Quantum Monte Carlo study on speckle variation due to photorelaxation of ferroelectric clusters in paraelectric barium titanate

TL;DR

This study uses quantum Monte Carlo simulations to analyze how ferroelectric cluster relaxation affects speckle pattern variations in paraelectric barium titanate, revealing critical slowing down near phase transition.

Contribution

It introduces a theoretical model linking speckle pattern dynamics to ferroelectric cluster relaxation and critical phenomena in barium titanate.

Findings

Speckle variation correlates with ferroelectric cluster relaxation dynamics.

Critical slowing down occurs as temperature approaches the transition point.

Quantum Monte Carlo simulations reveal the relation between dipole fluctuations and structure.

Abstract

Time-dependent speckle pattern of paraelectric barium titanate observed in a soft x-ray laser pump-probe measurement is theoretically investigated as a correlated optical response to the pump and probe pulses. The scattering probability is calculated based on a model with coupled soft x-ray photon and ferroelectric phonon mode. It is found that the speckle variation is related with the relaxation dynamics of ferroelectric clusters created by the pump pulse. Additionally, critical slowing down of cluster relaxation arises on decreasing temperature towards the paraelectric-ferroelectric transition temperature. Relation between critical slowing down, local dipole fluctuation and crystal structure are revealed by quantum Monte Carlo simulation.