Physics

Abstract Slippery, mucus-coated body surfaces are widespread in aquatic vertebrates, but their contribution to locomotion is unclear. Fish mucus has long been proposed to reduce drag, yet direct experimental evidence of a swimming benefit is limited. A series of four mucus-inspired, lubricant-infused aluminum substrates incorporating SLIPS (slippery liquid-infused porous surfaces) were fabricated to assess the effects of a slippery coating on motion under both static (drag-based) and dynamic (propulsive) conditions. The aluminum substrates were textured by conversion of the surface to nanostructured aluminum oxyhydroxide (boehmite), chemically functionalized, and infused with synthetic Newtonian liquids spanning the viscosity range of measured trout mucus and compared to that of unstructured and lubricant-free controls. Viscosity measurements were also performed on skin mucus collected from brook trout (S. fontinalis). SLIPS-coated surfaces were found to reduce the static drag by up to 9.1% and enhance the lift-to-drag ratio by up to 8.7%. Furthermore, SLIPS coatings improved both the thrust and efficiency of flapping plates actuated in heave and pitch by up to 3.6% and 4.1%, respectively, with performance improvements observed over a broad range of motion parameters, lubricant chemistries, and viscosities. Boundary layer flow measurements over a flat plate revealed that SLIPS experienced a reduced skin friction drag of up to 5.2% under laminar flow conditions. Nanostructured, functionalized, lubricated coatings thus act both to reduce drag and to enhance the propulsive thrust and efficiency of fishlike propulsion, providing one explanation for the presence of such structures on a diversity of animal surfaces.

The creation of phototransistors based on perovskite field‐effect transistors (PFETs) represents an attractive option for the development of better optoelectronic devices due to the capability for solution processing, an adjustable bandgap, and excellent charge transport properties. The incorporation of organic/inorganic perovskite semiconductors into a field‐effect transistor architecture yields highly responsive, low‐noise, and gate‐controllable photodetectors. This review summarizes key areas of development for PFETs, including perovskite material systems, device structures, interface engineering strategies, and performance metrics. A detailed discussion of the mechanisms of carrier photogeneration, transport, trapping, and recombination is also provided, along with a summary of engineering strategies to broaden the spectral response through bandgap tuning and heterostructures. Although significant progress has been made in the development of PFETs, major technical issues associated with the long‐term stability of PFETs, hysteresis, and the scalability of PFETs over large areas continue to pose significant challenges for their practical use. Potential applications for PFETs in photodetection, imaging, sensing, and fully integrated optoelectronic circuit designs are discussed along with general thoughts on the research direction in this area.

We explore the intriguing topological itinerant magnet ${\mathrm{MgMn}}_{6}{\mathrm{Sn}}_{6}$, characterized by bilayer kagome Mn layers encasing a hexagonal Sn layer. Using ab initio density functional theory and dynamical mean-field theory calculations, we uncover the complex electronic properties and many-body configuration of its magnetic ground state. This frustrated many-body state stabilizes the ferromagnetic ground-state sector, providing the time-reversal--symmetry-broken background required for the nontrivial electronic structure. Consequently, the exchange-split topological bands and associated Berry-curvature response are intrinsically linked to the magnetic ground state. Our band dispersion calculations reveal a mirror symmetry-protected nodal line in the ${k}_{z}$ = 0 plane. When spin-orbit coupling is introduced, a gap is formed along the nodal line due to broken time-reversal symmetry with magnetic ordering, leading to substantial intrinsic Berry curvature. We identify Dirac fermions, van Hove singularities, and a flat band near the Fermi energy $({E}_{F})$, with spin-orbit coupling introducing a finite gap at key points. The unique proximity of the flat band to ${E}_{F}$ suggests potential instabilities. Spin-orbit coupling opens a 10 meV gap at the point of contact between the quadratic and flat bands, bestowing a nonzero ${\mathbb{Z}}_{2}$ invariant. This leads to a significant spin Hall conductivity. Despite the presence of large incoherent scattering due to electronic interactions, band crossings and flat band features persist at finite temperatures since the scattering does not impact these features near ${E}_{F}$. ${\mathrm{MgMn}}_{6}{\mathrm{Sn}}_{6}$ exhibits intriguing topological and magnetic properties, with promising applications in spintronics.

