Prof. Dr. Michael Zuerch
University of California at Berkeley und Lawrence Berkeley National Laboratory
Exploring and Manipulating Materials with Ultrafast Linear and Nonlinear Scattering and Spectroscopy Techniques
Our group develops ultrafast spectroscopic methods that use core-level and nonlinear light–matter interactions to resolve material chemistry in complex environments and to follow quantum phenomena on femtosecond timescales. In the first part of this seminar, I will discuss how lithium can act as a local symmetry-breaking coordinate across seemingly disparate materials: the ferroelectric insulator LiNbO?, the polar metal LiOsO?, and the solid-state electrolyte Li?La(???)/?TiO?. In each case, lithium occupies a locally symmetry-broken environment that can be selectively accessed with extreme-ultraviolet second-harmonic generation spectroscopy (XUV-SHG), a nonlinear X-ray spectroscopy pioneered by our group that combines symmetry sensitivity with elemental specificity [1–4]. These examples illustrate how core-level nonlinear optics can connect local structure, interfacial ion dynamics, and emergent macroscopic functionality.
In the second part, I will turn to 1T-TiSe?, a prototypical charge-density-wave compound in which lattice distortion, dimensionality, and excitonic correlations remain deeply intertwined.
Using cryogenic attosecond transient extreme-ultraviolet absorption spectroscopy (cryo-ATAS) and mega-electron-volt ultrafast electron diffraction (MeV-UED), we resolve how photoexcitation drives a 3D-to-2D crossover of the CDW order parameter, dictated by the breaking of excitonic correlations [5]. Core-level absorption further reveals signatures of long-range CDW order and short-range excitonic correlations that are difficult to isolate in equilibrium spectroscopies [6]. Finally, I will discuss the hidden one-dimensional character of the CDW and its role in the ultrafast formation of domain-wall-like topological defects, which emerge well within one picosecond after photoexcitation [7]. Together, these studies show how ultrafast XUV and electron-scattering probes can disentangle local chemistry, symmetry breaking, and many-body correlations in quantum materials.
[1] T. Helk, E. Berger, C. B. Uzundal, C. Spezzani, C. Weninger, M.
Zuerch, “Table-top extreme ultraviolet second harmonic generation,” Science Advances 7, eabe2265 (2021).
[2] C. B. Uzundal, E. Berger, T. Helk, C. Spezzani, C. Weninger, M.
Zuerch, “Polarization-resolved extreme-ultraviolet second harmonic generation from LiNbO?,” Physical Review Letters 127, 237402 (2021).
[3] E. Berger, C. B. Uzundal, T. Helk, C. Spezzani, C. Weninger, M.
Zuerch, “Extreme ultraviolet second harmonic generation spectroscopy in a polar metal,” Nano Letters 21, 6095–6101 (2021).
[4] C. Woodahl et al., “Probing lithium mobility at a solid electrolyte surface,” Nature Materials 22, 848–852 (2023).
[5] Y. Cheng et al., “Light-induced dimension crossover dictated by excitonic correlations,” Nature Communications 13, 963 (2022).
[6] A. Zong et al., “Core-level signature of long-range charge-density-wave order and short-range excitonic correlations probed by attosecond broadband spectroscopy,” arXiv:2407.00772 (2024), in press Nature Physics (2026) [7] Y. Cheng et al., “Ultrafast formation of topological defects in a two-dimensional charge density wave,” Nature Physics 20, 54–60 (2024).