[PAST EVENT] Peng Xu: Physics Dissertation Defense
Abstract: Charge transport properties of manganites can be significantly modified by temperature, chemical doping, strain, and interfacial boundaries. In this dissertation, we report studies on broadband far-field infrared spectroscopy and near-field infrared nano-imaging of single crystalline thin films of Sr doped manganite LaMnO3 at 0.33 doping level. At this Sr-doping level, the manganite films undergo a phase transition between a ferromagnetic metallic phase at low temperatures to a paramagnetic, insulating phase at higher temperatures. We investigate an 85 nm thick La0.67Sr0.33MnO3 (LSMO) film grown on (100) lanthanum aluminate substrate, and report novel aspects of charge and lattice dynamics. We performed detailed scattering-type scanning near-field mid-infrared microscopy on an 18 nm thick LSMO film grown on (100) strontium titanate substrate. The temperature dependence of the infrared near-field data is consistent with a continuous, uniform second order phase transition. We discover critical fluctuations in the bulk of the film which we distinguish from a persistent phase coexistence regime at the film-substrate interface.
Bio: Peng Xu was born in Xi?an, China. He received his Bachelor of Science from Harbin Institute of Technology in 2008 and his Master of Science from William & Mary in 2010.