Thursday, February 2nd: Dynamics, control, and metastability in correlated oxides

Event Date: 

Thursday, February 2, 2017 - 3:30pm

Event Location: 

  • 1605 CNSI (Elings Hall)

The macroscopic response of numerous correlated transition metal oxides is strongly influenced by mesoscopic phenomena including phase coexistence. This manifests in the dynamic response of these materials that can be probed – with the looming grand challenge of control – using ultrafast optical pulses. The insulator to metal transition (IMT) is a particularly rich example, with interesting questions being experimentally addressed in materials that include manganites, vanadates, and nickelates: What are the characteristic timescales of the IMT? Can a phase transition be driven along distinct pathways, and can long-lived nonequilibrium states be accessed? I will present results of our recent investigations of IMT dynamics utilizing optical-pump terahertz-probe spectroscopy to measure conductivity changes with sub-picosecond resolution. As one example, we have investigated manganite (La0.7Ca0.3MnO3) thin films that have been strain-engineered to quench the thermal IMT. This yields, at all temperatures, a robust insulating phase resulting from strain-enhanced orthorhombic distortion of the underlying octahedral framework. Short pulse photoexcitation initiates a nonthermal IMT to a persistent “hidden” metallic phase. Our measurements reveal that the transition is cooperative and ultrafast, requiring a critical absorbed photon density to activate local charge excitations that mediate magnetic-lattice coupling stabilizing the metallic phase. I will also present near-field nanoscopy characterization results of the photo-induced metastable state.