Infrared study of a La0.7Sr0.3MnO3-δ micrometric transistor channel

We studied the polaron conductivity in a field-effect transistor (FET) based on the doped oxide La0.7Sr0.3MnO3-δ, where the electric field penetration depth is enhanced due to suppression of metallic conduction by large oxygen deficiency δ, by mid-infrared microspectroscopy (wavelengths from 1.4 to 12μm) on a 3μm wide active channel. Synchrotron radiation was used to obtain the mid-infrared response at the diffraction limit. We found that bound polarons, although clearly detected, play a minor role in the electric field-induced dc conductivity modulation, which may be then attributed to the accumulation/depletion of free carriers.