Femtosecond Studies of Coupled Electron-Lattice Dynamics in Doped Perovskite Manganites

College Of William And Mary, Williamsburg VA

Investigators

Abstract

This condensed matter physics project seeks to elucidate electron-lattice coupling, soft mode dynamics, and spin-flip processes near the metal-insulator phase transition in doped perovskite manganites. Femtosecond time-resolved optical response techniques will be employed to measure the dynamics of the various processes that dictate the unusual transport properties of the manganese oxides. The primary objective is to study the coupled dynamics of the charge carriers and that of the lattice deformations, which surround them. The advantages of the time-domain approach to investigate these heavily damped responses are clear, especially near structural phase changes where the soft modes are characteristically heavily damped or over damped. Magneto-elastic coupling is important to understand the low-temperature spin dynamics of manganite. Information about the spin dynamics will be used to test various theoretical approaches that sensitive to this parameter. A femtosecond-tunable laser system will be employed for impulsive-stimulated Raman scattering (ISRS), pump-probe transient reflectivity and magneto-optical Kerr-effect experiments. Systematic studies of the natural frequency and damping of the soft optical phonon modes by ISRS measurements will provide new information about electronic and structural instabilities and phase changes of these strongly correlated electron systems. The goal of our magnetic field-dependent studies is to elucidate correlation effects of the mobile charge carriers and their dependence on the magnetic structure of the doped manganese oxides. The students involved in this project will be trained in an interdisciplinary field including modern optics, material science, and computational modeling. Interest in the manganese oxides as exceptional candidates for magnetic sensors and detectors has been rekindled because of the colossal magnetoresistance effect observed in these materials at room temperature. Thin films open up new possibilities for applications in diverse areas of technology such as magnetic random access memories and read heads for hard disk drives. The goal of this research program is to elucidate the unusual magneto-transport properties of doped manganese oxides by studying the coupled dynamics of the charge carriers and that of the lattice deformations that surround them. Femtosecond time-resolved optical response techniques will be employed to measure the dynamics of the various processes that dictate the unusual transport properties of the manganese oxides. The goal of the magnetic field-dependent studies is to reveal correlation effects of the mobile charge carriers and their dependence on the magnetic structure of the doped manganese oxides. Experimental studies of the spin dynamics can be used to test various theoretical approaches that are sensitive to this parameter. These fundamental studies will provide new information about the mechanism that governs the large spin-dependent transport in this strongly correlated material system. The training that graduate and undergraduate students will receive while working on this project will prepare them for attractive material science or optics related careers in industry, academe, or government.