Microwave investigation of highly-ordered electronic phases in graphene

The fragile nature of quantum phases makes them difficult to realize and probe experimentally. One of the prerequisites for studying quantum phases in materials is to work with pristine materials and devices that have minimal defect concentrations in order to prevent quantum decoherence from scattering and disorder. In this work we construct layered heterostructure devices consisting of a graphene monolayer encapsulated between two atomically smooth layers of hexagonal boron nitride with a bottom graphite gate for tuning the charge carrier density in the monolayer. We then fabricate a coplanar waveguide on top of the device in order to measure the monolayer's high frequency response in the radio to microwave range (10 MHz – 25 GHz). These devices are optimally designed to investigate strongly correlated electronic states at large magnetic fields and millikelvin temperatures. We investigate the competition of Wigner crystal and bubble phases with the fractional quantum Hall states in low Landau levels. Pinning of these states to remnant disorder produces resonances that provide insight into the nature of these states and electron-electron interactions.