Nature Materials

We present a unified derivation of the Breit-Wheeler pair production process as the topological redistribution of the magnetic field energy between two photon lemniscatas and two electron/positron hopfions. In the Conjugate Photonic Model (CPM), each photon is a two-leaf lemniscatic field structure with , where the anticlockwise lobe carries of field energy and the clockwise lobe carries in exact bilateral symmetry. At the Breit-Wheeler threshold , the combined anticlockwise lobes of both photons have sufficient field energy to satisfy the hopfion confinement criterion:. The two anticlockwise lobes merge and close topologically into a hopfion (electron), while the two clockwise lobes merge into a hopfion (positron). The field of the photons is thus literally redistributed into the fields of the electron and positron. We support this derivation with three recent experimental anchors: nondiffracting supertoroidal pulses (NDSTPs) demonstrate that propagation-robust toroidal field configurations with skyrmionic topology exist as exact Maxwell solutions (Shen et al. 2024); optical skyrmions confirm that topological quasiparticles with definite Hopf-like numbers appear in free EM fields (Shen et al. 2023); and topological photonics establishes that photonic states characterised by non-trivial topology of EM fields are a broad physical reality (Khanikaev and Alù 2024). The energy threshold, the conservation of Hopf number, the massenergy identity , and the polarisation dependence of pair production rate are all derived from a single geometric principle: the field of the photon lemniscata becomes the field of the pair hopfions. γγ → e

We study the effect of the Dzyaloshinskii-Moriya interaction (DMI) on current-induced magnetic switching of a perpendicularly magnetized heavy-metal/ferromagnet/oxide trilayer both experimentally and through micromagnetic simulations. We report the generation of stable helical magnetization stripes for a sufficiently large DMI strength in the switching region, giving rise to intermediate states in the magnetization confirming the essential role of the DMI on switching processes. We compare the simulation and experimental results to a macrospin model, showing the need for a micromagnetic approach. The influence of the temperature on the switching is also discussed.

Microfluidic systems allow (bio)chemical processes to be miniaturized with the benefit of shorter time-to-result, parallelism, reduced sample consumption, laminar flow, and increased control and efficiency. However, such miniaturization inherently limits the size of the solid objects that can be processed and entails new challenges such as the interfacing of macroscopic samples with microscopic conduits. Here, we report a microfluidic probe (MFP) that overcomes these problems by combining the concepts of 'microfluidics' and of 'scanning probes'. Here, liquid boundaries formed by hydrodynamic forces underneath the MFP confine a flow of processing solution and replace the solid walls of closed microchannels. The MFP is therefore mobile and can be used to process large surfaces and objects by scanning across them. We illustrate the versatility of this concept with several examples including protein microarraying, complex gradient-formation, multiphase laminar-flow patterning, erasing, localized staining of cells and the contact-free detachment of a single cell. Many constraints imposed by the monolithic construction of microfluidic channels can now be circumvented using an MFP, opening up new avenues for microfluidic processing.

An amorphous-silicon thin-film transistor (TFT) process with a 180 • C maximum temperature using plasmaenhanced chemical vapor deposition has been developed on both novel clear polymer and glass substrates. The gate leakage current, threshold voltage, mobility, and on/off ratio of the TFTs are comparable with those of standard TFTs on glass with deposition temperature of 300 • C-350 • C. Active-matrix pixel circuits for organic light-emitting displays (LEDs) on both glass and clear plastic substrates were fabricated with these TFTs. Leakage current in the switching TFT is low enough to allow data storage for video graphics array timings. The pixels provide suitable drive current for bright displays at a modest drive voltage. Test active matrices with integrated polymer LEDs on glass showed good pixel uniformity, behaved electrically as expected for the TFT characteristics, and were as bright as 1500 cd/m 2 .

The potential profile and the energy level offset of core/shell heterostructured nanocrystals (h-NCs) determine the photophysical properties and the charge transport characteristics of h-NC solids. However, limited material choices for heavy metal-free III-V/II-VI h-NCs pose challenges in comprehensive control of the potential profile. Herein, we present an unprecedented approach to such control by steering dipole moments at the interface of III-V/II-VI h-NCs. The controllable heterovalency at the interface is responsible for interfacial dipole moments that result in the vacuum-level shift, providing an additional knob for the control of optical and electrical characteristics of h-NCs. We capitalize on the atomic precision with which to synthesize h-NCs by correlating interfacial dipole moments to photochemical stability and optoelectronic performance of resulting h-NCs.

