Exploring and Manipulating Materials with Ultrafast Linear and Nonlinear Scattering and Spectroscopy Techniques

PC Department Seminar
Date: Jun 21, 2024
Time: 11:00 AM (Local Time Germany)
Speaker: Michael Zuerch
University of California at Berkeley, USA
Location: Building G
Room: 2.06
Host: Martin Wolf

Our group specializes in ultrafast spectroscopic methods, enabling in-depth studies of material chemistry in intricate environments and the control of quantum phenomena on femtosecond timescales. In the first part of this seminar, I will discuss the role of lithium in various systems from its contribution to symmetry breaking (LiNbO₃), to an exotic quantum material (polar metal LiOsO₃), to unravel the reasons behind the low hopping rate of lithium ions at the surface of a solid-state electrolyte (Li_xLa_(2-x)/3TiO₃). All these systems share the common feature that Li occupies a symmetry-broken state which we can selectively probe using extreme-ultraviolet second-harmonic generation spectroscopy (XUV-SHG), a novel spectroscopy pioneered in my group. In the second part I will discuss recent results on 1T-TiSe₂, a prototypical charge-density-wave (CDW) compound that also exhibits strong excitonic correlations in its low-temperature phase.

I will discuss how we unravel the interplay of these different aspects via cryogenic attosecond transient extreme-ultraviolet absorption spectroscopy (cryo-ATAS), for which we built a unique laboratory instrument, and mega-electron-volt ultrafast electron diffraction (MeV-UED). I will show how photoexcitation leads to a 3D-to-2D dimension crossover in the CDW order parameter, a process dictated by the excitonic correlations in the system. The excitonic effect is further evidenced in the initial response of selected core-level absorption edges, and these observations help pinpoint the specific role of excitonic correlations in the CDW transition. I will also illustrate the hidden 1D nature of the CDW and its implications for the formation mechanism of domain-wall-like topological defects, which are found to emerge well under one picosecond following photoexcitation.

References:

T. Helk et al., Sci. Adv. 7, eabe2265 (2021).

C. Uzundal et al., Phys. Rev. Lett. 127, 237402 (2021).

E. Berger et al., Nano Letters 21, 6095–6101 (2021).

Y. Cheng et al., Nature Communications 13, 963 (2022)

C. Woodahl et al., Nature Materials 22, 848 (2023)

A. Zong et al., Nature Reviews Materials 8, 224–240 (2023)

Y. Cheng et al., Nature Physics 20, 54–60 (2024)

J. McClellan et al., arXiv:2406.06832 (2024)