Structural Symmetry Research Articles

Daily and annual modulation rate of low mass dark matter in silicon detectors

Low-threshold solid-state detectors with single electron excitation sensitivity can probe nuclear recoil energies in the sub-100 eV range, coinciding with the typical threshold displacement energies in the detector material. We investigate the daily and annual modulation of the observable event rate for dark matter mass ranging from 0.2 to 5 GeV/c2 in a silicon detector, considering the energy threshold and the direction of the nuclear recoil. The data for the energy threshold is obtained from a molecular dynamics simulation. It is shown that the directional dependence of the threshold energy and the motion of the laboratory result in the modulation of the interaction event rate. We demonstrate silicon’s average annual interaction rate is more considerable than germanium for low-mass dark matter. However, their event rates take a similar trend in large dark matter masses. Thus, silicon can be a reliable target to discriminate low-mass dark matter from backgrounds. We also find 8 h and 12h periodicities in the time series of event rates for silicon detectors due to the 45-degree symmetry in the silicon crystal structure.

Effects of KoBo-Processing and Subsequent Annealing Treatment on Grain Boundary Network and Texture Development in Laser Powder Bed Fusion (LPBF) AlSi10Mg Alloy

It is well known that the properties of polycrystalline metals are related to grain boundaries (GBs), which are fundamental structural elements where crystallographic orientations change abruptly and often exhibit some degree of symmetry. Grain boundaries often exhibit unique structural, chemical, and electronic properties that differ from bulk crystalline domains. Their effects on material properties, including mechanical strength, corrosion resistance, and electrical conductivity, make grain boundaries a focus of intense scientific investigation. In this study, the microstructural transformation of an AlSi10Mg alloy subjected to KoBo extrusion and subsequent annealing is investigated. A notable discovery is the effectiveness of a strain-annealing method for grain boundary engineering (GBE) of the LPBF AlSi10Mg alloy. In particular, this study shows a significant increase in the population of coincidence site lattice boundaries (CSL), which embody the symmetry of the crystal lattice structure. These boundaries, which are characterised by a high degree of symmetry, contribute to their special properties compared to random grain boundaries. The experimental results emphasise the crucial role of strain-induced boundary migration (SIBM) in the development of a brass texture in the microstructure of the alloy after annealing. In addition, the presented results demonstrate the feasibility of applying GBE to materials with high stacking fault energy (SFE), which opens up new possibilities for optimizing their properties.

A layered perovskite La2Ni1-xSbxO4+δ-molten carbonate dual-phase membrane for CO2 separation

A new series of layered perovskite K2NiF4 structure La2Ni1-xSbxO4+δ (LNSx, x = 0, 0.025, 0.05) were used to prepare the LNSx-molten carbonate (MC) dual-phase membrane for CO2 separation. Sb doping at the Ni site is expected to enhance CO2 permeability and improve the resistance towards CO2/carbonate corrosion. In this work, the CO2 permeability of the LNSx- MC membrane was investigated for CO2-containing atmospheres with and without oxygen, and correlated with the lattice characteristics, microstructure, chemical bond, and conductivity of LNSx support. The result shows that the introduction of Sb improves the structure symmetry and increases the interstitial oxygen concentration, which is beneficial for oxygen ion transport. The superior CO2 permeability of Sb-doped sample is confirmed by the higher permeation fluxes with value of 0.15 mL min−1 cm−2 at 800 °C of LNS0.025-MC dual-phase membrane in 50% CO2 + 50% N2. In addition, the LNS0.025-MC dual-phase membrane achieves a great enhancement in chemical and structural stability compared to the LNS0. In the simulated flue gas 15% CO2 + 10% O2 + 75% N2, the LNS0.05-based dual phase membrane shows a high permeation flux of 1.07 mL min−1 cm−2 at 800 °C, which is 2 times higher than that of LNS0-based dual-phase membrane.

