Terahertz-driven parametric excitation of Raman-active phonons in LaAlO$_{3}$

TL;DR

This paper demonstrates a novel method of exciting Raman-active phonons in LaAlO$_{3}$ using intense terahertz pulses, revealing subharmonic components and a parametric coupling mechanism supported by theoretical analysis.

Contribution

It introduces a new approach for parametric excitation of phonons with terahertz fields, advancing control over collective excitations in materials.

Findings

Observation of subharmonic components in phonon excitation

Successful theoretical modeling of the parametric coupling mechanism

Demonstration of terahertz-induced phonon dynamics in LaAlO$_{3}$

Abstract

Achieving parametric excitation in an oscillating physical system involves periodically adjusting one of its parameters to modulate the oscillator's natural frequency. This phenomenon has been observed in numerous systems within physics and engineering, profoundly transforming modern science and technology. Despite rapid progress, the parametric control of collective excitations, such as phonons, remains a challenge while promising to generate novel and intriguing effects in a largely unexplored field. Here, we investigate the terahertz (THz) field-induced dynamics of Raman-active phonons in the perovskite structure of LaAlO$_3$ (LAO). Utilizing intense THz pulses, we demonstrate a novel mechanism of parametric phonon excitation marked by substantial subharmonic components. Theoretical analysis can successfully capture the hallmarks of the observed phenomena in a physical scenario with the THz field inducing a parametric coupling between the Raman mode and pairs of acoustic phonon excitations.