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Lasers based on Landau levels, which should offer wide wavelength tunability, including across the elusive THz range, are a step closer to reality with a demonstration showing how to suppress the main loss mechanism.

Photoexciting molecules provides insights into their different degrees of freedom if the ultrafast electron and nuclei motion can be properly analysed. To this end, McFarland et al.use X-ray pump-probe techniques to show that Auger spectra can unveil information on nuclear relaxation in molecules.

Radiative Auger is a process that leads to a red-shift of the optical emission of an atom or a charged solid-state quantum emitter. Here, the authors realize the inverse process by optically driving the radiative Auger transition of a short-lived electronic state in a semiconductor quantum dot.

Self-referenced attosecond streaking enables in situ measurements of Auger emission in atomic neon excited by femtosecond pulses from an X-ray free-electron laser with subfemtosecond time resolution and despite the jitter inherent to X-ray free-electron lasers.

Intermolecular Coulombic decay transfers excess energy to neighbouring molecules, which then lose a low-energy (and, hence, genotoxic) electron; here the process is experimentally confirmed to be site-selective and highly efficient, possibly enabling more targeted radiation therapy.

In a radiative Auger process, an excited electron relaxes by concomitant emission of a redshifted photon and energy transfer to another electron. Measuring radiative Auger processes in a quantum dot with single-photon resolution enables determination of the energy of single-electron levels as well as their lifetimes.

Slow electrons, which cause radiation damage, are efficiently produced by interatomic neutralization processes. Here, the authors show experimental evidence for the efficient neutralization of the ionic states produced in Auger decay, using large neon–krypton clusters as a prototype system.

Charge transfer is facilitated in molecular systems through orbital coupling. Here the authors use core-hole-clock spectroscopy to show that electron transfer from an argon atom caged in a fullerene can be up to two orders of magnitude faster than for the isolated atom.

Owing to their layered nature, transition metal dichalcogenides possess an anisotropic electronic structure whose impact on carrier dynamics is not fully known. Here, the authors use X-ray spectroscopy to unveil the electronic coupling and attosecond dynamics in SnS₂, a prototypical van der Waals layered crystal.

Harvesting excess energy from above-band gap photons could lead to solar cells which exceed conventional efficiency limits. Liet al., study hot carrier cooling in hybrid perovskite materials with reduced dimensionality using transient absorption spectroscopy and demonstrate efficient hot-electron extraction in such systems.

Harvesting excess energy from above-bandgap photons can break solar cells’ conventional efficiency limits. Using transient spectroscopy, modelling and ab-initio calculations, Fu et al., unravel the interplay between hot phonon bottleneck and Auger heating effects on hot-carrier cooling in halide perovskites.

Molecular core levels are localized around a single atomic site, but for indistinguishable atoms, photoionised core-holes can either be seen as localized or delocalized. Using a prototypical symmetric system, CS₂, Guillemin et al. show that these states can be disentangled by fragmentation dynamics.

Understanding the dynamics of molecules exposed to intense X-ray beams is crucial to ongoing efforts in biomolecular imaging with free-electron lasers. Here, the authors study C₆₀molecules interacting with femtosecond X-ray free-electron laser pulses and present a model based on classical and quantum physics.

With the start-up of the first X-ray free-electron laser, a new era has begun in dynamical studies of atoms. Here the facility is used to study the fundamental nature of the electronic response in free neon atoms. During a single X-ray pulse, they sequentially eject all their ten electrons to produce fully stripped neon. The authors explain this electron-stripping in a straightforward model, auguring favourably for further studies of interactions of X-rays with more complex systems.

Compositionally complex alloys have attracted significant attention recently, but the role of electronic correlations in these materials is unknown. Redka et al. study the CrMnFeCoNi alloy using a combination of experimental and theoretical techniques, revealing strong correlation effects far from the Fermi edge.

A very high-energy muon observed by the KM3NeT experiment in the Mediterranean Sea is evidence for the interaction of an exceptionally high-energy neutrino of cosmic origin.  

Two-color X-ray pulses with controlled time delay allow exciting one site of a molecule and then probing a different site of the same molecule with femtosecond resolution. Here, the authors use this hetero-site pump-probe technique to study charge redistribution and dissociation of the xenon difluoride molecule.

The efficiency of lead-halide perovskite photovoltaics is related to the tolerance of their band-edge charge-carriers to point defects. Here, the authors show that this tolerance can be extended to hot carriers depending on the defect energy level.

Solution-processable CdS ‘bulk’ nanocrystals show efficient on-chip lasing under quasi-continuous-wave conditions with excellent beam quality and pump thresholds.

A time-resolved observation of electron tunnelling and the short-lived electronic states that subsequently appear is useful as a new approach to obtain insights in multi-electron dynamics inside atoms and molecules. This technique of 'attosecond tunnelling' is applied to study the cascade of electronic transitions that occur in xenon atoms as a result of their ionization.

The authors report upconversion in few-layer transition metal dichalcogenides, and attribute it to a resonant exciton-exciton annihilation involving a pair of dark excitons with opposite momenta, followed by the spontaneous emission of upconverted bright excitons.

Electrons in atoms exhibit many-body collective behaviours that can be studied by highbrightness X-rays from FELs. Here, the authors examine two-photon above threshold ionization of xenon and find that nonlinearities in the response uncover that more than one state underpins the 4dgiant resonance.