Long-lived valley states in bilayer graphene quantum dots

Bilayer graphene is a promising platform for electrically controllable qubits in a two-dimensional material. Of particular interest is the ability to encode quantum information in the valley degree of freedom, a two-fold orbital degeneracy that arises from the symmetry of the hexagonal crystal structure. The use of valleys could be advantageous, as known spin- and orbital-mixing mechanisms are unlikely to be at work for valleys, promising more robust qubits. The Berry curvature associated with valley states allows for electrical control of their energies, suggesting routes for coherent qubit manipulation. However, the relaxation time of valley states—which ultimately limits these qubits’ coherence properties and therefore their suitability as practical qubits—is not yet known. Here we measure the characteristic relaxation times of these spin and valley states in gate-defined bilayer graphene quantum dot devices. Different valley states can be distinguished from each other with a fidelity of over 99%. The relaxation time between valley triplets and singlets exceeds 500 ms and is more than one order of magnitude longer than for spin states. This work facilitates future measurements on valley-qubit coherence, demonstrating bilayer graphene as a practical platform hosting electrically controlled, long-lived valley qubits.

Generalized Sum-Asymmetry Model and Orthogonality of Test Statistic for Square Contingency Tables

For analyzing contingency tables, we are usually interested in whether or not the independence model holds. On the other hand, for the analysis of square contingency tables, we are usually interested in whether or not the model having the structure of symmetry or asymmetry with respect to the main diagonals cells holds. This study proposes a generalized sum-asymmetry model including the exponential and relative exponential sum-symmetry models. This generalized model indicates that the cumulative probability that the sum of classes for row and column variables is s within the upper right cell of the table, is exponentially higher than the cumulative probability that the sum of classes for row and column variables is s within the lower left cell. Additionally, this study gives a separation of the sum-symmetry model using the proposed model, and reveals that the new separation satisfies the asymptotic equivalence for the test statistic. The utilities of the proposed methods are demonstrated through the real data analysis.

Tailoring energy barriers of Bloch-point-mediated transitions between topological spin textures

Magnetic skyrmions are nanoscale spin textures whose thermal stability originates from the nontrivial topology in nature. Recently, a plethora of topological spin textures have been theoretically predicted or experimentally observed, enriching the diversity of the skyrmionic family. In this work, we theoretically demonstrate the stabilities of various topological spin textures against homochiral states in chiral magnets, including chiral bobbers, dipole strings, and skyrmion tubes. They can be effectively classified by the associated topological Hall signals. Multiple transition paths are found among these textures, mediated by Bloch-point singularities, and the topological protection property here can be manifested by a finite energy barrier with the saddle point corresponding to the Bloch-point creation/destruction. By carefully modulating the local property of a surface, such as interfacial Dzyaloshinskii-Moriya interaction induced by breaking the structural symmetry, the energy landscape of a magnetic system can be tailored decisively. Significantly, the proposed scenario also enables the manipulation of stabilities and transition barriers of these textures, even accompanied by the discovery of ground-state chiral bobbers. This study may raise great expectations on the coexistence of topological spin textures as spintronics-based information carriers for future applications. Published by the American Physical Society 2024

Chemical‐Stabilized Aldehyde‐Tuned Hydrogen‐Bonded Organic Frameworks for Long‐Cycle and High‐Rate Sodium‐Ion Organic Batteries