We report on large-scale simulations of intrachain exciton dynamics in poly(para-phenylene vinylene). Our coarse-grained model describes Frenkel exciton coupling to both fast, quantized CC bond vibrations and slow, classical torsional modes. We also incorporate systembath interactions. The dynamics are simulated using the Time Evolution Block Decimation method, which avoids the failures of the Ehrenfest approximation to describe decoherence processes and nonadiabatic interstate conversion. System-bath interactions are modeled using quantum trajectories and Lindblad quantum jump operators. We find that following photoexcitation, the quantum mechanical entanglement of the exciton and CC bond phonons causes exciton-site decoherence. Next, system-bath interactions cause the stochastic collapse of highenergy delocalized excitons onto chromophores. Finally, torsional relaxation causes additional exciton-density localization. We relate these dynamical processes to the predicted fluorescence depolarization and extract the timescales corresponding to them.

A study has been perfomed on the superconducting critical current density J_{c} flowing across low angle grain boundaries in epitaxial thin films of YBa{2}Cu{3}O{7-d} (YBCO). The materials studied were dual grain boundary rings deposited on SrTiO{3} and containing 2, 3, 5 and 7 degree tilt boundaries. The current density in self-field was determined by magnetometric methods at temperatures from 5 K to T_c. We conclude that at the higher temperatures of coated conductor applications, there is limited potential for improving J_{c} by reducing the grain boundary angle below about 3 degrees.

Recent large-scale computer simulations suggest that it may be possible to create a new class of soft solids, called 'bijels', by stabilizing and arresting the bicontinuous interface in a binary liquid demixing via spinodal decomposition using particles that are neutrally wetted by both liquids . The interfacial layer of particles is expected to be semi-permeable [2], hence, if realised, these new materials would have many potential applications, e.g. as microreaction media. However, the creation of bijels in the laboratory faces serious obstacles . In general, fast quench rates are necessary to bypass nucleation, so that only samples with limited thickness can be produced, which destroys the threedimensionality of the putative bicontinuous network. Moreover, even a small degree of unequal wettability of the particles by the two liquids can lead to ill-characterised, 'lumpy' interfacial layers and therefore irreproducible material properties. Here we report a reproducible protocol for creating three-dimensional samples of bijel in which the interfaces are stabilized by essentially a single layer of particles. We demonstrate how to tune the mean interfacial separation in these bijels, and show that mechanically, they indeed behave as soft solids. Thermally induced demixing provides a route to creating varied arrangements of fluid-fluid interfaces. On a mean-field level two kinetic path-

The emerging field of spintronics explores the many possibilities offered by the prospect of using the spin of the electrons for fast, nanosized electronic devices. The effect of magnetization acting on a current is the essence of giant or tunnel magnetoresistance. Although such spintronics effects already find technological applications, much of the underlying physics remains to be explored. The aim of this article is to demonstrate the importance of spin mixing in metallic nanostructures. Here we show that magnetic clusters embedded in a metallic matrix exhibit a giant magnetic response of more than 500% at low temperature, using a recently developed thermoelectric measurement. This method eliminates the dominating resistivity component of the magnetic response and thus reveals an intrinsic spin-dependent process: the conduction-electron spin precession about the exchange field as the electron crosses the clusters, giving rise to a spin-mixing mechanism with strong field dependence.

