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Abstract:
We report temperature-and magnetic-field-dependent measurements of the dc resistivity and the far-infrared reflectivity (FIR) (photon energies (h) over bar omega = 50-700 cm(-1)) of superlattices comprising ten consecutive unit cells of the antiferromagnetic insulator CaMnO(3), and four to ten unit cells of the correlated paramagnetic metal CaRuO(3). Below the Neel temperature of CaMnO(3), the dc resistivity exhibits a logarithmic divergence upon cooling, which is associated with a large negative, isotropic magnetoresistance. The omega -> 0 extrapolation of the resistivity extracted from the FIR reflectivity, on the other hand, shows a much weaker temperature and field dependence. We attribute this behavior to scattering of itinerant charge carriers in CaRuO(3) from sparse, spatially isolated magnetic defects at the CaMnO(3)-CaRuO(3) interfaces. This field-tunable "transport bottleneck" effect may prove useful for functional metal-oxide devices.
