Understanding and controlling local conductivity have been a corner stone for important scientific breakthroughs and technological inventions, as exemplified by transistor, integrated circuit, Anderson localization, quantum hall effect and fractional quantum hall effect. In these cases, local visualization and control of doping, mobility, gating, dielectric, heterostructure, and inter-diffusion are important. Microwave Impedance microscope provides a new platform to measure local electrical properties.
Microwave has several inherent advantages. It is coherent so both amplitude and phase information can be analyzed to gain quantitative insight. Its high frequency naturally leads to efficient capacitive coupling, thus no contact is needed for electrical measurement. It has much higher inherent contrast for electrical properties than optical microscopy, for conductivity diverges for metal but approaches zero for insulator. However, it also has two disadvantages – relatively poor spatial resolution and stray field coupling that compromises quantitative analysis.
In this talk, we will report our progress in developing a scalable (batch processed and shielded tip) non-resonance microwave impedance microscope that achieves a resolution ~ 30-50 nm, approaching the interesting physics length scales: localization and coherence length, the edge state width of topologically ordered systems, etc.. The non-resonance approach and merge with the AFM platform also greatly reduce many of the “practical problems” that severely compromises advances of the earlier resonator based scanning microwave microscope, such as thermal drift, height control, and tip consistency – all critical for quantitative and repeatable measurements.
The highlight of this talk will be the physics insight we gain by applying this technique to investigate topological structures of novel quantum systems, including edge state of topological order in quantum hall states of semiconductors and graphene, as well as a rich hierarchy of domain wall physics in charge ordered oxides.