The 2023 Nobel Prize in Physics recognized attosecond science and technology, which allows us to understand and control the properties of matter by accessing electron dy-namics at the Angstrom length scale. Attosecond science and technology are currently being applied to investigate all phases of matter and have garnered particular attention in the field of light-induced processes in molecules. After two decades of development, an attosecond perspective on molecular processes has become a tangible reality thanks to advanced experiments and theories. However, so far, this has only been applied to small model systems. This article discusses the current state of the field and explores how it could expand to include the study of complex structures, including large biomolecules.
The region of convergence of the spherical harmonic expansion is determined by the (generally complex) singularities of the gravitational potential. This complex analysis perspective is at the heart of recent rigorous results concerning the divergence properties of the spherical harmonic expansion. In this paper we build physical intuition for these general mathematical results using illustrative examples (some familiar and some new) of idealized planets for which the analysis is particularly explicit. This approach provides new methods to determine the region of convergence, without computing and analyzing expansion coefficients, and gives a novel geometric understanding of the divergence phenomenon. It also explains the fundamental origin of the numerical instabilities inherent to polyhedral models of planets. For the sake of clarity, we illustrate this new approach for the special case of axisymmetric planets of constant density, with explicit comparisons, but the key ideas do not rely on these restrictions.
Emission from quantum dots is inherently broadband, isotropic, and unpolarized, exhibiting poor spatial and temporal coherence that largely limits their applications in directional and polarization-controlled light sources. While resonant metasurfaces supporting symmetry-protected BICs can enhance emission through high-Q radiative resonances near the BIC in momentum space, their rigid symmetries confine emission to fixed directions and polarization states, preventing robust emission control. Here, we overcome the symmetry-imposed limitations by introducing a symmetry-free resonant metasurface that transforms incoherent quantum dot emission into multiple directional illuminations with designable polarizations and enhanced spatial and temporal coherence. Our recipe allows continuous and robust control of emission while preserving resonance quality. Our approach unifies coherence enhancement and emission shaping within a unified framework, establishing a scalable and versatile platform for active photonic chips and tunable quantum light sources.
For over thirty years, the definition of the diffusion coefficient in light transport has been the subject of persistent debate. Its canonical expression includes an explicit dependence on absorption, violating a fundamental scaling property of the radiative transfer equation (RTE). In the time domain (TD), evidence shows that the correct definition is independent of absorption, yet absorption-dependent formulations unfortunately remain common in practical data analysis. In the continuous-wave regime, the radial decay of the RTE can be reproduced by an absorption-dependent coefficient, but this does not imply that steady-state transport is genuinely diffusive. Here, this controversy is resolved through an exact consistency test based solely on the requirement that diffusion converges to the RTE in the limit of infinite propagation. In the TD, we prove that the absorption-independent coefficient is both necessary and sufficient for exact long-time convergence. In the continuous-wave regime, we prove analytically that no scalar diffusion coefficient can make diffusion asymptotically equivalent to the RTE when absorption is nonzero: matching the dominant attenuation length fixes one coefficient, whereas matching the residue requires a different one. We further show that this failure is not caused by any finite set of ballistic or few-scattering contributions, and quantify the intrinsic error introduced by incorrect parameterizations in idealized absorption-retrieval scenarios. These results establish the time-domain formulation as the only self-consistent reference and call for a re-examination of how diffusion is applied in optical transport studies.
Abstract Strain relaxation at lattice-mismatched interfaces is critical for epitaxial growth and high-quality single-crystal films. While van der Waals (vdW) epitaxy is considered as a promising platform due to its high tolerance to lattice mismatch, its actual response to lattice mismatch remains largely unexplored. Here, we investigate the effect of lattice mismatch on vdW interfaces by epitaxially growing MoS 2 on WS 2 or WSe 2 substrate. annular dark-field scanning transmission electron microscopy reveals that MoS 2 /WS 2 with a negligible lattice mismatch of ∼0.22% forms a fully commensurate structure, whereas MoS 2 /WSe 2 with a large lattice mismatch of ∼3.96% exhibits non-uniform moiré patterns, characteristic of an incommensurate interface. Detailed analysis shows that the MoS 2 /WS 2 hetero-bilayers exhibit perfectly aligned structure through compression of MoS 2 , whereas the MoS 2 /WSe 2 hetero-bilayers show elongation and rotation of moiré orientation driven by tensile strain. Notably, even small twist angles induce significant changes in moiré orientation, resulting in bent fringes that are indicative of local rotational distortions. Large lattice mismatch drives localized lattice distortion, where rotation of the MoS 2 lattice emerges as an energetically favorable mechanism for strain release, in contrast to commensurate alignment in small-mismatch systems. Our results establish moiré pattern analysis as a powerful framework for directly visualizing spatially varying strain and its relaxation pathways in vdW hetero-bilayers. Our work reveals previously inaccessible interfacial deformation modes in vdW hetero-bilayers and establishes moiré analysis as a powerful platform for strain engineering in 2D electronic and optoelectronic materials.