AbstractHydrogen‐bonded organic frameworks (HOFs) are considered as potential choice for future energy storage systems due to their adjustable chemistry, environment friendliness, and cost‐effectiveness. In this study, structurally stabilized and aldehyde‐tuned hydrogen‐bonded organic frameworks (HOFs‐8) are designed and prepared to contain arrayed electronegative sites for sodium‐ion storage. Benefitting from the flexible hydrogen bond and unique structural symmetry, HOFs‐8 can achieve efficient utilization of the active sites and fast transport of sodium ions and electrons. The HOFs‐8 electrode exhibits an impressive lifespan of 5000 cycles at 3.66 A g−1 (20 C). In situ Fourier Transform infrared spectroscopy (in situ FT‐IR) and ex situ X‐ray Photoelectron Spectroscopy (ex situ XPS) analyses are performed to illustrate the mechanism of sodium‐ion storage involving aldehyde‐tuned C═O. Additionally, flexible hydrogen bonds in HOFs materials with unique structural symmetries are investigated to elucidate the mechanism of hydrogen bonding for improving their electrochemical properties. Density functional theory (DFT) simulations verified that HOFs‐8 has excellent Na+ diffusion kinetics, enabling it to demonstrate outstanding rate capability. This work offers insight into the design of new electrodes and improved HOFs, which are expected to have tremendous potential in energy storage systems.

Giant intrinsic photovoltaic effect in one-dimensional van der Waals grain boundaries

The photovoltaic effect lies at the heart of eco-friendly energy harvesting. However, the conversion efficiency of traditional photovoltaic effect utilizing the built-in electric effect in p-n junctions is restricted by the Shockley-Queisser limit. Alternatively, intrinsic/bulk photovoltaic effect (IPVE/BPVE), a second-order nonlinear optoelectronic effect arising from the broken inversion symmetry of crystalline structure, can overcome this theoretical limit. Here, we uncover giant and robust IPVE in one-dimensional (1D) van der Waals (vdW) grain boundaries (GBs) in a layered semiconductor, ReS2. The IPVE-induced photocurrent densities in vdW GBs are among the highest reported values compared with all kinds of material platforms. Furthermore, the IPVE-induced photocurrent is gate-tunable with a polarization-independent component along the GBs, which is preferred for energy harvesting. The observed IPVE in vdW GBs demonstrates a promising mechanism for emerging optoelectronics applications.

Rigorous coupled-wave analysis of unilateral Smith-Purcell radiation from asymmetric resonators.

The Smith-Purcell radiation produced by electrons moving closely to a grating can be enhanced by resonances. Here, we show a method to manipulate the directionality of the resonance-enhanced radiation. Using the rigorous coupled-wave analysis method, we compare the radiation from symmetric and asymmetric gratings, showing that the enhanced Smith-Purcell radiation can become unilateral with a perturbation that breaks the structural symmetry. Our work provides an effective method for frequency-domain calculation of Smith-Purcell radiation and also an approach to realize more efficient use of the radiation.

Arbitrary Virtual Try-on Network: Characteristics Preservation and Tradeoff between Body and Clothing

Deep learning based virtual try-on system has achieved some encouraging progress recently, but there still remain several big challenges that need to be solved, such as trying on arbitrary clothes of all types, trying on the clothes from one category to another and generating image-realistic results with few artifacts. To handle this issue, we in this article first collect a new dataset with all types of clothes, i.e., tops, bottoms, and whole clothes, each one has multiple categories with rich information of clothing characteristics such as patterns, logos, and other details. Based on this dataset, we then propose the Arbitrary Virtual Try-On Network (AVTON) that is utilized for all-type clothes, which can synthesize realistic try-on images by preserving and trading off characteristics of the target clothes and the reference person. Our approach includes three modules: (1) Limbs Prediction Module, which is utilized for predicting the human body parts by preserving the characteristics of the reference person. This is especially good for handling cross-category try-on task (e.g., long sleeves ↔ short sleeves or long pants ↔ skirts), where the exposed arms or legs with the skin colors and details can be reasonably predicted; (2) Improved Geometric Matching Module, which is designed to warp clothes according to the geometry of the target person. We improve the TPS based warping method with a compactly supported radial function (Wendland’s Ψ-function); (3) Trade-Off Fusion Module, which is to tradeoff the characteristics of the warped clothes and the reference person. This module is to make the generated try-on images look more natural and realistic based on a fine-tune symmetry of the network structure. Extensive simulations are conducted and our approach can achieve better performance compared with the state-of-the-art virtual try-on methods.

