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Conventional laser cavities require discontinuity of material property or disorder to localize a light field for feedback. Recently, an emerging class of materials, twisted van der Waals materials, have been explored for applications in electronics and photonics. Here we propose and develop magic-angle lasers, where the localization is realized in periodic twisted photonic graphene superlattices. We reveal that the confinement mechanism of magic-angle lasers does not rely on a full bandgap but on the mode coupling between two twisted layers of photonic graphene lattice. Without any fine-tuning in structure parameters, a simple twist can result in nanocavities with strong field confinement and a high quality factor. Furthermore, the emissions of magic-angle lasers allow direct imaging of the wavefunctions of magic-angle states. Our work provides a robust platform to construct high-quality nanocavities for nanolasers, nano light-emitting diodes, nonlinear optics and cavity quantum electrodynamics at the nanoscale. Twisted photonic graphene superlattices enable the realization of high-performance room-temperature magic-angle lasers.

Topological insulators are materials that behave as insulators in the bulk and as conductors at the edge or surface due to the particular configuration of their bulk band dispersion. However, up to date possible practical applications of this band topology on materials’ bulk properties have remained abstract. Here, we propose and experimentally demonstrate a topological bulk laser. We pattern semiconductor nanodisk arrays to form a photonic crystal cavity showing topological band inversion between its interior and cladding area. In-plane light waves are reflected at topological edges forming an effective cavity feedback for lasing. This band-inversion-induced reflection mechanism induces single-mode lasing with directional vertical emission. Our topological bulk laser works at room temperature and reaches the practical requirements in terms of cavity size, threshold, linewidth, side-mode suppression ratio and directionality for most practical applications according to Institute of Electrical and Electronics Engineers and other industry standards. We believe this bulk topological effect will have applications in near-field spectroscopy, solid-state lighting, free-space optical sensing and communication.The interface between photonic crystals with distinct in-band topologies confines electromagnetic modes and gives rise to lasing emission in the bulk.

Organic molecular crystals with controllable bending angles are crucial interconnectors in integrated optoelectronic chips, which can precisely guide optical signals along a predetermined path to achieve effective optical path steering. Nevertheless, current methods of tailoring molecular crystals with desired bent geometric features yet without fractured bending interface has not yet been fully realized. Here, we addresses this issue by proposing a universal “molecular cocrystal” strategy that introduces directional charge-transfer non-covalent interactions into molecular systems to weaken the original interactions, thereby triggering the spontaneous deformation transition from crystal slippage to bending. Significantly, a diverse range of self-assembled bent crystals with accurate angles ranging from 61.8° to 85.0° have been synthesized without destroying the structural integrity of the crystals. The proposed strategy is also applied to construct hierarchical bent microstructures with 2 to 6 bends. These as-prepared bent crystals exhibit excitation position-dependent anisotropic optical behaviors, which are applied into the photonics switch with adjustable on/off ratio. This methodology offers a versatile pathway to purposely design bent crystals with tailored angles, thereby laying a structural foundation for the on-chip organic optoelectronics. Organic molecular crystals with controllable bending angles are crucial interconnectors in integrated optoelectronic chips but current methods of tailoring bent geometric features in molecular crystals without fracturing remain limited. Here the authors proposing a molecular cocrystal strategy that introduces directional non-covalent interactions into molecular systems to weaken the original interactions triggering the spontaneous deformation.

Topological photonics offers the potential to develop quantum light sources with inherent robustness against structural disorders. To date, topologically protected edge or corner states have been investigated for this purpose. Here, for the first time, we exploit a topological bulk state with vertical directionality to enhance the light emission from a single semiconductor quantum dot (QD). An irregular ‘Q’-shaped cavity is applied for establishing topological robustness. We experimentally demonstrate a 1.6-fold Purcell enhancement of single-photon emission in the topological bulk cavity, with tolerance to the emission wavelength or the positioning of the coupled QD. Simulations indicate that such a QD-cavity coupling system can retain a Purcell factor exceeding 1.6 under a broad spectral detuning range of 8.6 nm or a coverage area of 2.5 μm 2 . Furthermore, the optimized cavity structure integrated with a reflector predicts a high single-photon extraction efficiency up to 92%. Our results offer a novel approach to develop topologically protected quantum light sources with high extraction efficiency and robust QD-cavity interaction against irregular cavity boundaries. We demonstrate a single-photon source based on topological bulk cavity, achieving high extraction efficiency and robust QD-cavity interaction against irregular cavity boundaries.

In our Letter (Phys. Rev. Lett. vol. 125, 013903 (2020)), we reported topological vortex lasers based on spin-momentum-locked edge modes. We observed that the near field spin and orbital angular momentum has a one-to-one far-field radiation correspondence of circular polarization and orbital angular momentum respectively. Sun et al. in their Comment (arXiv:2009.04700v1), however, argued that we did not perform numerical simulations on the near field information of our experimentally studied topological edge modes, and our mode assignment was mistaken and spoiled the one-to-one correspondence. However, we will show that their arguments are wrong. Furthermore, we will show that the Eqs. (1) and (2) and the phase windings in their Comment are wrong.