Abstract Actinide systems continue to raise many unanswered questions on topics involving the number of electrons in valence states, the degree of f-electron localization, and the character of their chemical bonding. Their partially filled 6d and 5f valence shells are responsible for most of their complex behaviour. Understanding the intricate electronic structure of actinides requires the use of advanced experimental and theoretical techniques. Among the experimental approaches, resonant inelastic x-ray scattering and x-ray absorption near edge structure in the high energy resolution fluorescence detection mode at the actinide M 4,5 edges have proven to be powerful techniques for investigating their electronic structure. Here, we review the fundamentals of these x-ray spectroscopies and the theoretical advances in electronic structure calculations using data recorded on 5f electron systems at the An M 4,5 edges (An = Th, U, Np, Pu).
This review explores different colloidal systems and their crystals as well as their special case namely-mesocrystals. First, we highlight recent advances in fabrication methods of colloidal crystals (mesocrystals) and then describe small-angle and ultra-small-angle x-ray scattering from colloidal assemblies organized from particles of different shape. Here, we already introduce different types of defects that are present in colloidal crystals. Next, we go to a modern description of angular x-ray cross-correlation analysis and its applications on colloidal and mesocrystalline materials. After that we discuss phase retrieval techniques, namely coherent x-ray diffraction imaging and ptychography, as emerging tools for structural characterization of colloidal crystals and mesocrystals. We conclude with perspectives on the opportunities that will be provided by the 4th generation synchrotron sources for studying colloidal crystals and mesocrystals.
Skyrmion family members, including skyrmions, merons, and skyrmioniums, have been observed in diverse physical systems, yet their coexistence and transformation within a single controllable platform remain challenging. Here, we propose and experimentally demonstrate a bilayer twisted moiré elastic system that enables the generation of multiple skyrmion family members with different topological charges. By constructing three-dimensional displacement vector fields, we establish a framework describing the evolution of topological invariants under twist-induced symmetry modulation, thereby governing controlled transitions and the stable coexistence of different skyrmion textures. In addition, manipulating the Lamb-wave phase introduces discontinuous transport of the topological textures, thereby revealing phason-like dynamics within the quasiperiodic structure. Together, these results provide a versatile route for controlling topological textures and open new possibilities for the design of integrated topological wave devices.
This review systematically summarizes the principles, technological advancements, and diverse applications of Stokes-vector and Mueller-matrix polarization imaging (PI). The polarization of light is a fundamental property that provides unique and valuable information about the interaction between light and matter. While traditional polarimetry is limited to point-by-point measurements, PI captures the polarization state in a two-dimensional scene, generating a spatial map of parameters for complex and heterogeneous systems. The Stokes-Mueller formalism is the only complete mathematical tool for polarization analysis, using the Stokes vector to describe the light's state and the Mueller matrix as the transfer function to fully characterize the polarization-altering properties of any medium, including complex depolarizing tissues. The evolution of PI from time-sequential to snapshot paradigms represents a pivotal shift, driven by the pressing need for real-time, motion-artifact-free characterization of dynamic systems. While time-sequential systems laid the foundational framework, their inherent trade-off between acquisition speed and polarization completeness has spurred intense innovation in snapshot methodologies. This transition is not merely a technical improvement but a fundamental enabler for applying polarization analysis toin vivobiological processes and real-time industrial inspection. Applications of PI are wide-ranging, including label-free diagnostics for cancer detection, non-destructive analysis of anisotropic materials, polarization-enhanced target detection, and so on. A future direction is the convergence of PI with hyperspectral detection to form 'hyper-Stokes/Mueller imaging,' which promises unprecedented specificity and real-time capability.
Power independence and system simplicity are paramount for robust droplet manipulation in decentralized applications, including point-of-care diagnostics and wearable biosensors. However, conventional active microfluidics for droplet manipulation are often bottlenecked by the requirement for high-voltage power supplies, intricate electrode networks, or magnetic additives that escalate system complexity and restrict portability. Here, we report a self-sustained electric-field-based electrophoretic platform (SELF-EP) that achieves autonomous droplet charging and sophisticated manipulation, entirely eliminating the need for external power sources. This is enabled by a specialized SELF emitter engineered to retain quasi-permanent surface charges, providing a continuous and stable SELF. Rather than direct charge injection, SELF drives electrostatic induction, drawing charges from ground to induce a net charge on droplets. Through integrated theoretical modeling and experimental validation, we demonstrate that the SELF-EP allows for deterministic control of droplet charge and supports on-demand droplet manipulation with various spatial configurations. Notably, we show parallelized control of multiple droplets and realize complex, programmable functions such as self-alignment and routing via precise spatial patterning of surface charges. Our SELF-EP paradigm bypasses the need for active electronics, offering a minimalist yet multifunctional strategy that significantly expands the boundaries of autonomous microfluidic and biomedical technologies.