X-ray free electron lasers provide high photon flux to explore single particle diffraction imaging of biological samples. Here the authors present dynamic electronic structure calculations and benchmark them to single-particle XFEL diffraction data of sucrose clusters to predict optimal single-shot imaging conditions.

Two-dimensional massive and massless Dirac fermions in HgTe/CdHgTe quantum wells yield terahertz Landau emission. The emission frequency is continuously tunable with magnetic field or carrier concentration, over the range from 0.5 to 3 THz.

Matter at extremely high density and pressure behaves differently than at ambient conditions. Here the authors use first-principles calculations to show the existence of interspecies radiative and dipole-forbidden transitions in warm and superdense plasma mixture of iron and zinc.

Bennu comprises components of intra- and extra-Solar System origins. The parent bodies of Bennu, Ryugu and CI chondrites likely formed from a shared but heterogeneous reservoir in the outer parts of the solar protoplanetary disk.

During the Fischer-Tropsch catalytic reaction, alkanes are synthesized from carbon monoxide and hydrogen at high pressure and temperature. Now it is shown using scanning tunnelling imaging of a cobalt surface during reaction that linear alkane product molecules of a specific length self-assemble on terraces, facilitating the desorption of new product molecules created at step sites.

Hybrid perovskite semiconductors are promising for wavelength-tunable laser diodes but their behavior under intense electrical excitation remains unexplored. Kim et al. investigate perovskite light emitting diodes at current densities nearing 1 kA cm⁻² and suggest that a laser diode is within reach.

Understanding the dynamics of cuprates following photoexcitation can provide insights into the complex coupling mechanisms that underlie their exotic equilibrium behaviour. Here the authors use pump-probe reflection spectroscopy to investigate the nonequilibrium spin dynamics of Mott-insulating Nd₂CuO₄.

Hybrid halide perovskites have demonstrated promising performance as solar cells. It is now reported that these solution-processed materials are also suited to lasing applications, because of the high optical gain and stable amplified spontaneous emission they show in the visible spectral range.

Strategies to systematically tune CO₂ electroreduction to multicarbon products are of high interests. Here the authors report electron withdrawing functional group alters the reaction pathway towards C₂₊ products by adjusting the oxidation state of surface copper.

An ultrafast visible band in the photoluminescence spectrum of silicon nanocrystals increases in intensity and shifts to longer wavelengths as the size of the nanocrystals decreases.

X-ray pump–probe experiments reveal that the molecular structure of C₆₀ molecules substantially delays their fragmentation following photoionization. This may help to understand X-ray laser-induced radiation damage on molecules.

Solid electrolyte interphase (SEI) formation on Li-ion battery anodes is critical for long-term performance. Here, the authors use operando soft X-ray absorption spectroscopy in total electron yield mode to resolve the chemical evolution of the SEI during electrochemical formation on silicon anodes.

Many photo-induced processes such as photosynthesis occur in organic molecules, but their femtosecond excited-state dynamics are difficult to track. Here, the authors exploit the element and site selectivity of soft X-ray absorption to sensitively follow the ultrafast ππ*/nπ* electronic relaxation of hetero-organic molecules.

Understanding the chemistry of perovskite precursor solutions enables improved film optoelectronic properties, allowing the fabrication of multijunction solar cells achieving power conversion efficiencies beyond the radiative limit of single-junction cells.

To understand enzymatic redox reaction mechanisms, it is important to investigate the redox behavior at the metal centers. This Protocol describes metalloenzyme attachment to electrodes and how to perform X-ray absorption spectroelectrochemistry.

The benign nature of defects in lead halide perovskites is widely regarded as the basis for their outstanding optoelectronic properties. Here Righetto et al. overthrew this perception, revealing the defects’ surprising potency to hot carriers and devised a strategy to suppress them.

Introducing plasma seeds, 3D ultrafast laser writing inside silicon reaches a new performance level. The researchers showcase a method that enables precise and reversible modifications, opening the door to monolithic memory technologies and reconfigurable optical devices.

The hot carriers in halide perovskite nanocrystals cool much slower than those in conventional semiconductor nanocrystals due to the phonon bottleneck. Here, Li et al. demonstrate enhanced multiple exciton generation with lower threshold in intermediate-confined perovskite nanocrystals based on this effect.

Sustainable synthesis of valuable organic compounds like lactams relies on efficient catalysts. Here, the authors report a bimetallic silver–rhenium catalyst that selectively converts cyclic imides to lactams with high efficiency, with close silver–rhenium contact being key to its performance.

The control of magnetization by an electric field can offer new magnetic data devices. Here, controlling magnetic phases in FeRh, the authors achieve a large electroresistance response in FeRh/PMN-PT heterostructures by applying an electric field, which could be used for non-volatile memory applications.

The photoluminescence spectrum of WS₂ is modified under strain applied by an atomic force microscope probe. The free carrier redistribution yields conversion of excitons to trions with conversion efficiency approaching 100%.

Solution-processed infrared lasers that operate at room temperature are a challenge, but now researchers have achieved such a device using colloidal quantum dots.

Anti-Stokes luminescence - the emission of photons with higher energy than those absorbed – in nanomaterials is widely used for optoelectronic applications. Here the authors observe it in degenerately doped bulk InP and GaAs, indicating it as a more general property of direct bandgap semiconductors.