Ordered atomic-scale superlattices on surface hold great interest both for basic science and for potential applications in advanced technology. However, controlled fabrication of superlattices down to atomic scale has proven exceptionally challenging. Here we demonstrate the segregation-growth and self-organization of ordered S atomic superlattices confined at the interface between graphene and S-rich Cu substrates. Scanning tunneling microscope (STM) studies show that, by finely controlling the growth temperature, we obtain well-ordered S (sub)nanometer-cluster superlattice and monoatomic superlattices with various periods at the interface. These atomic superlattices are stable in atmospheric environment and robust even after high-temperature annealing (~ 350 oC). Our experiments demonstrate that the S monoatomic superlattice can drive graphene into the electronic Kekulé distortion phase when the period of the ordered S adatoms is commensurate with graphene lattice. Our results not only open a road to realize atomic-scale superlattices at interfaces, but also provide a new route to realize exotic electronic states in graphene.

It is of keen interest to researchers understanding different approaches to confine massless Dirac fermions in graphene, which is also a central problem in making electronic devices based on graphene. Here, we studied spatial confinement, magnetic localization and their interactions on massless Dirac fermions in an angled graphene wedge formed by two linear graphene p-n boundaries with an angle 34. Using scanning tunneling microscopy, we visualized quasibound states temporarily confined in the studied graphene wedge. Large perpendicular magnetic fields condensed the massless Dirac fermions in the graphene wedge into Landau levels (LLs). The spatial confinement of the wedge affects the Landau quantization, which enables us to experimentally measure the spatial extent of the wave functions of the LLs. The magnetic fields induce a sudden and large increase in energy of the quasibound states because of a pi Berry phase jump of the massless Dirac fermions in graphene. Such a behavior is the hallmark of the Klein tunneling in graphene. Our experiment demonstrated that the angled wedge is a unique system with the critical magnetic fields for the pi Berry phase jump depending on distance from summit of the wedge.

Water transport is vital for the durability of ultra-high performance concrete (UHPC) in engineering, but its absorption behavior requires further comprehension. This study investigates the impact of silica fume (SF) and metakaolin (MK) on water absorption in UHPC matrix with a high volume of limestone powder (LS) under two curing temperatures, and the variation in water transport with pore size obtained by low field nuclear magnetic resonance (LF-NMR). Relations between cumulative water absorption with other properties were discussed, and the pore size distribution (PSD) measured by Mercury intrusion porosimetry (MIP) was compared with that determined by LF-NMR. Results showed that MK outperformed SF in reducing water absorption in UHPC matrix, containing 30% LS under steam curing due to the synergistic effect between MK and LS. The incorporation of LS greatly affected the water absorption process of UHPC matrix. In samples without LS, capillary and gel pores absorbed water rapidly within the first 6 h and slowly from 6 h to 48 h simultaneously. However, in samples with 30% LS, gel pore water decreased during water absorption process due to the coarsening of gel pores. MK was able to suppress gel pore deterioration caused by the addition of a large amount of LS. Compared with PSD measured by MIP, NMR performed better in detecting micropores (<10 nm).

To examine the research trends and hotspots of the application of cognitive reserve in stroke cognitive impairment using CiteSpace and provide a reference for developing effective measures to reduce the incidence of cognitive impairment in these patients. Using CiteSpace software, a visual analysis of 860 included articles related to cognitive reserve in stroke cognitive impairment patients was performed. Relevant literature regarding the application of cognitive reserve in poststroke cognitive impairment was retrieved from the Web of Science core collection database from January 2010 through January 2024. Citespace 6.3.R1(64-bit) was employed to visualize and analyze literature data, including general literature analysis, national publication distribution, literature cocitation, journal co-citation, keyword co-citation, keyword clustering, literature co-citation, and literature co-citation clustering. A total of 860 articles were retrieved, indicating a rising trend in publications in this field, with the United States leading in publication count and FRONT NEUROL being the most frequently cited journal. The most frequently cited references usually focus on the prevention and influence factors of cognitive impairment and dementia. After eliminating keywords similar to the search terms, the top 3 keywords with the highest frequency and highest mediated centrality were dementia, cognitive influences, and risk factors, while education, influences, and cognitive assessment were emerging research focuses.

In-depth genome characterization is still lacking for most of biofuel crops, especially for centromeres, which play a fundamental role during nuclear division and in the maintenance of genome stability. This study applied long-read sequencing technologies to assemble a highly contiguous genome for yellowhorn ( Xanthoceras sorbifolium ), an oil-producing tree, and conducted extensive comparative analyses to understand centromere structure and evolution, and fatty acid biosynthesis. We produced a reference-level genome of yellowhorn, ∼470 Mb in length with ∼95% of contigs anchored onto 15 chromosomes. Genome annotation identified 22,049 protein-coding genes and 65.7% of the genome sequence as repetitive elements. Long terminal repeat retrotransposons (LTR-RTs) account for ∼30% of the yellowhorn genome, which is maintained by a moderate birth rate and a low removal rate. We identified the centromeric regions on each chromosome and found enrichment of centromere-specific retrotransposons of LINE1 and Gypsy in these regions, which have evolved recently (∼0.7 MYA). We compared the genomes of three cultivars and found frequent inversions. We analyzed the transcriptomes from different tissues and identified the candidate genes involved in very-long-chain fatty acid biosynthesis and their expression profiles. Collinear block analysis showed that yellowhorn shared the gamma (γ) hexaploidy event with Vitis vinifera but did not undergo any further whole-genome duplication. This study provides excellent genomic resources for understanding centromere structure and evolution and for functional studies in this important oil-producing plant.