Colloidal quantum dots (QDs) offer size-tunable optoelectronic properties and solution processability, yet achieving uniformly packed emissive layers remains a bottleneck for high-performance quantum-dot light-emitting diodes (QLEDs). Here, we report a machine learning -guided solvent optimization strategy to produce homogeneous QD films. Five representative solvent parameters are evaluated, and multiple regression models are trained against film uniformity derived from atomic force microscopy. Among them, support vector regression provides the highest predictive accuracy for film homogeneity. Guided by these predictions, we formulate a mixed solvent that closely matches the target profile, yielding superior packing homogeneity, which is confirmed by grazing-incidence small-angle x-ray scattering. QLEDs fabricated with this formulation exhibit an external quantum efficiency of 20.6% and an operational lifetime of 468.5 h at 20 000 cd m-2, surpassing all single-solvent controls. These findings establish packing homogeneity as a decisive factor for device performance and introduce a generalizable and scalable framework for data-driven design of solution-processed devices, holding strong potential for next-generation optoelectronic systems.
Quantum information theory, the formalism for representing information contained in quantum systems, is based on complex Hilbert spaces. It was recently shown that in quantum networks involving three parties with nontrivial locality constraints, this formalism predicts correlations that cannot be explained by real quantum theory, a variant of quantum mechanics based on real Hilbert spaces. In this work, we study a scenario withparties sharing quantum systems in a star network. We then construct a multipartite Bell inequality that exhibits a gap between quantum theory and its variant based on real numbers, which grows linearly with, and is thus arbitrarily large in the asymptotic limit. This implies, that, as the number of parties grows, Hilbert space formalism based on real numbers becomes exceedingly worse at describing complex networks of quantum systems. We also compute the tolerance of this gap to experimental errors.
The standard model of photography is that lenses form images and focal planes capture those images. Over the past two decades, however, cameras have been transformed from devices that record focal images into analog-to-digital converters that transform massively parallel optical signals into serial electronic data. Under this new model, one may choose to maximize the quality and quantity of captured information, rather than focal image quality. Here we review the nature of the optical data stream and consider lens and focal plane designs that improve information capture capacity. After maximizing information capacity, the challenge of converting this information to digital data requires novel read-out and compression. We review strategies for approaching physical information limits under realistic size, power, and bandwidth constraints. Multiscale monocentric (spherical primary optics combined with arrays of secondary micro-cameras, each imaging a narrow subfield) and array lens architectures relax unfavorable geometric scaling by trading monolithic optics for co-designed system-level integration (jointly optimized optics, focal-plane, and readout subsystems). Metaoptic and mode-sorting focal plane filters implement richer projection operators that sample spectral, polarimetric, and coherence features without requiring exhaustive scanning. Finally, because readout and computation dominate energy at high throughput, we highlight architectures that perform dimensionality reduction before (or during) digitization, including integrated photonic encoders and multilayer optical projections coupled to detection and learned decoding. Together, these developments motivate a shift from cameras optimized to produce 2D images toward cameras engineered as end-to-end information channels, co-designing optics, focal-plane, and readout to deliver more task-relevant measurements per photon and per joule.
Synchronization is a fundamental emergent phenomenon observed across a wide range of natural and engineered systems. Understanding the stability of a synchronization phenomenon is crucial for ensuring functionality in various complex systems. The master stability function (MSF) framework has emerged as a powerful and elegant tool for analyzing the stability of synchronization in coupled dynamical systems. By separating the effects of the node dynamics from the network structure, the MSF offers deep insights into synchronization behavior. However, a major challenge lies in determining the MSF for complex dynamical networks driven by nonlinear interaction mechanisms. These mechanisms introduce additional complexity due to the intricate connectivity of the interacting elements and the complex dynamics governed by nonlinear processes, diverse parameters, and the higher dimensionality of the system. Although MSF analysis has been widely used for more than past 25 years, a comprehensive and systematic investigation of MSF across various networked systems is still lacking. In this article, we present a simplified and unified analysis for the MSF in various undirected and directed networked systems. We begin by formulating the MSF framework in pairwise coupled identical systems and extend our analysis to directed networks and multilayer networks, considering both intralayer and interlayer interactions. Furthermore, we analyze the MSF formalism for higher-order networks. To facilitate understanding, we complement the theoretical developments with numerical analysis of synchronization stability in coupled systems. We also propose algorithms for computing the MSF, identifying stability regimes, and classifying the MSF behaviors. Overall, the primary goal of this review is to present a systematic study of the MSF in various coupled dynamical networks in a clear and structured manner, making this powerful tool more accessible. Furthermore, we highlight underexplored areas in the application of the MSF and discuss emerging directions, such as estimating the MSF using machine learning approaches.
