Department of Physics
Condensed Matter Seminar

We have developed coaxial cantilever probes for near-field microwave (1GHz) imaging on atomic-force microscope platforms. During the xy-scan, the real and imaginary parts of the tip-sample impedance are detected by the microwave electronics. Local electrical imaging with a spatial resolution ~100nm determined by the tip diameter has been obtained on doped semiconductors, graphene in various modalities, and phase-change nanoribbon devices. The microwave impedance microscope is also implemented under variable temperatures 2-300K and high magnetic fields up to 9T. We discovered a pronounced mesoscopic percolating network in a colossal magnetoresistive manganite (Nd0.5Sr0.5MnO3) thin film. Strikingly, the filamentary metallic domains emergent from the charge/orbital-ordered insulating background align preferentially along certain crystal axes of the substrate, indicating substrate-induced strain fields as the underlying mechanism. The microwave images revealed drastically different domain structures between the zero-field-cool and field-cool processes, consistent with the macroscopic transport measurements.