${\mathrm{Th}}_{2}{\mathrm{Zn}}_{17}\text{\ensuremath{-}}\mathrm{type}$ structure-based permanent magnets, such as ${\mathrm{Sm}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$, offer strong potential as alternatives to neodymium magnets (NdFeB), but their practical use is limited by phase stability and the scarcity of Sm. Ce-based counterparts, particularly ${\mathrm{Ce}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$, are attractive low-cost candidates, yet their intrinsic planar magnetic anisotropy restricts permanent-magnet performance. Here, we induce uniaxial magnetic anisotropy in ${\mathrm{Ce}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$ through two approaches: (i) Co substitution on the Fe sublattice and (ii) partial substitution of Ce with Sm. Combined density functional theory and experimental results show that both strategies modify the $3d\text{--}4f$ interactions and band filling, yielding magnetization values up to $\ensuremath{\sim}1.2\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ and magnetocrystalline anisotropy energies exceeding $1\phantom{\rule{0.28em}{0ex}}\mathrm{MJ}/{\mathrm{m}}^{3}$ for Co-alloyed compositions, with significantly larger anisotropy achieved upon Sm substitution. In addition, the Sm-substituted ${\mathrm{Ce}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$ samples exhibit enhanced high-temperature stability compared to ${\mathrm{Sm}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$. These findings demonstrate that ${\mathrm{Ce}}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{3}$-based alloys can deliver magnetic performance suitable for permanent-magnet applications while reducing cost and reliance on critical rare-earth elements, and they provide practical design guidelines for rare-earth-lean magnets for energy and industrial applications.

A rod with rounded ends is a noteworthy morphology, naturally encountered from large-scale roots to cells, and synthetically conceived down to nanomaterials. Rod-shaped anisotropic nanocrystals---especially those grown on pre-synthesized spherical seeds---play a major role in areas as different as photonics, cancer therapy, and photocatalysis. Nonetheless, despite decades of intense research, the anisotropic growth laws of nanorods (NRs) remain elusive. Here, we propose a general two-surface tension thermodynamic model that allows determining these axial and radial NR growth rates by reaction and diffusion. Depending on the initial seed size, three growth modes are predicted: either 3d, where both length and diameter grow simultaneously, 1d, where NRs just grow in one direction, and 1d-3d, showing the two growth modes sequentially. Modeling also shows that NRs lengthening and widening are driven by the surface tension ratio between the cylindrical core and the hemispherical tips. The confrontation of this model with kinetics data published on both high-symmetry face-centered-cubic (FCC) and lower-symmetry hexagonal close-packed (HCP) Wurtzite nanocrystals, as well as new experiments on Wurtzite CdSe-CdS NRs, confirms the existence of these three growth modes under reaction-limited conditions. From a practical point of view, they enable the determination of the axial/radial kinetic reaction rates along with surface tensions, and experimentally predict the seed-dependent growth and morphology of the NRs beyond the already well-established synthetic strategies for targeted applications. Finally, the few data published on the growth of Smectic A ligaments in the isotropic phase after a quench in temperature show a qualitative agreement with behaviors expected from a two-surface tension diffusion-limited mechanism.

Interfaces have always been a key for functional devices in condensed-matter physic. However, dynamic regulation of interfacial symmetry and the subsequent effects have still been underestimated, especially in bulk materials. Here, we show that the interfacial crystallographic symmetry can be precisely modulated by electric field induced oxygen vacancy rearrangement in bulk centrosymmetric semiconductors (TiO 2 , SrTiO 3 , etc.), resulting in tunable interface polarization. Our results show that the interface polarization of metal-semiconductor heterostructure can be reversibly modified in a nonvolatile manner, with a tunable electromechanical response varying from 6.79 to 9.07 p.m./V, which is comparable to common piezoelectric semiconductors (ZnO, GaN, MoS 2 , etc.). Substantial self-gated carrier transport in metal-semiconductor heterostructure is achieved, with a Schottky barrier tuned by 30.8 meV. Furthermore, the self-gated electronics effectively simplifies the complicated structures of logic devices, integrating logic and storage operations through programmable interface polarization. These findings offer a distinctive approach to design the interface symmetry and functionalities beyond the intrinsic limitation of bulk centrosymmetric materials.