Realization of future neuro-biological architecture in power efficient memristors of Fe3O4/WS2 hybrid nanocomposites

The future generation of digital technology will heavily rely on power efficient non-volatile resistive memory systems as a potential alternative to flash memory due to its limitations in scalability and endurance. To attain the commercial benchmark, memristors have still lacked performance. This study reports a novel and cost-effective solution processable method for growing surface-modified hybrid nanocomposites (Nc) on a large scale, as an active layer. The solution-processed synthesis approach used for Ag/Fe50W50/Pt hybrid nanocomposite memristor device results in the formation of heterophase grain boundaries, which create residual filaments along these boundaries. The device Fe3O4-WS2(Nc) shows excellent performance, having ultra-low energy consumption (0.1fJ), high reproducibility (10 devices), scalability, excellent endurance (106), and excellent environment stability. Density functional theory (DFT) simulations reveal that structural symmetry distortion and interfacial interaction of hybrid nanocomposite at the interface plays a vital role in the switching mechanism. As high-performance electronic synapses, the optimal pulse scheme enables a steady interaction of short- and long-term plasticity principles, such as spike -time dependent plasticity (STDP) and pulse pair facilitation (PPF), essential for learning and neuromorphic computing analogous to human brain. Moreover, by using Modified National Institute of Standards and Technology (MINST), the memristor device attained a high learning accuracy of 95.4% under convolution neural network (CNN) simulations. The present study revealed that the performance of hybrid-nanocomposite memristors could lead to efficient future neuromorphic architecture.

Polarization independent tunable bandwidth absorber based on single-layer graphene

As the demand for cognitive understanding of the THz band continues to grow, there is significant potential for practical applications in designing optical devices operating in this frequency range. This paper proposes a polarization-independent tunable bandwidth absorber based on a monolayer graphene, capable of achieving an absorption rate higher than 0.9 in the 3–6 THz band. The absorber exhibits polarization incoherence due to the structural symmetry. Analysis of the electric field distribution indicates that the strong absorption effect of the absorber primarily arises from the coupling of localized surface plasmon resonance (LSPR). The absorber also demonstrates excellent tunability, both in terms of physical and chemical properties, while maintaining optimal absorption performance at a 45° incidence angle. This implies that the absorber holds significant potential for applications in fields such as biomedicine and communications.

A novel symmetrically structured protonated ionic liquids for alkane de‐aromatization

AbstractThe efficient separation of aromatics/alkanes is important for the efficient utilization of fossil resources. Based on the influence of ionic symmetry structure on the polarity, melting point, interaction force, and spatial site resistance of ionic liquid solvents, a protonic ionic liquid with anionic and cationic double symmetry structure [DMI][FeCl4] was designed and synthesized for alkane de‐aromatization process, which enhances the Van der Waals forces dominated by dispersed forces with aromatics, and thus enhances the extraction efficiency of aromatic. For the binary system of dodecane/decalin + tetralin/1‐methylnaphthalene, and two simulated oil systems of six‐component straight‐sun diesel fuel and hydrofinishing LCO, [DMI][FeCl4] showed excellent de‐aromatization effects. The selectivity coefficients for monocyclic and bicyclic aromatic hydrocarbons can reach 150 and 480, respectively. When used in the de‐aromatization process of real oils, about 40% of the aromatic hydrocarbons can be removed by a single extraction using a 1:5 O/A ratio.

