Hybrid superconducting circuit architecture to probe van der Waal heterostructures : part 1

Moire and non-moire 2D van der Waals (vdW) systems host a plethora of superconducting states. Yet the nature of the superconducting pairing symmetry, the role played by Coulomb interactions in flat bands, and quantum geometric contributions to the superfluid weight are yet to be fully explored in experiments. Probing these aspects motivates developing new techniques beyond electrical transport. 

Recently, superconducting microwave resonators have been coupled to twisted graphene, yielding insights into the pairing symmetry of its superconducting states. Building on those developments, we develop a hybrid architecture that enables simultaneous quasi-DC electrical transport and microwave impedance measurements of dual-gated vdW heterostructures. In part 1, we outline the design requirements and implementation of our hybrid architecture, to couple a vdW stack to a high-impedance resonator. We demonstrate highly transparent superconducting contacts to graphene using a selective fluorine etch chemistry. We develop on-chip filters to decouple the resonator from loss through quasi-DC probes, thereby enabling us to obtain a high-quality resonance of the hybrid stack-resonator system. In part 2, we show that resonator frequency and quality factor are sensitive probes of the channel resistance as measured independently at quasi-DC frequencies. Our work provides a framework for probing the impedance of vdW systems at microwave frequencies, including kinetic inductance from vdW superconductivity