorphous 2D graphene and silica, which are endowed with unexpected electronic transport properties. Here, we numerically investigate 1D atomic chain models, including perfect crystalline, disordered stealthy hyperuniform (SHU) as well as randomly perturbed atom packing configurations to obtain a quantitative understanding of how the unique SHU disorder affects the vibrational properties of these low-dimensional materials. We find that the disordered SHU chains possess lower cohesive energies compared to the randomly perturbed chains, implying their potential reliability in experiments. Our inverse partition ratio (IPR) calculations indicate that the SHU chains can support fully delocalized states just like perfect crystalline chains over a wide range of frequencies, i.e. ω∈(0,100) cm−1, suggesting superior phonon transport behaviors within these frequencies, which was traditionally considered impossible in disordered systems. Interestingly, we observe the emergence of a group of highly localized states associated with ω∼200 cm−1, which is characterized by a significant peak in the IPR and a peak in phonon density of states at the corresponding frequency, and is potentially useful for decoupling electron and phonon degrees of freedom. These unique properties of disordered SHU chains have implications in the design and engineering of novel quantum materials for thermal and phononic applications.

Anisotropic metal–insulator transition in strained VO2(B) single crystal

Mechanical strain can induce noteworthy structural and electronic changes in vanadium dioxide, imparting substantial scientific importance to both the exploration of phase transitions and the development of potential technological applications. Unlike the traditional rutile (R) phase, bronze-phase vanadium dioxide [VO2(B)] exhibits an in-plane anisotropic structure. When subjected to stretching along distinct crystallographic axes, VO2(B) may further manifest the axial dependence in lattice–electron interactions, which is beneficial for gaining insights into the anisotropy of electronic transport. Here, we report an anisotropic room-temperature metal–insulator transition in single-crystal VO2(B) by applying in-situ uniaxial tensile strain. This material exhibits significantly different electromechanical responses along two anisotropic axes. We reveal that such an anisotropic electromechanical response mainly arises from the preferential arrangement of a strain-induced unidirectional stripe state in the conductive channel. This insulating stripe state could be attributed to the in-plane dimerization within the distorted zigzag chains of vanadium atoms, evidenced by strain-modulated Raman spectra. Our work may open up a promising avenue for exploiting the anisotropy of metal–insulator transition in vanadium dioxide for potential technological applications.

Regioisomeric functionalization of azo-bridged nitropyrazoles: Pushing the density limit of catenated nitrogen systems

Fully energetic functionalization of catenated nitrogen systems is highly challenging due to the lack of incorporation methodology. In this work, two catenated nitrogen N6 structures containing six nitro groups, i.e., (E)-1,1′-bis [5-Nitroamide-3,4-dinitro-1H-pyrazole] diazene (N-N6A) and its regioisomer (E)-1,1′-bis [4-Nitroamide-3,5-dinitro-1H-pyrazole] diazene(N-N6B) were designed and synthesized. Despite the same chemical formula and azo functionality, N-N6B exhibits better overall performance than N-N6A. Meanwhile, N-N6B has the highest density with excellent detonation performance (d = 1.94 g cm−3, Dv = 9440 m s−1, and P = 39.6 GPa) among the reported long-catenated nitrogen atom chains, indicating the potential for high energy materials. Particularly, as the precursors of N-N6A and N-N6B, the mechanical sensitivities of N6A and N6B (N6A, IS = 11 J, FS = 160 N; N6B, IS = 14 J, FS = 240 N) are apparently superior to that of literature long nitrogen-chains energetic material. The different performance of these compounds highlights the effect of the regioisomeric functionalization on designing advanced energetic materials.

