Overdamped Phase Diffusion in hBN Encapsulated Graphene Josephson Junctions

Hexagonal Boron-Nitride encapsulated Graphene based Josephson junctions (SGS) are in an active stage for studying superconducting phenomena and applications. As such, it is necessary to study how interaction with the environment affects junction behavior. This work characterizes damping behavior by experimentally investigating the phase diffusion mechanism. At non-zero temperature, the SGS can be briefly excited above its superconducting state by thermal noise, the state is quickly recovered, albeit with a net phase shift. The phase shift results in a measurable voltage, even at zero bias current. Josephson junctions can be underdamped or overdamped regime as dictated by the interaction with its environment. Vast majority of previous experimental studies have shown SGS devices to be slightly-to moderately under damped[1]. Here, we conclusively demonstrate overdamped behavior in a SGS, characterized via phase diffusion[2]. Moreover, we present a framework in order to design future underdamped devices. Our results have relevance for SGS-based quantum information devices.

[1] Phys. Rev. Lett. 107, 137005 (2011); Nature Phys. 12, 318 (2015); Phys. Rev. Lett. 117, 237002 (2016).

[2] Phys. Rev. Research 4, 023203 (2022).