Atomic-scale dynamics of strongly correlated materials: driving and seeing coherence with light at THz to x-ray frequencies*

The broad range of strongly correlated and "quantum" materials often exhibit surprisingly strong interactions between electronic, magnetic and structural properties that can manifest as strong and complex responses to impulsive excitations. Recent advances in ultrafast technology spanning freuqencies from THz to x-rays have enabled a new generation of experiments, where light can be tuned to selectively excite and probe different aspects of sprtingly correlated materials, giving a more complete and understandable picture of the interactions in both near-equilibrium and in a strongly driven regime. Here I give an overview of some of our recent work covering two directions of development in this area. The first direction is using low-frequency (THz) pulses to drive coherent vibrational dynamics in correlated systems with minimal electronic excitation. I will discuss recent examples of this in wide gap insulators and in low conductivity metals. The second direction, complementary to the first, is to use femtosecond hard x-ray scattering techniques to quantitatively measure coherent lattice dynamcis in response to impulsive excitaiton. One recent example that will be discussed is the recent observation of and ultrafast manifestation of the Einstein-de Haas effect in a ferromagentic system [1]. I will also discuss THz-driven dynamics in ferroelectric systems that represent the confluence of these two directions and shows the potential of these new methods.

[1] C. Dornes et al. "The Ultrafast Einstein de Haas Effect." Nature 565, 209-212 (2019)