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Despite exhibiting ferroelectric features, SrTiO₃ fails to display long-range polar order at low temperatures due to quantum fluctuations. An ultrafast X-ray diffraction experiment now probes polar dynamics of this material at the nanometre scale.

A low-loss cavity is shown to store X-ray laser pulses for >2.8 μs.

Nanoscale dimensions can lead to unique functional properties, often achieved via large-amplitude strains. Here, the authors use femtosecond X-rays to visualize light-induced strains in semiconductor nanocrystals, showing that they correspond to anisotropic ‘breathing modes’, which collapse after straining.

Localized chemical events such as the breakage of a bond between a protein and a ligand may trigger a global protein conformational change. Here, the authors use an X-ray free-electron laser to track the motion of myoglobin in response to photoinduced ligand release, and observe a picosecond proteinquake.

A transition from ballistic to diffusive motion within 10 ps is observed in supercritical carbon dioxide with X-ray photon correlation spectroscopy. Collisions of unbound molecules with clusters are responsible for the ultrafast momentum exchange.

The interplay between charge density wave states in emerging kagome superconductors is a topic of ongoing debate. Here, the authors unveil the out-of-equilibrium competition between two coexisting charge density waves in CsV₃Sb₅ by harnessing time-resolved X-ray diffraction.

Understanding transformations of non-equilibrium materials is a key open scientific question. Here the pathway by which different polar supertextures undergo dynamical correlations and collectively transform into a metastable supercrystal state is revealed experimentally and theoretically over seven orders of magnitude timescale.

A dynamical study shows that vortices of electrical polarization have higher frequencies and smaller size than their magnetic counterparts, properties that are promising for electric-field-driven data processing.

Pump-probe spectroscopy is routinely used to interrogate ultrafast valence electronic and vibrational dynamics in complex systems. Here, the authors extend this technique to the X-ray regime using a sequence of femtosecond X-ray pulses to understand core-valence interactions in a solvated molecular complex.

Laser ablation is a phenomenon where the fundamental research directly intersects with practical relevance for industrial applications, yet probing the highly nonequilibrium phase decomposition triggered by laser excitation is still a challenge. This study provides unique insights into the dynamics of nanoscale phase decomposition in laser ablation of thin gold films by combining time-resolved femtosecond X-ray probing with large-scale atomistic modeling.

Ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remain challenging to describe since electronic/nuclear configurations are coupled. Here the authors use time-resolved X-ray absorption spectroscopy to probe the light-induced spin-state trapping dynamics of [Fe(bpy)₃]²⁺beyond the Born-Oppenheimer approximation.

Interactions between reactive excited states of molecular photocatalysts and surrounding solvent can dictate reaction pathways, but are not readily accessible to conventional spectroscopic methods. Here the authors use diffuse X-ray scattering and theory to study the atomistic solvation dynamics of a photoexcited di-iridium complex in acetonitrile.

Electron–phonon coupling in a monolayer WSe₂ on a substrate is investigated by femtosecond surface X-ray scattering. Counterintuitively, the absorbed optical photon energy is dominantly coupled to the in-plane lattice vibrations within 1 ps.

Free electron X-ray laser pulses, generated by self-amplified spontaneous emission, are stochastic in nature. Here the authors present a reconstruction method for 2D spectroscopy while preserving the intrinsic properties of the incident pulses and apply it to a study towards X-ray intensity induced effects.

A robust acoustic droplet ejection–drop-on-tape method delivers samples to an X-ray free-electron laser source for combined serial femtosecond crystallography and X-ray emission spectroscopy analysis, providing detailed insights into macromolecular reaction dynamics.

Future cavity-based XFEL sources require optics stable to hundreds of nanometers and nanoradian. We present how laser interferometry metrology and feedback control achieve this even during energy and delay scans.

The dynamics of liquid water is rich due to its complex, highly disordered hydrogen-bond network, which hasn’t been fully understood. Perakis et al. measure water dynamics at sub-100 fs and show that it cannot be described by simple thermal motion due to the build-up of tetrahedral structures upon supercooling.

Diffuse X-ray scattering with femtosecond resolution shows the formation and relaxation of polaronic distortions in halide perovskites. These structural changes are also quantified and correlated to transient changes in carrier effective mass.

Femtosecond time-resolved X-ray diffraction reveals that in the ultrafast demagnitization of ferromagnetic iron, about 80% of the angular momentum lost from the spins is transferred to the lattice on a sub-picosecond timescale.

Femtosecond resolution X-ray fluorescence spectroscopy is shown to track the charge and spin dynamics triggered when an iron coordination complex is excited by light, and establishes the critical role of intermediate spin states in the de-excitation process.

The structures of three intermediate states of photosystem II, which is crucial for photosynthesis, have been solved at room temperature, shedding new light on this process.

Charge and spin density waves describe periodic distortions to the electronic structure of a given system and ultrafast laser techniques can provide unique mechanistic insight into their underling physics. Here, the authors use femtosecond laser pulses to understand the role phonon dynamics play in the formation of a spin density wave in Cr thin films.