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Semiconductor excitations can hybridize with cavity photons to form exciton-polaritons (EPs) with remarkable properties, including light-like energy flow combined with matter-like interactions. To fully harness these properties, EPs must retain ballistic, coherent transport despite matter-mediated interactions with lattice phonons. Here we develop a nonlinear momentum-resolved optical approach that directly images EPs in real space on femtosecond scales in a range of polaritonic architectures. We focus our analysis on EP propagation in layered halide perovskite microcavities. We reveal that EP–phonon interactions lead to a large renormalization of EP velocities at high excitonic fractions at room temperature. Despite these strong EP–phonon interactions, ballistic transport is maintained for up to half-exciton EPs, in agreement with quantum simulations of dynamic disorder shielding through light-matter hybridization. Above 50% excitonic character, rapid decoherence leads to diffusive transport. Our work provides a general framework to precisely balance EP coherence, velocity, and nonlinear interactions. Exciton-polaritons are part-light part-matter states in semiconductors. Here the authors leverage momentum-resolved optical microscopy to image ballistic and diffusive propagation of exciton-polaritons on femtosecond scales.

The ability of energy carriers to move between atoms and molecules underlies biochemical and material function. Understanding and controlling energy flow, however, requires observing it on ultrasmall and ultrafast spatio-temporal scales, where energetic and structural roadblocks dictate the fate of energy carriers. Here, we developed a non-invasive optical scheme that leverages non-resonant interferometric scattering to track tiny changes in material polarizability created by energy carriers. We thus map evolving energy carrier distributions in four dimensions of spacetime with few-nanometre lateral precision and directly correlate them with material morphology. We visualize exciton, charge and heat transport in polyacene, silicon and perovskite semiconductors and elucidate how disorder affects energy flow in three dimensions. For example, we show that morphological boundaries in polycrystalline metal halide perovskites possess lateral- and depth-dependent resistivities, blocking lateral transport for surface but not bulk carriers. We also reveal strategies for interpreting energy transport in disordered environments that will direct the design of defect-tolerant materials for the semiconductor industry of tomorrow. A stroboscopic scattering microscopy approach is developed to image the evolution of carrier distributions in three dimensions and with sub-nanosecond resolution while the carriers propagate in organic and inorganic films.

Cavity exciton-polaritons exhibit ballistic transport and can achieve 100 μ m in one picosecond. This ballistic transport significantly enhances mobility compared to that of bare excitons, which often move diffusively and become the bottleneck for energy conversion and transfer devices. Despite being robustly reproduced in experiments and simulations, there is no microscopic theory available for describing the group velocity v g of polariton transport and its renormalization. In this work, we derive an analytic expression for v g renormalization. The theory suggests the v g renormalization is caused by phonon-mediated transitions between the lower polariton (LP) states and the dark states. The theory predicts that the renormalization magnitude depends on both exciton-phonon coupling strength and temperature, which are in quantitative agreement with numerical quantum dynamics simulations. Our results provide theoretical insights and a predictive analytical theory for understanding cavity-enhanced exciton-polariton transport. The authors advance the foundations of exciton-polariton transport based on a field-theoretical approach. This provides microscopic insight on the experimentally observed group velocity renormalization effect.

Exciton polaritons are quasiparticles of photons coupled strongly to bound electron-hole pairs, manifesting as an anti-crossing light dispersion near an exciton resonance. Highly anisotropic semiconductors with opposite-signed permittivities along different crystal axes are predicted to host exotic modes inside the anti-crossing called hyperbolic exciton polaritons (HEPs), which confine light subdiffractionally with enhanced density of states. Here, we show observational evidence of steady-state HEPs in the van der Waals magnet chromium sulfide bromide (CrSBr) using a cryogenic near-infrared near-field microscope. At low temperatures, in the magnetically-ordered state, anisotropic exciton resonances sharpen, driving the permittivity negative along one crystal axis and enabling HEP propagation. We characterize HEP momentum and losses in CrSBr, also demonstrating coupling to excitonic sidebands and enhancement by magnetic order: which boosts exciton spectral weight via wavefunction delocalization. Our findings open new pathways to nanoscale manipulation of excitons and light, including routes to magnetic, nonlocal, and quantum polaritonics. Hyperbolic exciton polaritons (HEPs) are anisotropic light-matter excitations with promising applications, but their steady-state observation is challenging. Here, the authors report experimental evidence of HEPs in a van der Waals magnet, CrSBr, via cryogenic infrared near-field microscopy.

The ability to produce large-grain REBCO (RE=Y, Rare Earth) bulk superconductors by melt texturing growth has been improved and refined significantly over the last 20 years. Magnetic bearings, transportation systems, and scientific instrumentation are becoming major innovations of HTS bulk materials. Large grain production is dominated by cold top-seeding melt growth (TSMG). For material optimizing we demonstrate strictly application-oriented fabrication close to the final geometry and thus reducing mechanical machining and assembling work. YBCO hollow cylinder design for journal bearings with radial c axes orientation are obtained by radial-seeding geometry (RSMG). YBCO ring tiles up 120 mm show a perfect cylinder geometry with in-wall a, b orientation and radial c axes. We report improved electric and mechanical bulk properties and demonstrate great production effectiveness. For achieving high field permanent magnets up to 10 T we compare YBCO bulk and ring geometry. Top/bottom double seeded melt growth (DSMG) grain samples provide better magnetic flux trapping capability and show more homogenous properties.

