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

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.Comment: 9 pages, 8 figure

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

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.Comment: 9 pages, 3 figure

Observation of 90° domain walls in relaxor ferroelectrics PMN-28.6%PT by focusing upon the CTR scattering

Rod-shaped scattering has been observed in the tetragonal phase of Pb(Mg1/3Nb2/3)O3-28.7%PbTiO3 by use of the backscattering setting. We attribute it to crystal truncation rod (CTR) scattering associated with the boundary of 90$^\circ$ domains. The CTR scattering shows a characteristic temperature evolution, which enables us to discuss the properties of the domain walls, especially their temperature dependence on the domain wall widths. Though it is necessary to have a situation where the crystal coherence is suddenly truncated, like the 90 deg. domain wall, CTR scattering can be expected to be a powerful tool for examining the domain wall properties

Mesoscopic hierarchic polarization structure in relaxor ferroelectrics Pb[(Mg1/3Nb2/3)1-xTix]O3

Mesoscopic polarization structures such as polar nanoregions and polarization domain walls are the key factors that connecting microscopic fundamental polarization structures with macroscopic practical dielectric properties. Snapshot observation of domain in the relaxor-ferroelectrics PMN-x%PT just vicinity of morphotropic phase boundary region was performed by use of 7 ps single shot soft X-ray laser pulse. A self-assembled evolution of oblique polarization domain was observed in PMN-27.8%PT under the sample temperature decreased with thermal equilibrium condition. Based on energetic discussion, anti-phase shift of domain wall pairs keeping with flat boundaries was proposed for the dielectric response. A sharp enhancement in dielectric response at the vicinity of morphotropic phase boundary region reported previously was recognized as an evidence for hierarchic nature of the present oblique polarization domain wall