QMC Colloquium: Mariano Trigo - Stanford

Transient textured phases uncovered by ultrafast x-ray scattering




Ultrafast optical excitation can drive materials into novel states that cannot be accesed in
equilibrium. Visualizing the pathways of transformation into those states can inspire rational
ways to control materials’ functionality. In this talk will show two examples where
femtosecond x-ray scattering at free-electron lasers (XFELs) uncovers hidden and transient
orders.

First, strong terahertz (THz) pulses induce transient ferroelectricity in the quantum
paraelectric SrTiO3, yet equilibrium studies hint at a hidden phase with spatially modulated
polarization. Our results on THz-driven diffuse X-ray scattering uncovers hybrid polaracoustic
modes that soften at wavelengths of tens of nanometers, precursors of an incipient
phase with spatially modulated polarization [1]. Furthermore, under only moderate uniaxial
strain a new amplitude mode emerges at finite wavevector while the crystal remains
inversion-symmetric on long length scales, the signature of a strain-stabilized phase with
nanoscale polar texture. This hints at unstrained SrTiO3 being the disordered side of this
transition rather than a conventional incipient ferroelectric.

Second, fast non-adiabatic passage through a phase transition generates topological
defects that govern the return to equilibrium, as well as phase competition, yet their
dynamics have remained elusive. After strong photoexcitation of the incommensurate
charge density waves (CDW) in SmTe3 and LaTe3, we directly observe the creation and
evolution of such defects [2]. Scaling and self-similarity of the intensity identifies them as
vortex strings, i.e. dislocations of the CDW. I will discuss the impact of these defects in the
long-term stability of a competing CDW order recently observed in LaTe3.
Together, these results highlight momentum-resolved ultrafast probes as an incisive tool for
uncovering hidden transient orders in quantum materials.


References
[1] G. Orenstein et al., Nat. Phys. 21, 961 (2025).
[2] G. Orenstein et al., Phys. Rev. X 15, 031058 (2025).





Host: Sternbach