Dresden 2009 – scientific programme

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MA: Fachverband Magnetismus

MA 32: Magnetic Thin Films III

MA 32.6: Talk

Thursday, March 26, 2009, 11:30–11:45, HSZ 403

Large photoconductivity and light-induced recovery of the insulator-metal transition in La_0.7Ce_0.3MnO_3−δ thin films — •Andreas Thiessen¹, Elke Beyreuther¹, Stefan Grafström¹, Kathrin Dörr², and Lukas M. Eng¹ — ¹Institut für Angewandte Photophysik, Technische Universität Dresden, D-01062 Dresden, Germany — ²Institut für Metallische Werkstoffe, IFW Dresden, D-01171Dresden, Germany

Tetravalent-ion-doped lanthanum manganite films typically suffer from overoxygenation in the as-prepared state, which in turn leads to an effective hole doping instead of the nominal and desired electron doping. This problem can be overcome by post-deposition annealing in a reducing atmosphere, which, however, removes the typical phase transition from a paramagnetic insulating to a ferromagnetic metallic phase and makes the films insulating in the whole temperature range.

Such electron-doped La_0.7Ce_0.3MnO_3−δ thin films were investigated with respect to their transport characteristics under photoexcitation. While the films are insulating in the dark, even exposure to diffuse daylight dramatically decreases the low-temperature resistance and recovers the insulator-metal transition (IMT). Exposure to continuous visible laser light further decreases the resistance by up to seven orders of magnitude and shifts the IMT towards higher temperatures. Investigations of the spectral, transient, and intensity-dependent behaviour of the photoconductivity suggest that (i) both photogeneration of carriers in the film as well as charge injection from the substrate contribute to the effect, and that (ii) the excess carriers are electrons.