Probing Kinetic Inductance and Pairing Symmetries in Magic Angle Twisted Bilayer Graphene (Part 1)

The mechanism and pairing symmetry of superconductivity have always been at the forefront of the study of unconventional superconductors. The physics underlying the superconducting phases in magic-angle twisted bilayer graphene (MATBG) may provide revelatory insight beyond the moiré systems, and extend into other strongly-correlated systems such as high-T_C superconductors. Here, we combine DC transport and circuit quantum electrodynamics (cQED) techniques to characterize the kinetic inductance and, consequently the superfluid density, within MATBG samples. The hybrid superconducting circuit grants access to collective behaviors of the superfluid ensemble across the entire MATBG region. In Part 1 of our talk, we will focus on the methodology of this experiment, including the design, simulations, and fabrication of the devices. We present DC and MW characterization to demonstrate gate-dependent microwave resonance that arises from the superconducting phase of MATBG. In part 2, we will present the temperature, DC bias current, and microwave power dependence of the superfluid density in MATBG samples and discuss their implication on the pairing symmetry in MATBG. We stress that the hybrid superconducting circuits demonstrated can be utilized to study other atomically thin 2D superconductors in both DC and AC regimes.