Haidan Wen

Spatio-temporal imaging of nonequilibrium heterogeneities in correlated materials
Presenter Haidan Wen, Argonne National Laboratory
Session Title Probing Structure and Dynamics of Quantum Materials via X-ray Scattering at LCLS
Abstract

The competition of multiple degrees of freedom leads to dynamical processes of heterogeneities at length scales from nm to µm and at a time scale from ps to µs. The intrinsic dynamics of heterogeneity is intimately tied to a number of fundamental phenomena such as metal-to-insulator phase transitions and high temperature superconductivity . Understanding of heterogeneities in this cross-over regime of time and space is essential for developing, controlling, and applying these emergent properties to next-generation technologies.

In this talk, I will present the recent efforts at the Advanced Photon Source to visualize the dynamics of mesoscale heterogeneities, opening a new avenue to understanding complex interaction of correlated materials. The first example is a study of structural phase progression in VO2 by time-resolved hard x-ray microscopy. Following a homogenous in-plane optical excitation, the macroscopic phase transformation is initiated at discrete pinning sites and completed by the growth of one lattice structure into the other as a result of a displacive lattice transformation in superheated VO2, rather than driven by thermal transport. The second example is a study of strong THz field driving structural dynamics of ferroelectrics, where the THz field is resonantly excite the lattice mode that results in an effective ionic motion.

In combination of near-field THz enhancement and the time-resolved x-ray diffraction microscopy, we revealed the local strain profile as a result of THz excitation. These results highlight the need for future material characterization, an ultrafast multimodal imaging platform utilizing radiation at x-ray, optical and THz frequencies.