Excitonic condensation in bulk crystals is hard to separate from charge-density-wave formation, and probes that depend on long-range order lose sensitivity above T_c. In this work we used few-femtosecond broadband extreme-ultraviolet absorption spectroscopy (UBXAS) to follow exciton dissociation in 1T-TiSe₂ as a function of pump fluence and temperature. The Se M_4,5 edge reports on the transient population of Se 4p holes through local dipole transitions, so it stays sensitive when long-range phase coherence is gone.

We found that the initial response time scales as one over square root of fluence both below and above T_c ≈ 200 K, the signature of exciton breaking by plasmon screening. Short-range excitonic correlations therefore emerge before long-range order forms in the ground state. Close to T_c the response becomes fast and independent of fluence, consistent with a diverging excitonic susceptibility. A dominant phonon contribution is ruled out, since the response time drops threefold while the CDW phonon frequency renormalizes by only 20%.

This gives a direct observable for excitonic fluctuations outside the thermodynamically ordered phase, and it transfers to other excitonic insulator candidates in quasi-one- and quasi-two-dimensional crystals.

Congratulations to Alfred, Sheng-Chih, Emma, Bailey, Marcus and the whole team, and thanks to our collaborators at Shanghai Jiao Tong University, ShanghaiTech University, Tohoku University and SSRL.

The paper is now out open access in Nature Physics at https://doi.org/10.1038/s41567-026-03423-z

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