Theory of Time-Resolved Raman Scattering in Correlated Systems: Ultrafast Engineering of Spin Dynamics and Detection of Thermalization

TL;DR

This paper develops a theoretical framework for nonresonant time-resolved Raman scattering to probe and manipulate ultrafast spin dynamics in strongly correlated electron systems, supported by simulations of the Hubbard model.

Contribution

It introduces a generic theory for nonequilibrium Raman scattering and demonstrates its effectiveness in capturing ultrafast processes in correlated materials.

Findings

Floquet theory captures bimagnon softening under high-frequency pumps

Effective heating dominates at low pump fluences

Coherent many-body effects emerge at higher pump amplitudes and resonant conditions

Abstract

Ultrafast characterization and control of many-body interactions and elementary excitations are critical to understanding and manipulating emergent phenomena in strongly correlated systems. In particular, spin interaction plays an important role in unconventional superconductivity, but efficient tools for probing spin dynamics especially out of equilibrium, are still lacking. To address this question, we develop a theory for nonresonant time-resolved Raman scattering, which can be a generic and powerful tool for nonequilibrium studies. We also use exact diagonalization to simulate the pump-probe dynamics of correlated electrons in the square-lattice single-band Hubbard model. Different ultrafast processes are shown to exist in the time-resolved Raman spectra and dominate under different pump conditions. For high-frequency and off-resonance pumps, we show that the Floquet theory works well in capturing the softening of bimagnon excitation. By comparing the Stokes/anti-Stokes spectra, we also show that effective heating dominates at small pump fluences, while a coherent many-body effect starts to take over at larger pump amplitudes and frequencies on resonance to the Mott gap. Time-resolved Raman scattering thereby provides the platform to explore different ultrafast processes and design material properties out of equilibrium.