When a granular material such as sand is mixed with a certain amount of liquid, the surface tension of the latter bestows considerable stiffness to the material, which enables, for example, sand castles to be sculpted . The geometry of the liquid interface within the granular pile is of extraordinary complexity and strongly varies with the liquid content 5-7 . Surprisingly, the mechanical properties of the pile are largely independent of the amount of liquid 2,8-13 over a wide range . We resolve this puzzle with the help of X-ray microtomography, showing that the remarkable insensitivity of the mechanical properties to the liquid content is due to the particular organization of the liquid in the pile into open structures. For spherical grains, a simple geometric rule is established, which relates the macroscopic properties to the internal liquid morphologies. We present evidence that this concept is also valid for systems with nonspherical grains. Hence, our results provide new insight towards understanding the complex physics of a large variety of wet granular systems including land slides, as well as mixing and agglomeration problems. It is a familiar experience at the beach that sand makes a mouldable material almost irrespective of the amount of water added: no-one needs a recipe to build a sand castle. Assemblies of wet glass spheres show the same basic phenomena as wet sand, and thus are widely used model systems . Figure shows data for three characteristic mechanical parameters of a wet pile of glass beads. The tensile strength, the yield stress and the critical acceleration at which fluidization sets in are plotted as a function of liquid content, W , in the range 0 < W ≤ 0.15. The latter is defined as the liquid volume divided by the total sample volume. Accordingly, W = 0.15 is equivalent to about 35% of the available pore space. Clearly, none of the three quantities depends significantly on the liquid saturation. Within the experimental uncertainties, all of the data points are consistent with the horizontal dashed line, which serves as a guide to the eye. The only exception is the sharp rise at very small W , where the transition from the dry state to the wetted state (capillary bridges) takes place . This results from filling the crevices and roughness on the bead surfaces with liquid and shall not concern us here any further. The fact that the mechanical properties are largely unaffected by the liquid content in the remaining, wide range of W corroborates the experience at the beach, and will be the subject of this article.

Water interaction with mineral surfaces is a complex living system decisive for any photocatalytic process. Resolving the atomistic structure of mineral-water interfaces is thus crucial for understanding these processes. Fibrous rutile TiO 2 , grown hydrothermally on twinned rutile seeds under acidic conditions, is studied in terms of interface translation, atomic structure, and surface chemistry in the presence of water, by means of advanced microscopy and spectroscopy methods combined with structure modeling and density functional theory calculations. It is shown that fibers while staying in stable separation during their growth, adopt a special crystallographic registry that is controlled by repulsion forces between fully hydroxylated and protonated (110) surfaces. During relaxation, a turbulent proton transfer and cracking of O─H bonds is observed, generating a strong acidic character via proton jump from bridge ─OH b to terminal ─OH t groups, and spontaneous dissociation of interfacial water via a transient protonation of the ─OH t groups. It is shown, that this specific interface structure can be implemented to induce acidic response in an initially neutral medium when re-immersed. This is thought to be the first demonstration of quantum-confined mineral-water interface, capable of memorizing its past and conveying its structurally encoded properties into a new environment.

Conductive Metal-Organic Frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, like their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, we describe a possible origin for the underlying mechanism of this phenomenon in ultrathin films (~30 nm) of Cu-CAT-1.

Conductive Metal-Organic Frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, like their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, we describe a possible origin for the underlying mechanism of this phenomenon in ultrathin films (~30 nm) of Cu-CAT-1.

Hybridization of an organic Frenkel exciton (layer-by-layer TDBC) and an inorganic Wannier-Mott exciton (WS2 monolayer) results in the formation of a multi-polaritonic system. Such a hybrid platform offers an excellent way of engineering the emission through the coupled states. This article demonstrates the mapping of dispersion characteristics of multi-polaritonic emission using excitation and momentum resolved, Fourier-plane micro-spectroscopy. Further, the contribution of photon fractions is correlated to the emission of the polaritonic branches. For example, an increase in the photon fraction of the middle polaritonic state is observed at certain momenta in the Fourier space, thereby amplifying the emission population density. The competition between the middle and lower polaritonic states is tested at various cavity detuning conditions and found to be in accordance with the modeling. This work has potential implications and helps to design future-generation optoelectronic and photonic devices.

This paper presents a formal investigation into the superconducting phase of bilayer nickelate (La3Ni2O7) utilizing the Hamiltonian Coherence Threshold (HCT) framework. Under high-pressure conditions of approximately 30 GPa, the system is audited against the HCT Three-Strike criteria, where the resonance of the Ni 3dz2 orbitals is identified as the primary driver for macroscopic coherence. The activation threshold (TH) is established at 80 K, marking the initiation of a first-order phase-lock that is structurally grounded by the Z = 6 octahedral coordination of the nickel-oxygen bilayers. This structural determinism results in a calculated stabilization floor (Tc,down) of 62.7 K, defining a characteristic 17.3 K thermal split between the onset of activation and the achievement of zero resistance. The precise alignment between the theoretical scattering constant ( 0.784) and experimental benchmarks reinforces the status of the HCT model as a universal axiomatic standard, demonstrating that structural coordination is the fundamental architect of high-temperature superconductivity in nickelate systems.

