Exploring van der Waals superconductors using a hybrid microwave circuit

The advent of two-dimensional van der Waals materials represents a new frontier in condensed matter physics and quantum device research. However, characterizing these materials remains challenging, as conventional bulk techniques are often inadequate, necessitating the development of specialized approaches. Here, we investigate the superconducting properties of different vdW superconductors by integrating them with a hybrid superconducting microwave resonator. The resonator is significantly modified through its interaction with the flakes, yet they maintain high quality factors. However, we also observe an unexpected upshift of the resonator frequency with increasing temperature, as well as a positive nonlinearity, which obscures the intrinsic signatures of the superconducting gap parameter. Meanwhile, these effects can be modeled as a two-level system (TLS) bath interacting with the resonant mode under specific boundary conditions. Our findings pave the way for realizing high-quality hybrid circuits incorporating van der Waals flakes, enabling the exploration of novel materials and the development of next-generation quantum technologies.