Tunable quintuple plasmon-induced transparency and the effect of symmetry breaking based on monolayer graphene split rings metasurface

A monolayer graphene metasurface composed of two large graphene split rings (TLGSRs) and two small graphene split rings (TSGSRs) is designed and proposed to achieve a tunable quintuple plasmon-induced transparency (QPIT) by coupled mode theory (CMT) and finite-difference time-domain (FDTD) simulations. We successfully realized and designed quintuple-frequency asynchronous, sextuple-frequency asynchronous, and sextuple-frequency synchronous photoelectric switches by dynamically adjusting the Fermi energy levels of graphene. The switches exhibit remarkable performance characteristics, including amplitude modulation degree (AMD) ranging from 71.0 % to 90.0 % and extinction ratio from 5.37 dB to 9.8 dB. The sensitivity of the proposed metasurface was studied and could reach 474 GHz/RIU. The proposed metasurface exhibits polarization-sensitive features due to its non-central symmetry in the metasurface. Finally, the metasurface symmetry-breaking effect on QPIT is further investigated, and results indicate that triple-PIT, quadruple-PIT, quintuple-PIT, and sextuple-PIT can be mutually transformed and regulated through structural symmetry breaking. In summary, the findings provide valuable guidance for the design of optoelectronic switches, sensors, and modulators.

Tailoring topological nature of merging bound states in the continuum by manipulating structure symmetry of the all-dielectric metasurface

Tailoring topological nature of merging bound states in the continuum by manipulating structure symmetry of the all-dielectric metasurface

Two-fold symmetric superconductivity in the Kagome superconductor RbV3Sb5

The recently discovered kagome superconductors offer a promising platform for investigating intertwined orders and novel states, including topology, superconductivity, charge density waves, and more. The interplay among these orders can spontaneously break rotational symmetry, giving rise to exotic phenomena such as nematicity or even nematic superconductivity. Here we present our findings on the two-fold symmetric superconductivity in thin-flake RbV3Sb5 in response to direction-dependent in-plane magnetic fields, in contrast to the inherent six-fold structural symmetry of the crystal lattice. The two-fold symmetry was evidenced through a combination of magnetoresistance transport experiments, critical magnetic field measurements, and observations of anisotropic superconducting gaps. Additionally, by altering the experimental configuration, we also detected the presence of six-fold symmetric components superimposed on the two-fold symmetry at the boundary between normal and superconducting states. Our results underscore the correlation-driven symmetry-breaking phenomena and emphasize the potential of this correlated kagome family as a promising platform for investigating intertwined orders, including unconventional superconductivity.

Supramolecular assemblies of citalopram and escitalopram in β-cyclodextrin dimeric cavity: Crystallographic and theoretical insights

Cyclodextrin (CD) encapsulation improves physicochemical and pharmacological properties of selective serotonin reuptake inhibitors (SSRIs), which are efficacious in treating depression, a global mental health problem. Here, we scrutinize β-CD inclusion complexes with racemate citalopram (rac-CTP; 1) and escitalopram ((S)-CTP; 2) by combined single-crystal X-ray diffraction and DFT full-geometry optimization. X-ray analysis unveiled that the 2:2 inclusion complexes of 1 and 2 with similar inclusion modes and topologies are stabilized by various intermolecular interactions of host–guest CH···π, host–host OH···O H-bonds, and guest–guest F···F in the tail-to-tail dimeric asymmetric unit. In the crystals, these dimers are stacked on top of each other, yielding similar channel structures of distinct crystal symmetries, triclinic, P1 (1) and monoclinic, P21 (2), which are further maintained by guest–guest π···π and CN···π interactions. The thermodynamic stabilities evaluated by DFT calculation indicate the vital role of weak intermolecular interactions in the formation and stabilization of the β-CD monomeric and dimeric inclusion complexes. This study provides crystallographic and theoretical evidence for the improved stability and the masked bitterness of CTP through β-CD encapsulation as patented previously and suggests the pharmaceutical implications in the drug delivery and enantioseparation.