Electron transfer (ET) from donor to acceptor is often mediated by nuclear-electronic (vibronic) interactions in molecular bridges. Using an ultrafast electronic-vibrationalvibrational pulse-sequence, we demonstrate how the outcome of light-induced ET can be radically altered by mode-specific infrared (IR) excitation of vibrations that are coupled to the ET pathway. Picosecond narrow-band IR excitation of high-frequency bridge vibrations in an electronically excited covalent trans-acetylide platinum(II) donor-bridge-acceptor system in solution alters both the dynamics and the yields of competing ET pathways, completely switching a charge separation pathway off. These results offer a step toward quantum control of chemical reactivity by IR excitation.

The recent discoveries of two-dimensional (2D) magnets 1 – 6 and their stacking into van der Waals structures 7 – 11 have expanded the horizon of 2D phenomena. One exciting application is to exploit coherent magnons 12 as energy-efficient information carriers in spintronics and magnonics 13 , 14 or as interconnects in hybrid quantum systems 15 – 17 . A particular opportunity arises when a 2D magnet is also a semiconductor, as reported recently for CrSBr (refs. 18 – 20 ) and NiPS 3 (refs. 21 – 23 ) that feature both tightly bound excitons with a large oscillator strength and potentially long-lived coherent magnons owing to the bandgap and spatial confinement. Although magnons and excitons are energetically mismatched by orders of magnitude, their coupling can lead to efficient optical access to spin information. Here we report strong magnon–exciton coupling in the 2D A-type antiferromagnetic semiconductor CrSBr. Coherent magnons launched by above-gap excitation modulate the exciton energies. Time-resolved exciton sensing reveals magnons that can coherently travel beyond seven micrometres, with a coherence time of above five nanoseconds. We observe these exciton-coupled coherent magnons in both even and odd numbers of layers, with and without compensated magnetization, down to the bilayer limit. Given the versatility of van der Waals heterostructures, these coherent 2D magnons may be a basis for optically accessible spintronics, magnonics and quantum interconnects. Excitons in the electronvolts range are found to couple strongly to coherent magnons in hundreds of microelectronvolts in an atomically thin two-dimensional antiferromagnetic semiconductor.

Nuclear–electronic (vibronic) coupling is increasingly recognized as a mechanism of major importance in controlling the light-induced function of molecular systems. It was recently shown that infrared light excitation of intramolecular vibrations can radically change the efficiency of electron transfer, a fundamental chemical process. We now extend and generalize the understanding of this phenomenon by probing and perturbing vibronic coupling in several molecules in solution. In the experiments an ultrafast electronic–vibrational pulse sequence is applied to a range of donor–bridge–acceptor Pt( II ) trans -acetylide assemblies, for which infrared excitation of selected bridge vibrations during ultraviolet-initiated charge separation alters the yields of light-induced product states. The experiments, augmented by quantum chemical calculations, reveal a complex combination of vibronic mechanisms responsible for the observed changes in electron transfer rates and pathways. The study raises new fundamental questions about the function of vibrational processes immediately following charge transfer photoexcitation, and highlights the molecular features necessary for external vibronic control of excited-state processes. The ultrafast and mode-specific infrared excitation of several donor–bridge–acceptor (DBA) assemblies in solution has been shown to modulate their light-induced electron transfer properties. New insights are afforded into the role of vibrational processes immediately following light absorption in charge-transfer molecules and a recipe for efficient ‘vibrational control’ of electron transfer is proposed.

Ultrafast electron transfer in condensed-phase molecular systems is often strongly coupled to intramolecular vibrations that can promote, suppress and direct electronic processes. Recent experiments exploring this phenomenon proved that light-induced electron transfer can be strongly modulated by vibrational excitation, suggesting a new avenue for active control over molecular function. Here, we achieve the first example of such explicit vibrational control through judicious design of a Pt( II )-acetylide charge-transfer donor–bridge–acceptor–bridge–donor ‘fork’ system: asymmetric 13 C isotopic labelling of one of the two –C≡C– bridges makes the two parallel and otherwise identical donor→acceptor electron-transfer pathways structurally distinct, enabling independent vibrational perturbation of either. Applying an ultrafast UV pump (excitation)–IR pump (perturbation)–IR probe (monitoring) pulse sequence, we show that the pathway that is vibrationally perturbed during UV-induced electron transfer is dramatically slowed down compared to its unperturbed counterpart. One can thus choose the dominant electron transfer pathway. The findings deliver a new opportunity for precise perturbative control of electronic energy propagation in molecular devices. With recent and improved understanding of how nuclear and electronic degrees of freedom can interact with each other comes the opportunity to directly control electronic processes. Now it has been shown that ultrafast vibrational excitation can direct light-induced intramolecular electron transfer along a specific path.

Globally, millions of wild birds are admitted to rehabilitation centres each year. We analysed data on wild bird admissions at an urban rehabilitation centre in Berlin, Germany, collected over 20 years (2005–2024), aiming to (a) characterise admission causes and demographics, (b) investigate the rehabilitation duration and release probability across admission causes and systematic bird groups, and (c) assess post-release survival as a proxy for rehabilitation success. Longer rehabilitation durations were generally associated with orphaned birds and those in poor condition or who had had an infection. Orphans and birds with undetermined admission causes were most likely to be released. Birds that were admitted in poor condition were least likely to be released, which was particularly the case among Passerines. The monitoring of post-release survival through ring recovery data revealed higher recovery rates for larger birds but no informative value on post-release survival across species; thus, it did not represent an ideal measure of rehabilitation success in terms of the original objective. We conclude that the extent, outcome, and success of wild bird rehabilitation may depend on the initial cause of admission and may differ between bird groups. Advanced measures to assess post-release survival should be considered to allocate the limited resources and the conservation efforts of wild bird rehabilitation centres to birds of species and/or admission causes best suited to undergoing rehabilitation.