Metal-organic framework-templated ZnIn2S4 nanomaterials for high-performance photocatalytic H2‐evolution

ZIF-8-templated ZnIn2S4 (ZIS) crystals with different morphologies have been synthesized solvothermally by varying the organic solvents, while thioacetamide (TAA) and L-cysteine (L‐cyst) were used as sulfur precursors. It is found that solvothermal properties, including ions coordination, dielectric constant, and atomic chain length, influence the nucleation and growth of ZIS composites. The differences in morphology and composition of the prepared ZIS crystals strongly affect their photophysical properties and photocatalytic hydrogen evolution reactions (PHER). The hydrogen evolution rates for ZIS composites decrease in the following order: Leaf‐like (EG, TAA) > nanorods (EtOH, TAA) > nanoflowers (EG, L‐cyst) > nanosheets (Gly, TAA) > irregular particles (EDA, TAA) > plate‐like (DETA, TAA). The leaf‐like ZIS‐EG composite prepared using TAA as a sulfur precursor and ethylene glycol (EG) as a solvent shows an excellent PHER performance of 5208 μmol g−1 h−1 (44.91 μmol) with an apparent quantum yield (AQY) of 4.80% at 420 nm. The ZIS‐EG composites with different ZIF‐8 contents (50, 100, 150, and 200 mg) were also investigated for the PHER activity with mixed Na2S/Na2SO3 sacrificial agent at λ ≥ 420 nm. It shows that the nature of solvents and sulfur precursors had a significant influence on the morphology, photoabsorption, electrochemical properties, and PHER performance of ZIF‐8‐templated ZIS composites, which complements the knowledge of designing efficient and perspective photocatalysts with enhanced visible‐light‐driven PHER performance.

Understanding the effect of foreign atoms occupation on the metamagnetic behaviors in MnCoSi-based alloys: taking Pt-doping as an example

Present research on TiNiSi-type MnCoSi-based alloys focuses on finding a suitable doping element to effectively reduce the critical magnetic field (μ 0 H cri) required to induce a metamagnetic transition. This paper provides a guide to achieve this goal through an experimental investigation of Mn1−x Pt x CoSi and MnCo1−x Pt x Si alloys. In Mn1−x Pt x CoSi, as x increases, μ 0 H cri at room temperature decreases, while in MnCo1−x Pt x Si, it increases. This phenomenon can be attributed to the fact that larger Pt atoms prefer Co sites over Mn sites, as predicted by our density-functional theory. Consequently, in Mn1−x Pt x CoSi, larger Co atoms are extruded into the Mn atoms chain, increasing the nearest Mn–Mn distance and resulting in a reduced μ 0 H cri. This finding suggests that transition-metal atoms with more valence electrons preferably occupy the Co site, while those with fewer valence electrons preferably occupy the Mn site. Adhering to this rule, one can easily obtain a low μ 0 H cri and large magnetostrain under a low magnetic field by selecting a suitable foreign element and chemical formula, as demonstrated by the Mn1−x Pt x CoSi alloy.

Quantitative analysis method for absorption mechanism and energy consumption of CO2 capture by amino acid ionic liquids

Amino acid ionic liquids (AAILs) are attractive candidates for CO2 capture due to their high solubility for CO2. Quantitatively analyzing the interaction of amino groups in AAILs with CO2 and evaluating the energy consumption of CO2 capture is critical to the molecular design of ideal AAILs. In this work, a thermodynamic model based on the cubic plus association equation of state was proposed to calculate the contribution from the chemical reactions between various stoichiometric ratios of CO2 and AAIL (Nm:n,m:n is stoichiometric ratio) on CO2 solubility. The results show that the larger contribution to the CO2 solubility in [Glu], [Tyr] and [Gln]-IL with strong polar groups is derived from association scheme N1:2, while the N1:1 association interaction is the dominant contribution of [Gly], [Ala], [Val] and [Pro]-IL with hydrogen atom or short alkyl side chains, and [VBIm]-IL with multiple amino groups. The N2:1 association interaction is primary between CO2 and [Cho][His] or [Cho][Arg]. Besides, the contributions of these association effects are greater than that of dispersion and repulsion to CO2 solubility. Then, the solvent cyclic capacity and regeneration energy of AAILs in the pressure swing and temperature swing CO2 capture system were estimated. More amino groups result in higher regeneration energy consumption and do not necessarily increase solvent cyclic capacity. Among the studied AAILs, [Cho][Gly] which exhibits high cyclic capacity and low energy consumption has great potential in CO2 capture solvent.