Thermal transport in crystalline solids generally occurs via particle-like phonon propagation. Here, we demonstrate the dominant unusual wave-like phonon transport and high thermoelectric figure-of-merit (zT) of ∼1.42 at 673 K in crystalline TlCu 5 Se 3 due to the strong anharmonicity exerted by confined Cu dynamic disorder and Tl rattling. TlCu 5 Se 3 shows an intrinsic ultralow lattice thermal conductivity of (κ L ) 0.3–0.2 W m −1 K −1 across the temperature range of 294–673 K. Density functional theory calculations and ab-initio molecular dynamics simulations reveal that strong lattice anharmonicity arises due to confined dynamic disorder of the Cu sublattice. The complex knot-like structure with strong anharmonicity reduces phonon lifetime below the Wigner limit, leading to substantial inter-band phonon coupling and a dominant wave-like coherence. By further tuning cationic vacancies to optimize electrical transport, we achieve an enhanced zT of ∼1.7 at 673 K in TlCu 5-x Se 3 (x = 0.03–0.07), demonstrating that confined ion dynamics not only maintains ultralow κ L but also enhances thermoelectric performance without compromising the stability.

More than half of global primary energy is dissipated as low-grade waste heat, yet thermoelectric conversion remains constrained by the intrinsic coupling between phonon and charge transport. Here, we introduce graded interfacial size distribution as a thermodynamic design variable that breaks translational symmetry in multilayers, enabling anisotropic regulation of phonon-carrier transport. Using bismuth telluride (Bi 2 Te 3 )/metal [gold, silver, and platinum (Pt)] multilayers as a model system, we demonstrate that multiscale interface distributions induce broadband phonon suppression through the coexistence of interfacial scattering, coherent interference, and localization. This yields an ultralow cross-plane thermal conductivity of 0.22 watts per meter per kelvin and a high room-temperature ZT of 1.51 in Bi 2 Te 3 /Pt films. Concurrently, asymmetric metal-semiconductor interfaces create quasi–two-dimensional accumulation channels that enhance in-plane carrier mobility while preserving energy filtering, delivering a power factor of 176.2 microwatts per centimeter per square kelvin at 300 kelvin. The graded architecture enables high performance in both vertical and flexible planar devices, illustrating a general strategy in which interface distribution, not merely composition, governs anisotropic heat-charge transport. Our findings establish statistical interface engineering as a platform for thermoelectric energy harvesting and solid-state cooling.

Dynamic strain offers a promising route to manipulate tightly bound excitons in two-dimensional semiconductors. Its impact, however, has so far been inferred primarily from time-averaged or spatially integrated measurements. In particular, for dynamic strain driven by surface acoustic waves (SAWs), the relatively small strain amplitude and competing piezoelectric effects have hindered direct access to the real-time evolution of exciton emission energy and recombination dynamics within a single acoustic cycle. Here we report a fully phase-synchronized, multidimensional spectro-temporal-spatial visualization of exciton emission in monolayer tungsten diselenide driven by propagating SAWs. By integrating phase-resolved microscopy and interferometric surface displacement measurements, we achieve simultaneous mapping of exciton emission energy, photoluminescence intensity, linewidth, and decay dynamics and directly correlate them with the dynamic strain field. Our work establishes propagating acoustic strain as a powerful platform for deterministic exciton control and provides a comprehensive framework for exploring nonequilibrium exciton dynamics in low-dimensional materials.

The laminar nature of blood flow and the resulting boundary layer pose substantial challenges for transverse mass transport in blood vessels, limiting intravascular biomedical applications such as targeted delivery, thrombolysis and biomarker enrichment. Herein, we develop a ciliated intravascular millirobot, CiliaVine, for active manipulation of particle and cell collectives through flow regulation. Actuated by tailored magnetic fields, soft cilia on the robot oscillate in different modes, generating desired flow patterns for flow regulation. CiliaVine enhances the transverse transport that is otherwise suppressed under laminar flow, driving circulating collectives from the vessel center toward the vessel wall for drug penetration, or reversing transport for thrombus residue clearance. Flow regulation is investigated in a vascular model using fluorescent tracer particles. Enhanced targeted drug delivery and accelerated thrombolysis enabled by the robot are validated. Circulating tumor cell (CTC) enrichment is evaluated using cancer patient blood and in tumor-bearing rabbits, revealing its effectiveness in physiological environments and its potential for intravascular rare-cell enrichment.

