Transmission-mode microwave impedance microscopy using a photonic crystal cavity at sub-THz frequencies

In quantum materials research, reflection-mode microwave impedance microscopy (R-MIM) is instrumental in measuring local complex permittivity, especially under high magnetic fields and low temperatures. Traditionally, R-MIM has operated around 1-10 GHz. Transitioning to higher frequencies enhances sensitivity and uncovers additional condensed matter phenomena. In this work, we present two ideas: (1) the introduction of transmission-based microwave impedance microscopy (T-MIM), where the tip's near-field signal interacts with a sample and is picked up by a high-Q resonator, and (2) increasing the maximum MIM frequency from 20 GHz to 95 GHz via a silicon photonic crystal cavity. As a proof-of-principle, we fabricate and characterize a 95 GHz cavity at 298 K and 4 K.