Imaging topological matter with microwaves

In recent years, microwave impedance microscopy (MIM) has shown great promise for the investigation of topological states of matter and many-body phenomena in quantum materials and devices. In this talk, I will discuss the development of a new MIM in a dilution refrigerator, which achieves the spatially-resolved detection of electronic states at temperatures down to 50 milliKelvin. I will describe how this technique can be used to visualize chiral edge modes and topological phase transitions in two dimensions.

To offer a glimpse into the third dimension, I will introduce a new 3d imaging approach that resolves states on individual atomic planes of a van der Waals heterostructure, layer by layer. To illustrate the key ideas, I will discuss layer-resolved microwave readout of quantum Hall states and density fluctuations in double-layer graphene. By visualizing charge disorder on different planes, we shed light on the impact of surface impurities and screening on the formation of exotic fractional topological phases. At the same time, resolving how charge is distributed out-of-plane offers a quantitative probe of the local electronic compressibility and the nature of many-body correlations. This approach opens a new route for microscopy with displacement field control, which unlocks access to a wide range of exotic phenomena that can only be realized in multi-layer structures and top-gated devices.

Speaker: Monica Allen, UC San Diego