Superconducting cavity-based sensing of band gaps in 2D materials

The superconducting coplanar waveguide (SCPW) cavity plays an essential role in various areas like superconducting qubits, parametric amplifiers, radiation detectors, studying magnon-photon, and photon-phonon coupling. Despite its wide-ranging applications, the use of SCPW cavities to study various van der Waals 2D materials is relatively unexplored. In our experiments, we measured the charge compressibility of bilayer graphene using a half-wave SCPW cavity. Our method provides a means to detect subtle changes in the capacitance of the bilayer graphene heterostructure coupled to a half-wave SCPW cavity, which depends on the compressibility of bilayer graphene, manifesting as shifts in the resonant frequency of the cavity. The accuracy of our capacitance measurement is comparable to other state-of-the-art techniques. Our technique can be extended to a broader class of 2D materials, including transition metal dichalcogenides (TMDs) and their moiré where DC transport measurement is often challenging due to high contact resistance.