Toward nonthermal control of excited quantum materials: framework and investigations by ultrafast electron scattering and imaging

TL;DR

This paper develops a theoretical framework and experimental investigations using ultrafast electron scattering to understand nonthermal phase transitions and long-range dynamics in excited quantum materials induced by ultrashort laser pulses.

Contribution

It introduces a comprehensive approach combining ultrafast electron scattering, imaging, and modeling to study non-equilibrium phases and dynamics in quantum materials.

Findings

Identification of nonthermal critical points in quantum materials.

Observation of hidden phases induced by light excitation.

Insights into non-equilibrium relaxation processes in various materials.

Abstract

Quantum material systems upon applying ultrashort laser pulses provide a rich platform to access excited material phases and their transformations that are not entirely like their equilibrium counterparts. The addressability and potential controls of metastable or long-trapped out-of-equilibrium phases have motivated interests both for the purposes of understanding the nonequilibrium physics and advancing the quantum technologies. Thus far, the dynamical spectroscopic probes eminently focus on microscopic electronic and phonon responses. For characterizing the long-range dynamics, such as order parameter fields and fluctuation effects, the ultrafast scattering probes offer direct sensitivity. Bridging the connections between the microscopic dynamics and macroscopic responses is central toward establishing the nonequilibrium physics behind the light-induced phases. Here, we present a path toward such understanding by cross-examining the structure factors associated with different dynamical states obtained from ultrafast electrons scattering, imaging, and modeling. We give the basic theoretical framework on describing the non-equilibrium scattering problems and briefly describe how such framework relates to the out-of-equilibrium phenomena. We give effective models outlining the emergences of nonthermal critical points, hidden phases, and non-equilibrium relaxational responses from vacuum-suspended rare-earth tritellurides, tantalum disulfides thin films, and vanadium dioxide nanocrystalline materials upon light excitations.