1. Condensed-Matter Physics & Materials Science Seminar

    "Application of Ultrafast Electron Diffraction to Study Phase Transition in LaxSr1-xMnO3"

    Presented by Junjie Li, University of Illinois

    Monday, June 3, 2013, 11 am
    Bldg. 480 conference room

    Hosted by: Yimei Zhu

    Extensive theoretical and experimental studies show that charge, spin and lattice in CMR materials are strongly coupled one another and the interplay among these degrees of freedoms creates a complex phase diagram with multiple competing phases. However, there has been very few report on the direct observation of photoinduced structure phase transition, especially the ones related to local Jahn-Teller lattice distortion, in colossal magnetoresistive materials. The first part of this talk will present a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 using ultrafast electron diffraction (UED). The melting of orthorhombic lattice ordering under femtosecond optical excitation will be shown to involve two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent much slower transformation in 50 ps and longer timescales. The second part of talk will show recent work to solve two problems crucial to UED measurement in strongly correlated system. One is to attenuate Transient Electric field accompanying other targeted laser-triggered processes, and the other is to fabricate an electron-transparent single crystal sample in a large area, which is crucial in UED measurement due to its large electron beam size.