Accessing the earliest electronic response of quantum materials requires combining few-femtosecond time resolution with element specificity and control over temperature. In this work, we introduce a table-top cryogenic ultrafast broadband XUV absorption spectroscopy beamline that spans 22–73 eV, reaches temperatures down to 20 K, and provides sub-50-meV energy resolution with a sub-10-fs instrument response.

Using the van der Waals multiferroic NiI₂ as a benchmark, we resolve temperature-dependent changes across its magnetic phase transitions and track the element-specific response on the femtosecond timescale. The instrument opens a route to studying the initial electronic response and emergence of nonequilibrium states in quantum materials with simultaneous ultrafast, element-specific, and cryogenic sensitivity.

The preprint can be found here: https://arxiv.org/abs/2608.03955

Most ultrafast pump-probe experiments average over many laser shots and discard the shot-to-shot variation in the sample response. In this work we kept that variation instead of averaging it away. Using time-resolved X-ray micro-diffraction at the Advanced Photon Source, we tracked the lattice response of a single grain of Li_0.5La_0.5TiO₃, a solid-state lithium ion conductor, after each pump pulse.

We found that the lattice trajectories were not independent from shot to shot. Neighboring pump-probe events showed correlated lattice expansion and relaxation, with a correlation “length” of about 1500 laser shots. That length corresponds to an energy barrier of 0.4 ± 0.1 eV, close to the known activation energy for lithium ion migration in this material. A simple Markov-chain model reproduces the effect and points to lithium hopping as the microscopic origin.

We call this approach nonequilibrium noise correlation spectroscopy. It gives a way to extract hidden dynamical correlations from data that would normally be treated as noise, with applications beyond ionic conductors to any system with stochastic photoinduced dynamics.

Congratulations to Jackson, Alfred and the team. We are especially delighted that our article was chosen as an Editors’ Highlight.

The paper is now out in Nature Communications open access: https://www.nature.com/articles/s41467-026-72663-7

Our Comment in Physical Review Letters examines a recent report of helicity-dependent charge-density-wave dynamics in 1T-TiSe₂. Using MeV ultrafast electron diffraction with a near-collinear pump-probe geometry and carefully characterized circular pump polarization, we find no measurable circular dichroism in the transient CDW response for either 800 nm or 10.6 µm excitation. Our results suggest that the previously reported effect may be complicated by grazing-incidence excitation, which substantially alters the polarization state inside the sample. This work highlights the need for careful control of optical geometry and polarization when probing chiral order in quantum materials.

Measurements were done at the MeV-UED user facility at SLAC in collaboration with the groups of Alfred Zong (Stanford) and Giulio Cerullo (Politecnico Milan).

Link to the open access publication: https://journals.aps.org/prl/abstract/10.1103/p5d8-548h