Edge effects in microwave measurements of correlated electronic phases in graphene

Strongly correlated electronic phases such as the fractional quantum Hall effect (fQHE) and Wigner crystal (WC) have been studied in 2D electron gases (2DEGs) using DC and AC resistivity measurements. However, the study of WCs using AC measurements have been mostly limited to 2DEGs at the interface of GaAs/AlGaAs heterojunctions. To study WC and fQHE in graphene in the AC regime, we construct devices which incorporate a co-planar waveguide (CPW) coupled to a monolayer graphene (MLG) for microwave transmission spectroscopy studies. There are several design challenges for building devices that have high sensitivity and incorporate pristine MLGs that support these quantum phases. Device designs where MLGs are capacitively coupled to CPWs have low sensitivity. Alternatively, devices where the MLG is resistively coupled to the CPW alleviate the sensitivity issue but introduce frequency-dependent contributions from edges. A third option is creating a gate-defined MLG region that is resistively coupled to the CPW without direct edge contacts. In this talk we will discuss the observation of Landau levels and strongly correlated electronic phases at high magnetic fields and low temperatures using microwave transmission spectroscopy for the various device architecture outlined above.