所庆50周年系列学术活动之学术报告--Picoseconds Observation of Polarization Clusters in BaTiO3 by X-ray Laser Speckle Technique
报告题目：Picoseconds Observation of Polarization Clusters in BaTiO3 by X-ray Laser Speckle Technique报 告 人：Prof. Kazumichi Namikawa (並河一道)
Department of Physics, Tokyo Gakugei University, JAPAN
报告时间：12月17日上午9：00-10：00
报告地点：所张江园区大报告厅
摘要：Polarization domain has long been recognized and interested from early days of ferroelectrics research from application and fundamental point of view. Mean while the behavior of the response of nanostructure among the polarization domain at near the phase transition temperature under an external electric field is the vital for the understanding of the high performance of the ferroelectrics. X-ray photon correlation spectroscopy (XPCS) by means of synchrotron radiation (SR) is applied to observe relaxation phenomena of the nanostructure in matters. However, due to the low coherent flux of SR, 0.1% order of total flux, it is difficult to apply the SR XPCS to the fast phenomena with relaxation time faster than 100?sec or so. On the other hands, plasma based soft X-ray laser (SXRL) however contains within its one pulse as many photons as SR X-ray accumulated for one second. Using the X-ray laser, we can perform XPCS experiments in the picoseconds region applying, for example, to the fast relaxation phenomenon in phase transition of ferroelectric material BaTiO3. Here we show our series of experiments by X-ray laser speckle technique on polarization clusters in BaTiO3 which appears as a precursor phenomenon of phase transition.
As the first application of the X-ray laser speckle technique, structure change in domain texture has been observed in temperature dependence of the speckle pattern in BaTiO3 ferroelectric phase. As the second application, existence of the polarization clusters near Tc in parraelectric phase has been confirmed by use of the snap shot X-ray laser speckle technique from both temperature and electric field dependences of the speckle pattern. Cluster size, cluster distance, and polarization of the clusters are evaluated from a spatial correlation functions obtained from the distribution of the speckle intensity. As the third application, constructing with a time correlation measurement system equipped with a Michelson type delay generator applicable to the single shot X-ray laser, an intensity correlation of speckle from BaTiO3 has been measured above near the Tc. Fitting the time correlation function of the intensity by the exponential decay curve, we determined the characteristic relaxation time of the cluster polarization. Temperature dependence of both relaxation time and polarization take maximum at near the temperature 5 K above the Tc. This fact means a kind of critical slowing down take place within the polarization clusters at this temperature.
报告题目：Recent topics in soft x-ray solid state spectroscopy and photo-induced structural phase transitions
报 告 人：Prof. Keiichiro Nasu (那须奎一郎)，
Solid State Theory Division, Institute of Material Structure Science, High Energy Accelerator Research Organization (KEK),
Graduate University for Advanced Studies,
Japan Science and Technology Agency ( JST), CREST,
JAPAN
报告时间：12月17日上午10：00-11：00
报告地点：所张江园区大报告厅
摘要：Recent topics in the soft x-ray solid state spectroscopy and the photo-induced structural phase transitions are reviewed.
1) At first, using a new path-integral theory, we study competitions between coherence and incoherence appeared in the momentum specified photoemission spectra (MSPES) of one- two- and three-dimensional metallic many-electron systems.
2) In the second, we review the theory for creation and annihilation dynamics of a ferro-electric nano-domain, by the use of soft x-ray laser, in the BaBiO3 just above Tc. The quantum Monte Carlo method is firstly applied to this real (, not usual imaginary ) time nonlinear dynamics.
3) Finally, the graphite-diamond structural phase conversion is shown to occur only by the irradiation of a few visible lights, with neither extreme high pressure nor high temperature, and a new intermediate phase called “diaphite” is introduced.
欢迎大家参加！
相关附件