Visualizing supercurrent flow in Josephson Junctions with an atomic sensor

 

Josephson junction has been a subject to a wide field of physics including quantum technology and topological systems due to its phase controllability.[1-3] Although many studies have revealed its flourishing properties, the direct observation of the local state at the junction is still missing to provide intuitive understanding of the physics. The much-utilized conventional measurement with dc transport focusing on the oscillatory critical current [2-4], although effective, is insensitive to features in the zero-resistance state.

In this study, we report high resolution, direct visualization of Josephson vortices in planar junction with normal metal tunneling barrier using nitrogen vacancy centers in diamond. [5] We uncover competing ground states within the zero-resistance regime. The competition rises from phase re-configuration induced by Josephson current and kinetic inductance of thin-film superconductors. [6] We further identify the asymmetry at the junction and explain with a new mechanism for the Josephson diode effect.

 

References:

[1]        M. H. Devoret, et al. Science 339, 1169-1174 (2013)

[2]        M.T. Allen, et al. Nat. Phys. (2015)

[3]        S. Hart, et al. Nat. Phys. (2014)

[4]        Y.-B. Choi, et al. Nat Mat. 19 974  (2015)

[5]        S. Chen, S. Park, et al Arxiv : 2402.02472 (2024)

[6]        J. R. Clem, PRB 81, 144545 (2010)