This project will investigate structural phase transition dynamics in solids and the dynamical Jahn-Teller distortion in manganites. The dynamical processes will be initiated by impulsive excitation energy from a femtosecond pulse laser. Their temporal evolutions will then be probed via the newly developed technique of femtosecond electron diffraction, which directly monitors atomic motions on the timescale of a single atomic vibrational period. These measurements are accompanied by complementary femtosecond time-resolved optical spectra that are also sensitive to the relevant degrees of freedom. The aim is to gain a microscopic understanding of these dynamic processes beyond the current time-averaged thermodynamic point of view; for example, the interplay of local structural deformations on the global properties in transition-metal oxides. Issues and questions to be addressed include: (1) How the melting and recrystallization in order-disorder structural transformations in solids evolve with time, microscopically on the atomic scale; (2) How atoms rearrange themselves and evolve, time scales and possible pathways, from one distinct structure to another in solid-solid structural transformations; and (3) The role of the dynamical Jahn-Teller distortion in the colossal magnetoresistance effect, in particular, the correlations between the dynamical Jahn-Teller distortion and the other physical properties in manganites, such as the charge/orbital ordering and conductivity. Graduate students involved in the project acquire training and knowledge in one the forefront areas of contemporary condensed matter physics in preparation for advanced studies or employment in academe, industry or government.
This project is directed at the study of physical processes involving ultrafast structural changes in solid materials, in particular, laser-induced structural phase transition and the role of dynamical Jahn-Teller distortion in colossal magnetoresistance materials. A thorough understanding of these dynamic behaviors will have important scientific implications in laser-related materials processing and manufacturing, and in developing new materials in the magnetic data recording and storage industry. Graduate students involved in the project acquire training and knowledge in one the forefront areas of contemporary condensed matter physics in preparation for advanced studies or employment in academe, industry or government.