Computation of Wiener and Wiener Polarity Indices of a Class of Nanostar Dendrimer Using Vertex Weighted Graphs

Nanostar dendrimers are tree-like nanostructures with a well-defined, symmetrical architecture. They are built in a step-by-step, controlled synthesis process, with each layer or generation building on the previous one. Dendrimers are made up of a central core, a series of repeating units or branches, and a surface group shell. A weighted graph is a type of graph in which vertices or edges are assigned weights that represent cost, distance, and a variety of other relative measuring units. The weighted graphs have many applications and properties in a mathematical context. The topological indices are numerical values that represent the symmetry of a molecular structure. They have rich applications in theoretical chemistry. Various topological indices can be used to investigate a wide range of properties of chemical compounds with a molecular structure. They are very important in mathematical chemistry, especially in quantitative structure-activity relationship (QSAR) and quantitative structure-property relationship (QSPR) studies. In this paper, we examine the topological properties of the molecular graphs of nanostar dendrimers. For this purpose, the topological indices, namely, the Wiener index and the Wiener polarity index are computed for a class of nanostar dendrimers.

ISODISTROTLaMTeO6 (M = Ga3+ and Mn3+): the critical role of electronic configuration and cation ordering in crystal structures.

In this work, PbSb2O6-type oxides LaMTeO6 (M = Ga3+ and Mn3+) were synthesized and structurally characterized by Rietveld refinements against high-resolution X-ray powder diffraction data. The Ga3+/Te6+ partial ordering within the honeycomb-like two-dimensional [GaTeO6]3- anionic layer leads to the loss of the inversion center between Ga3+ and Te6+; however the inversion center on the 3̄-roto-inversion axis is preserved, thereby resulting in a 2-fold PbSb2O6-type superstructure by doubling the c-axis associated with a structural symmetry descending from the original P3̄1m to P3̄1c symmetry. In contrast, LaMnTeO6 (P21/c) adopts a monoclinically distorted 4-fold superstructure with lattice dimensions of a ≈ aH, b ≈ √3aH, c ≈ 2cH, where aH and cH represent the lattice parameters of trigonal PbSb2O6. The formation of this P21/c-superstructure is attributed to the combination of complete Mn3+/Te6+ ordering and the first-order Jahn-Teller distortion of Mn3+ with the electronic configuration of d4. Such a monoclinic distortion can effectively lift the Mn3+ spin moments arranged on the triangular sublattice, resulting in a sharp peak for antiferromagnetic transition, which is in stark contrast to subtle magnetic transitions for PbSb2O6-type tellurates AMn(VI)TeO6 (A = alkaline earth and Pb2+) and LnCrTeO6 (Ln = rare earth) with higher structural symmetry. Our findings highlight that the electronic configuration effects of M-cations play a critical role in controlling the structure symmetry of LaMTeO6, providing a strategy to fine-tune the crystal structures and physical properties.

Mechanistic explanation and influence of molecular structure on chemical degradation and toxicity reduction by hydroxyl radicals.

This study explored the influence of structural characteristics of organic contaminants on the degradation during an advanced oxidation process (AOP). The target contaminants were acetaminophen (ACT), bisphenol A (BPA), and tetracycline (TC). The Fenton process was selected as the model process in which major reactive species of hydroxyl radicals in most AOPs are generated for target compound degradation. The optimal reagent concentration ratio was [Fe2+]/[H2O2] = 0.5 mM/0.5 mM in an acidic condition, resulting in 83.49%, 79.01%, and 91.37% removals of ACT, BPA, and TC, respectively. Contrarily, the mineralization rates were apparently lower compared to their respective removal efficiencies. Experimental observation also suggested that the aromatic structure was rather difficult to degrade since their unsaturated electron clouds would hinder the attack of hydroxyl radicals due to electric repulsion. The preferred attacking sites of an aromatic ring differ due to the functional groups and structure symmetry. However, the electrophilic attack of the hydroxyl radical is the major reaction for decomposing aliphatic structures of cyclic or branched organics, resulting in the highest removal and mineralization of TC among these three tested chemicals. In addition, an apparent removal of a contaminant may not necessarily reduce its toxic impact on the environment.