Millimeter wave sensing of materials part 2: on tip

The millimeter-wave regime has long been regarded as a frequency gap between conventional microwave and terahertz techniques. We report the development of a millimeter-wave impedance microscopy (MMIM) platform with W-band frequency tunability, uniquely combining spectroscopy and microscopy with sub-100 nm spatial resolution. Finite-element simulations reveal the near-field electric-field distribution and enable quantitative extraction of local conductivity and permittivity. The instrument achieves ultrahigh readout sensitivity and versatile functionality across a large frequency range. We further discuss efforts to extend MMIM toward quantum sensing, enabling nanoscale exploration of correlated electrodynamic responses and emergent anyonic phenomena.