Browse Articles

Second-order topological insulators in Kekulé-patterned hexagonal biphenylene networks

Biphenylene network, a two-dimensional material, has recently been extensively studied, owing to its potential applications. Here, we introduce an experimentally synthesized configuration of hexagonal biphenylene network (h-BPN) as a second-order topological insulator (SOTI). We begin by discussing the higher-order topological origin of h-BPN, which is an extended model of the Kekulé lattice characterized by a multi-node π-conjugation. Through first-principles calculations and tight-binding model, we reveal SOTI in h-BPN, characterized by non-zero fractional corner charges. Furthermore, we show that by varying the number of biphenylene units, h-BPN exhibits adjustable second-order topological phases with alternating parity. Specifically, odd biphenylene indices in the h-BPN system correspond to a SOTI, while even indices result in a trivial insulator. We propose that the h-BPN evolves from the Kekulé lattice. These materials will have important applications in two-dimension devices as higher-order topological materials.

Spatiotemporal transcriptome and metabolome landscapes of cotton somatic embryos

Near-infrared photoluminescence from bismuth, a deep defect in cesium lead bromide perovskite

Bismuth has been investigated as a potential n-type dopant in hybrid lead halide perovskites, but its behavior in all-inorganic perovskites such as CsPbBr3 has not been thoroughly characterized. We show that Bi behaves as a deep defect in CsPbBr3 and gives rise to broad near-infrared emission, similar to its behavior in hybrid perovskites, but a phenomenon not previously reported in CsPbBr3. Using inverse temperature crystallization, we synthesized a series of Bi-doped CsPbBr3 crystals and quantified their Bi concentrations by inductively coupled plasma optical emission spectroscopy. Bi incorporation redshifted the absorption edge, and hybrid density functional theory calculations show that this increased absorption comes from excitation into the deep donor level of Bi, not from narrowing of the bandgap of CsPbBr3. All Bi-doped crystals emitted both narrow band-edge (2.37 eV) and broad defect-level (1.16 eV) photoluminescence, consistent with our theoretical prediction. Time-resolved photoluminescence measurements indicate that Bi incorporation decreases the lifetime of the band-edge emission and gives rise to long-lived defect emission. Power-dependent photoluminescence measurements conducted at 14 K show that the band-edge peak intensity scales as expected for a free or bound exciton, while the sublinear scaling of the infrared defect peak is consistent with recombination between a free hole and a trapped electron, as proposed by theory. These results demonstrate the quantitative accuracy with which current theoretical approaches predict defect behavior in halide perovskites; such theory is key to guiding the experimental development of doping in these materials.

Accelerated enzyme engineering by machine-learning guided cell-free expression

Compact 852 nm Faraday optical frequency standard

Optical clocks with high precision are practical and necessary in atomic physics, geodesy, gravitational wave measurement, etc. Transportability and environmental adaptability are two key indicators to measure the performance of frequency standards. Here, we utilized a highly robust atomic-filter-based Faraday laser as the local oscillator, and achieved two compact Faraday optical frequency standards based on 133Cs6S1/2|F=3⟩→6P3/2|F′=2⟩ and 6S1/2|F=4⟩→6P3/2|F′=5⟩ transitions at 852 nm, leveraging modulation transfer spectroscopy for laser frequency stabilization. The Faraday laser automatically aligns atomic transition spectral lines, due to the use of atomic filters as frequency selective elements. Therefore, the laser wavelength has strong robustness against environmental changes. This setup not only simplifies the operational complexity but also ensures frequency stability. By heterodyne beating between two such compact optical frequency standards, the beatnote achieved a short-term frequency stability of 1.68 × 10−13 at 3 s, remained at the 10−13 level for up to 400 s, and stayed below 2.7 × 10−12 for up to 1600 s, predominantly exhibiting white frequency noise. This underscores the potential of atomic-filter-based Faraday laser in realizing compact and stable frequency standards, mitigating coherent communication error rates, and enhancing the precision of quantum interferometric measurements. Moreover, this approach eliminates the continuous need for external monitoring and adjustments, thereby, offering a practical and robust solution for out of laboratory applications demanding high frequency stability.

Author Correction: The role of manganese in CoMnOx catalysts for selective long-chain hydrocarbon production via Fischer-Tropsch synthesis

Effect of Cr/Al ratio on the microstructure and mechanical properties of CoFeNiCrxAl1−x high-entropy alloys

Achieving strength-ductility and functional integration is a key issue to promote the application of alloys in the field of functional materials. CoFeNiCrxAl1−x alloys exhibit excellent magnetic and corrosion resistance properties; however, their mechanical properties remain underexplored and insufficiently understood. In this work, the microstructure and mechanical properties of CoFeNiCrxAl1−x alloys were investigated, and their intrinsic deformation mechanisms were elucidated. The results indicate that as Cr is gradually replaced by Al, the phase structure transforms from a single-phase face-centered cubic (FCC) structure to a dual-phase FCC and body-centered cubic (BCC), and finally to a BCC/B2 structure. Mechanical tests demonstrated that alloy hardness rises with higher Al content, with the Cr0Al1 alloy exhibiting a hardness approximately 3.3 times greater than that of the Cr1Al0 alloy. Notably, the Cr0.5Al0.5 alloy exhibits an optimal strength-ductility balance, with a yield strength increase in about 60% to 248 MPa and tensile strength increase in about 36% to 610 MPa, while maintaining nearly the same ductility as the Cr1Al0 alloy. The deformation mechanisms were found to be driven by solid solution strengthening due to severe lattice distortion, a high dislocation density resulting from reduced dislocation formation energy, the second-phase strengthening and interface strengthening via the micrometer-scale BCC phase, and twin-induced plasticity induced by the reduced stack fault energy. This work broadens the potential applications of CoFeNiCrxAl1-x alloys as versatile engineering and magnetic functional materials.

