Speaker:
Jing Tao, Brookhaven National Laboratory

Abstract:
Understanding the structural origin of materials’ functionality is often challenging to obtain via equilibrium states but promising to unveil through the observation of non-equilibrium processes. The successful development of femtosecond laser systems and pump-probe techniques in the past three decades has enabled us to probe ultrafast dynamics in a variety of materials. Particularly, taking advantages of strong interaction with matter during scattering, ultrafast electron diffraction (UED) technique provides unique opportunities to study the non-equilibrium dynamics. In this talk, we will demonstrate a few UED projects to address the intriguing coupling between electronic degrees of freedom and lattice in quantum materials. One of the projects is the exploration of structural dynamics in superionic Cu2S nanomaterials. Through a structural phase transition in Cu2S, we followed the transient states along the transition pathway and identified distinct time scales for crystal symmetry change and lattice expansion. Based on the UED observations, we argue that the mechanism of the structural phase transition in Cu2S is dominated by electron-phonon coupling [1, 2]. In addition, we will show crystal refinement work using UED results during the pump-probe processes in a 1T-TaSeTe single-crystal sample to understand charge-density-wave (CDW) formation mechanism and charge-lattice interaction in this material.

References:
[1]. J. Tao et al., “Reversible structure manipulation by tuning carrier concentration in metastable Cu2S”, PNAS 114, 9832 (2017).
[2]. J. Li et al., “Probing the pathway of an ultrafast structural phase transition to illuminate the transition mechanism in Cu2S”, Appl. Phys. Lett. 113, 041904 (2018).