Van der Waals heterostructures integrated by two-dimensional (2D) transition metal dichalcogenides (TMDs) hold great potential for engineering promising exciton phenomena, particularly interlayer excitons (IXs) featuring extended lifetimes and permanent out-of-plane electric dipole moments. While electrically controllable IX emission has been extensively explored in TMD heterobilayers, reconfiguring their band alignment to achieve selected exciton states and exploit these states for novel excitonic functionalities remains an urgent challenge. Here, we demonstrate dynamic exciton control by electrically tunable band alignment transitions between type-II and type-I configurations in WS2/(iso-BA)2PbI4heterostructures, enabling reversible conversion between charged interlayer (IX±) and charged intralayer (X-) excitons. By tailoring these exciton states, we achieve two critical functionalities: (i)7μm ON/OFF control of exciton transportvia transition between delocalized IX±(ON) and confined X-(OFF) states; (ii)valley polarization switchingwith a 16.3 ON/OFF ratio, leveraging distinct spin-valley configurations of IX±(unpolarized) and X-(polarized). Unlike twist-angle-dependent TMD heterobilayers, this platform operates independently of stacking alignment, establishing a broadly hybrid 2D system as a practical paradigm towards programmable nanophotonic circuits.
Negative thermal expansion (NTE) refers to volume contraction upon heating, but the intrinsic complexity of its physical mechanisms presents a fundamental challenge. α -Cu 2 V 2 O 7 exhibits significant anisotropic NTE over a wider temperature range; however, its NTE mechanism has not been clearly elucidated. Herein, we systematically investigate the NTE mechanism of α -Cu 2 V 2 O 7 using neutron powder diffraction, synchrotron radiation x-ray diffraction, and temperature- and pressure-dependent Raman spectra, and density functional theory calculations across 5–800 K. The structure exhibits a second-order Jahn–Teller (SOJT) effect, which is the primary cause of off-centering within the quasi-CuO 6 octahedra. As temperature increases, the SOJT effect weakens, reducing the distortion of the driving force for off-centering; this causes the Cu atoms to shift in opposite directions, increasing symmetry. The anti-off-centering displacement of the Cu atoms toward the O 4(long) atoms in the quasi-CuO 6 octahedra compresses the Cu···Cu zigzag chains and reduces the spacing between orthogonal chains, resulting in the NTE behavior of α -Cu 2 V 2 O 7 . This study reveals a novel mechanism whereby the SOJT effect governs the displacement and symmetry of Cu atoms, providing crucial insight into the origin of NTE behavior in α -Cu 2 V 2 O 7 . These findings could help the community advance the understanding of NTE in anisotropic materials.
In this work, we present an algorithmic treatment of the representation theory of the algebra of partially transposed permutation operators, denoted by A p , p d , which is a matrix representation of the abstract walled Brauer algebra. We provide an explicit and fully developed framework for constructing irreducible matrix units within the algebra. In contrast to the established earlier Gelfand–Tsetlin type constructions, the presented matrix units are adapted to the action of the subalgebra C [ S p ] × C [ S p ] , where S p is the symmetric group. What is more, the basis is constructed in such a way that it produces the decomposition of the algebra into a direct sum of ideals, in contrast to its nested structure considered before. The decomposition of this kind has not been considered before in full generality. Our method reveals a recursive scheme for generating irreducible matrix units in all ideals of A p , p d , offering a systematic approach that applies to small system sizes and arbitrary local dimensions. We apply the developed formalism to the algebra A 2 , 2 d and illustrate the algorithm in practice. In addition, using the constructed basis, we proved a novel contraction theorem for the elements from A 3 , 3 d , which is the starting point for further investigations.
Fermi arcs (FAs) in Weyl semimetals provide a unique platform for surface-state engineering, yet directly tracking of their evolution under surface tuning remains experimentally challenging. Here we theoretically propose that nonreciprocal charge transport can serve as a direct probe of Fermi arc Lifshitz transitions (FALT). We show that different surface terminations in Co 3 Sn 2 S 2 can produce finite and highly tunable second-order nonreciprocal signals, which can be further modulated by adjusting the surface potential. Strikingly, we show that the second-order conductivity exhibits sign changes as the Fermi arc connectivity is tuned across FALT driven by gating or chemical potential variation. This behavior arises from the chiral nature of electron velocities on the FAs, and is highly sensitive to surface termination and symmetry breaking. Our findings establish nonreciprocal transport as an electrically measurable fingerprint of FALT and propose new strategies that could be directly applied in devices for in situ engineering and detecting transport properties in topological materials.