Nonlocal metamaterials have recently attracted considerable attention across different areas of wave physics, owing to their ability to translate long-range interactions among meta-atoms into a wide array of wave vector-dependent responses and functionalities. Here, we introduce nonlocal transmission-line metamaterials (TL MTMs) as a versatile platform to investigate and engineer nonlocality in the microwave frequency regime. We first establish a concise theoretical framework for nonlocal TL MTMs based on circuit and network theory, from which we derive the general dispersion relation for TL MTMs with arbitrarily complex nonlocal coupling configurations. Building on this foundation, we demonstrate how such structures can be used to synthesize nearly arbitrary even-symmetric dispersion relations, effectively linking nonlocal circuit parameters to prescribed dispersion profiles. We then introduce time-switched nonlocal TL MTMs, a class of metamaterials with time-varying nonlocality in which the nonlocal branches are dynamically activated as an electromagnetic pulse propagates through the structure. This platform enables complex transformations on a propagating pulse, as well as the excitation of modes with positive, negative, and zero group velocity. Last, we experimentally validate our theoretical and numerical predictions with a proof-of-concept demonstration of a time-switched nonlocal TL MTM, observing a vertical transition in the dispersion diagram induced by abrupt time switching. Our results provide key physical insights into the behavior of nonlocal MTMs, establish a versatile platform to investigate the interplay of frequency dispersion, spatial dispersion and time modulation, and lay a general foundation for the design of more advanced nonlocal and time-varying electromagnetic and photonic systems.

Colloidal gels, like many other soft and disordered solids derive their mechanical properties not only from the strength of interparticle attraction but also from the symmetry of the forces that constrain particle motion. Although noncentral interactions are known to profoundly alter rigidity and elasticity, they are typically introduced through particle anisotropy, surface roughness, or patchy interactions, obscuring their independent role. Here, we demonstrate a minimal and geometry-preserving route to emergent noncentral forces in colloidal gels by reducing the density of surface-grafted polymer brushes. At low brush density, partial brush interpenetration introduces an effective angular bending rigidity at particle contacts, despite fully isotropic particle geometry. This emergent constraint suppresses local densification, stabilizes low-coordination networks, and produces highly ramified gel structures with enhanced elasticity. Combining experiments, simulations, and mean-field theory, we show that these noncentral constraints reorganize structure and mechanics across length scales, shifting gelation boundaries and increasing the elastic modulus by nearly a factor of 3. Our results establish surface brush density as a generic control parameter for programming interaction symmetry in soft particulate matter, with implications for rigidity, percolation, and mechanical design in disordered systems.

Multiple scattering limits optical imaging in thick biological samples by scrambling sample-specific information. Physics-based inverse-scattering methods aim to computationally recover this information, often using non-convex optimization to reconstruct the scatter-corrected sample. However, this non-convexity can lead to inaccurate reconstructions, especially in highly scattering samples. Here, we show that various implementation strategies for even the same inverse-scattering method significantly affect reconstruction quality. We demonstrate this using multi-slice beam propagation (MSBP), a relatively simple nonconvex inverse-scattering method that reconstructs a scattering sample's 3D refractive-index (RI). By systematically conducting MSBP-based inverse-scattering on both phantoms and biological samples, we showed that an amplitude-only cost function in the inverse-solver, combined with angular and defocus diversity in the scattering measurements, enabled high-quality, fully-volumetric RI imaging. This approach achieved subcellular resolution and label-free 3D contrast across diverse, multiple-scattering samples. These results lay the groundwork for robust use of inverse-scattering techniques to achieve biologically interpretable 3D imaging in increasingly thick, multicellular samples, introducing a new paradigm for deep-tissue computational imaging.

Metal halide perovskites (MHPs) have transformed the landscape of photovoltaics and optoelectronics due to their remarkable optical and electronic properties. Although lead (Pb)based halide perovskites have shown exceptional power conversion efficiency (PCE) and superior photoluminescence (PL) properties, environmental concerns about Pb toxicity have prompted research into Pb-free alternatives. Fortunately, among the Pb-free candidates, tin (Sn)-based halide perovskites (Sn-HPs) have emerged as potential candidates. Sn-HPs have an optimal bandgap, high charge carrier mobility, and long-lived hot carriers. However, the inherent instability of Sn 2+ , which readily oxidizes to Sn 4+ , poses significant challenges, leading to unintentional p-type doping, thereby degrading PSCs performance. Despite these challenges, recent progress in the stabilization of Sn²⁺, improvement of thin-film quality, and advancement in device engineering has significantly enhanced the performance and reliability of Sn-HPs. In this review, we systematically discuss the fundamental photophysical properties and strategies to mitigate intrinsic defects in tin halide perovskites (Sn-HPs) across various structural modifications. Furthermore, advanced spectroscopic techniques, such as timeresolved spectroscopy, ultrafast transient absorption, and hot-carrier dynamics, enhance understanding of fundamental carrier dynamics and the potential of hot-carrier-based optoelectronic devices. Subsequently, we present recent advancements in achieving stable and efficient performance in LEDs, photodetectors, and photovoltaic technology, and provide perspectives on future developments.