Construction and iterative redesign of synXVI a 903 kb synthetic Saccharomyces cerevisiae chromosome

Abstract The Sc2.0 global consortium to design and construct a synthetic genome based on the Saccharomyces cerevisiae genome commenced in 2006, comprising 16 synthetic chromosomes and a new-to-nature tRNA neochromosome. In this paper we describe assembly and debugging of the 902,994-bp synthetic Saccharomyces cerevisiae chromosome synXVI of the Sc2.0 project. Application of the CRISPR D-BUGS protocol identified defective loci, which were modified to improve sporulation and recover wild-type like growth when grown on glycerol as a sole carbon source when grown at 37˚C. LoxPsym sites inserted downstream of dubious open reading frames impacted the 5’ UTR of genes required for optimal growth and were identified as a systematic cause of defective growth. Based on lessons learned from analysis of Sc2.0 defects and synXVI, an in-silico redesign of the synXVI chromosome was performed, which can be used as a blueprint for future synthetic yeast genome designs. The in-silico redesign of synXVI includes reduced PCR tag frequency, modified chunk and megachunk termini, and adjustments to allocation of loxPsym sites and TAA stop codons to dubious ORFs. This redesign provides a roadmap into applications of Sc2.0 strategies in non-yeast organisms.

Realizing p-type InSb with enhanced thermoelectric performance via Cd doping

InSb is a promising mid-temperature thermoelectric material, and its n-type thermoelectric properties have been widely studied. For thermoelectric device applications, it is necessary to have p-type counterparts. Here, we report the realization of p-type InSb with enhanced thermoelectric performance via Cd doping. A high-power factor of 1.91 × 10−3 W m−1 K−2 is obtained in p-type In0.93Cd0.07Sb at 723 K due to the increased carrier concentration. Moreover, the lattice thermal conductivity is decreased to 2.0 W m−1 K−1 owing to the significant multiscale phonon scattering and the suppressed bipolar diffusion effect. Ultimately, the peak zT value of 0.40 is achieved at 723 K in p-type In0.93Cd0.07Sb, which surpasses most contemporary p-type InSb materials. This study demonstrates a simple strategy for fabricating p-type InSb with high performance and holds promise in advancing the development of InSb-based TE devices.

Photocatalytic upcycling of polylactic acid to alanine by sulfur vacancy-rich cadmium sulfide

Temperature stability of multilayer symmetric KNN-based ceramics with continuous phase transitions

Temperature sensitivity of the lead-free piezoelectric ceramics based on potassium sodium niobate (KNN) has posed a significant challenge for practical applications. In this study, we developed a multi-layer symmetric KNN matrix composite ceramic in a strategy of compositional symmetry to enhance the thermal stability of its piezoelectric properties. The optimized piezoelectric properties of d33 and kp can last up to 121 and 105 °C (setting 10% performance reduction as standard), superior to its single composition sample. Importantly, the compositional symmetry effectively addresses the deformation issue during ceramic sintering. This finding of stability in KNN matrix ceramics will facilitate its industrial-scale production processes.

Cryo-electron tomography pipeline for plasma membranes

Abstract Cryo-electron tomography (cryoET) provides sub-nanometer protein structure within the dense cellular environment. Existing sample preparation methods are insufficient at accessing the plasma membrane and its associated proteins. Here, we present a correlative cryo-electron tomography pipeline optimally suited to image large ultra-thin areas of isolated basal and apical plasma membranes. The pipeline allows for angstrom-scale structure determination with subtomogram averaging and employs a genetically encodable rapid chemically-induced electron microscopy visible tag for marking specific proteins within the complex cellular environment. The pipeline provides efficient, distributable, low-cost sample preparation and enables targeted structural studies of identified proteins at the plasma membrane of mammalian cells.

From localization to quantum-dot chains in self-formed core–shell InGaN nanowires emitting in the red

Self-formed core–shell InGaN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy on p-Si (111) are studied by temperature-dependent and time-resolved photoluminescence (PL) spectroscopy. Clear localization and associated photocarrier redistribution can be evidenced by the S-shape temperature dependence of the PL peak energy and inflection of the PL linewidth. An unexpected maximum of the integrated PL intensity as a function of temperature is observed. This maximum is identified as proof that the localized states behave as chains of quantum dots with reduced radiative lifetime due to the combination of strong two-dimensional lateral quantum confinement in the NW core with localization. This is underlined by the time-resolved PL measurements exhibiting a fast, sub-ns, single-exponential decay, in addition evidencing negligible quantum-confined Stark effect for efficient light sources emitting in the red.

