Mason Overby

Charge order in photosensitive Bi0.4Ca0.6MnO3 films

We report the structural and electronic characterization of the charge order phase in Bi0.4Ca0.6MnO3 films, in which photoinduced resistivity changes have been observed at temperatures approaching room temperature. Lattice distortions associated with the charge order are observed in all films, and both the wavevectors and displacements of the distortions are in the plane of the film. Films under compressive and tensile strain are observed to have different resonant x-ray scattering characteristics—a result that may shed light on the mechanism responsible for the photosensitivity exhibited by this material.

Nonbolometric photoresponse in (La,Pr)0.67Ca0.33MnO3 thin films

We have studied light-induced resistance changes (photoresponse) in the colossal magnetoresistive manganite material (La,Pr)0.67Ca0.33MnO3. The metal-insulator transition in this material is understood to be driven by the percolation of the metallic channel in an inhomogeneous matrix of insulating and metallic components. Our experiments reveal a nonthermal (nonbolometric) component of the light-induced resistance change, in addition to the expected resistance change related to heating (bolometric effect). This nonthermal component is seen only in the metal-insulator transition region. Our results suggest that this component may be associated with the light-induced resistance decrease in the insulating regions through an electronic mechanism.