Dynamics of ferroelectric nano cluster in BaTiO3 observed as a real time correlation between two soft X-ray laser pulses

TL;DR

This study investigates the real-time dynamics of photo-created ferroelectric nano-clusters in BaTiO3 using soft X-ray laser pulses, revealing how cluster relaxation times vary with temperature near the phase transition.

Contribution

It introduces a theoretical model combining photon and phonon modes to simulate speckle pattern correlations and cluster relaxation dynamics in ferroelectric materials.

Findings

Cluster excitation is stable near the transition point with long relaxation times.

High temperature induces thermal fluctuations, shortening relaxation times.

Phonon spectral functions reproduce cluster softening and central peak effects.

Abstract

We carry out a theoretical investigation to clarify the dynamic property of photo-created nano-sized ferroelectric cluster observed in the paraelectric BaTiO3 as a real time correlation of speckle pattern between two soft X-ray laser pulses, at just above the paraelectric-ferroelectric phase transition temperature. Based on a model with coupled soft X-ray photon and ferroelectric phonon mode, we study the time dependence of scattering probability by using a perturbative expansion approach. The cluster-associated phonon softening as well as central peak effects are well reproduced in the phonon spectral function via quantum Monte Carlo simulation. Besides, it is found that the time dependence of speckle correlation is determined by the relaxation dynamics of ferroelectric clusters. Near the transition point, cluster excitation is stable, leading to a long relaxation time. While, at high temperature, cluster structure is subject to the thermal fluctuation, ending up with a short relaxation time.