Molybdenum disulfide (MoS 2) is widely used in energy harvesting devices due to its high carrier mobility and semiconductor properties. However, the preparation of high-quality MoS 2 still faces significant challenges. In this work, we present a one-step chemical vapor deposition method for the preparation of large-size MoS 2 nanosheets with an orientation rate of over 70%. The one-step preparation method is more cost-effective and time-efficient compared to conventional techniques. The aligned MoS 2 nanosheets demonstrate a significant capacity for charge transfer in triboelectric devices. Herein, we propose a concept of MoS 2 as the charge transport layer for nanogenerator arrays for hybrid energy harvesting and high-performance direct output. Furthermore, the current density of the device exceeds 10 A/m 2 under ultrasonic excitation. Consequently, this finding is anticipated to offer new insights into applications such as mechanical energy conversion and MoS 2 charge transport.

In this work, we present a study on the synthesis and characterization of Ni-Pt alloy nanoparticles, integrating advanced experimental techniques with theoretical modeling to gain a detailed understanding of their morphology and structural stability. The nanoparticles were synthesized through a precisely controlled chemical approach designed to promote alloy homogeneity. High-resolution transmission electron microscopy (TEM) allowed direct observation of particle morphology, lattice arrangement, and structural diversity, revealing a range of shapes rather than a single uniform geometry. Among the observed structures, the Ni 3 Pt phase was the most prominent, appearing in both octahedral and cubic geometries with well-defined lattice fringes. Molecular Dynamics simulations confirmed the stability of these structures, reproduced their crystallographic features, and predicted a high melting point of approximately 2250 K. These combined results provide valuable insights into the relationship between composition, structure, and stability, highlighting potential applications in several fields such as catalysis, energy conversion, and advanced functional nanotechnology.

Kirchhoff's 1859 blackbody universality claim asserts that cavity radiation at thermal equilibrium is independent of wall material.

His own definition, however, requires a physical surface: absorption demands a material interface. Kirchhoff erased the wall from his mathematics while his physics required it.

This internal contradiction is the foundational flaw from which Planck's 1900 derivation of h inherited its unexplained postulates (Theorem 176, PUH).

This paper establishes that within the Photonic Universe Hypothesis, the physically unique universal blackbody surface is the Planck Shell-the level set of the degree-30 E8 Casimir invariant C 8 (φ) = c*, the topological boundary separating Phase I (crystallized E8 lattice) from Phase II (healing geometry).

The Planck Shell is simultaneously a perfect absorber (no Hamiltonian trajectory crosses it, by Theorem 156) and a perfect emitter (the full E8 lattice mode spectrum is activated at λ = λ*, by Theorem 175).

It is the only surface in nature at which the E8 lattice tension λ reaches the Snap threshold λ* exactly.

All other blackbody sources-stellar photospheres, laboratory cavities, metallic surfaces-are partial realizations of the Planck Shell: physical systems in which the E8 lattice tension approaches but does not reach λ*.

The continuous blackbody spectrum is not a universal law of empty space. It is the resonance profile of the E8 Phase I lattice, maximally activated at the Planck Shell boundary.

The Sun's blackbody emission is produced by metallic hydrogen under gravitational compression driving the local E8 lattice tension toward λ*.

Three falsifiable predictions follow.

Electronic structure and electron-phonon coupling of carbon clathrates C 40 , C 34 , and C 46 doped with interstitial halogen atoms ͑fluorine, iodine͒ in the fullerenic cages of the host, have been investigated from first principles. It turns out that, while in C 40 and C 46 the halogen is only partially reduced, in FC 34 an electron is transferred to the guest ion by injecting holes in the valence band of the host. The calculated electron-phonon coupling constant is as large as = 0.85. We propose that halogen-doped carbon clathrates might represent another form of tetrahedral carbon, in addition to the recently found B-doped diamond, suitable to turn superconductive at high temperature ͑T c ϳ 77 K from McMillan formula͒.