Nonequilibrium quantum dynamics in SrTiO₃ under impulsive THz radiation with machine learning.

Area of Science:

• Condensed Matter Physics
• Quantum Dynamics
• Materials Science

Background:

• Probing transient states of matter via photoexcitation is crucial but limited by challenges in accessing microscopic behavior, especially nuclear quantum effects.
• Understanding microscopic processes in photoexcited materials, like strontium titanate (SrTiO3), is essential for materials science.
• Current models struggle to capture complex quantum dynamics in nonequilibrium regimes.

Purpose of the Study:

• To simulate and understand the quantum nuclear dynamics of SrTiO3 after terahertz laser pumping.
• To elucidate the microscopic origin of experimentally observed phonon upconversion.
• To explore the potential of terahertz pulses in inducing novel material properties like polar order.

Main Methods:

• Combining first-principles simulations with machine learning for quantum nuclear dynamics.
• Simulating nonequilibrium quantum dynamics beyond the current state of the art.
• Analyzing terahertz laser pumping effects on SrTiO3 at a microscopic level.

Main Results:

• Unveiled complex quantum dynamics of SrTiO3 following terahertz laser excitation.
• Disclosed the microscopic origin of phonon upconversion, a phenomenon not fully understood.
• Quantified the lifetime of out-of-equilibrium motion, surpassing simplified model capabilities.
• Predicted that terahertz pump pulses can induce persistent out-of-equilibrium stress, leading to polar order.

Conclusions:

• Advanced simulation techniques provide unprecedented insight into photoexcited quantum materials.
• Terahertz laser pumping offers a novel pathway to control and induce properties like polar order in materials.
• This work establishes a foundation for exploring photoexcitation effects in complex quantum materials.