Pupylation-based proximity labeling reveals regulatory factors in cellulose biosynthesis in Arabidopsis

Higher-order topological fermion phase and Weyl phonon phase in Li-intercalated graphene layers

Two-dimensional (2D) higher-order topological fermionic phases coexisting with intriguing topological phonon states have recently become a focal point of condensed matter research. However, the coexistence of the second-order topological phase and valley Weyl phonon features in 2D materials remains unexplored. In this Letter, we present a two-dimensional Li-intercalated graphene material family that serves as an ideal platform for demonstrating the coexistence of topological electron and phonon features. Our study, which utilizes first-principles calculations, investigates the structural, electronic, and topological properties of several Li-intercalated graphene materials. The higher-order topological phases are protected by C6 rotation and inversion symmetries in Li-C6 and Li-C6-Li layers, respectively, as confirmed by their calculated topological invariants (χ6, Z4). Topologically protected corner modes are noticed within the gapped bulk and edge states (in the armchair edge) in the nanoflake geometry of the Li-C6 compound. Notably, the phonon spectra of the Li-C6 and Li-C6-Li materials exhibit Weyl phonon nodes in the Brillouin zone where the phonon bands touch at the valley-high symmetry point. The presence of localized Berry curvature and robust topological phonon edge states further confirms the existence of Weyl phonon nodes in these materials. Our first-principles study predicts potential candidates for hosting the coexisting electronic and phononic features and highlights the technological aspects of Li-intercalated graphene materials.

A dual role of Cohesin in DNA DSB repair

Abstract Cells undergo tens of thousands of DNA-damaging events each day. Defects in repairing double-stranded breaks (DSBs) can lead to genomic instability, contributing to cancer, genetic disorders, immunological diseases, and developmental defects. Cohesin, a multi-subunit protein complex, plays a crucial role in both chromosome organization and DNA repair by creating architectural loops through chromatin extrusion. However, the mechanisms by which cohesin regulates these distinct processes are not fully understood. In this study, we identify two separate roles for cohesin in DNA repair within mammalian cells. First, cohesin serves as an intrinsic architectural factor that normally prevents interactions between damaged chromatin. Second, cohesin has an architecture-independent role triggered by ATM phosphorylation of SMC1, which enhances the efficiency of repair. Our findings suggest that these two functions work together to reduce the occurrence of translocations and deletions associated with non-homologous end joining, thereby maintaining genomic stability.

Theoretical studies of transient hydrodynamic phonon transport in two-dimensional disk geometry

Many phonon hydrodynamics phenomena, including heat vortices, wave and parabolic distributions of heat flux, which appear due to sufficient normal process, can also appear when there is insufficient normal process. In other words, a smoking gun of phonon hydrodynamics phenomena at the macroscopic level is still lacking. To find it, transient cooling phenomenon in two-dimensional materials is studied based on the phonon Boltzmann transport equation. A heating pulsed Gaussian laser beam is added at the center of two-dimensional disk and it continues to heat the system for a while under the environment temperature. After the heating laser is removed, results show that the transient temperature could be lower than the environment temperature and this phenomenon could only appear with sufficient normal process and insufficient resistive process, which is exactly a smoking gun of phonon hydrodynamics. In addition, the possibility of this phenomenon measured by transient Raman experiments is theoretically discussed. Numerical results show that given a single-layer suspended graphene disk sample with diameter 7 μm, this transient cooling phenomenon can appear in the temperature range of 50–150 K.

Hominin presence in Eurasia by at least 1.95 million years ago

Alkylamine-tuned MoOx with synergistic manipulation of interlayer spacing and oxygen vacancies toward advanced Li–S batteries

Lithium–sulfur (Li–S) batteries have been considered a promising next-generation energy storage device. However, the serious polysulfide shuttle effect and slow reaction kinetics hampered their development. Herein, alkylamine-tuned MoOx with synergistic manipulation of interlayer spacing and oxygen vacancies as a bifunctional mediator for separator modification (refer to as MOC/PP) in Li–S batteries is proposed. The increased interlayer spacing provides a rapid and stable pathway for Li+ diffusion, facilitating uniform Li+ deposition on lithium anode. Rich oxygen vacancies serve as active sites for efficient chemisorption and catalysis with polysulfide. As demonstrated by theoretical calculations and experimental results successively, MOC/PP efficiently captures and accelerates the redox reaction of polysulfide. Therefore, LiǁLi symmetric cells with MOC/PP exhibit stable cycling over 1000 h at a current density of 1 mA cm−2. The full cells deliver a notable discharge-specific capacity of 602 mAh g−1 at 5 C (1 C = 1675 mA g−1) and maintain stable cycling for 800 cycles at 1 C, with 0.07% capacity decay per cycle. Even under conditions of lean electrolyte (E/S = 7 μL mgs−1) and high sulfur mass loading (4.3 mg cm−2), the initial capacity exceeds 1200 mAh g−1.

A single residue switch mediates the broad neutralization of Rotaviruses