Fig. 2: Visualizing Josephson current response to bias current and magnetic field.
a Top sketch shows the measurement sequence that takes the difference between zero and finite current bias. Expected current flow show changing line shapes at various bias current Ibias, with the opposite bias current leading to inverted current flow pattern around the center of the junction. b, c Color map shows z-component of the current-generated magnetic field bz. The arrows show the reconstructed current flow vector. Results are measured using the sequence shown in (a). External magnetic field is Bz = 0.95 mT. The SC electrodes are marked by solid lines and normal metal part is marked by dashed lines. d Phase difference caused by bias current ϕbias extracted from the current flow profile at the junction. The result agrees with the sinusoidal current-phase relation. Inset shows the measured jy(x) at Ibias = Ic, and the fitting results using Supplementary Eqn. 10. The data in the gray area is excluded in the fitting. e Top sketch shows the measurement sequence that takes the difference between symmetric positive and negative Ibias. The expected signals change sign when measuring the 0- and 1-JV states at their respective ∣Ic∣. All signals show cosine-like shape, with amplitude growing with Ibias. f, g bz and current flow vector maps measured using the sequence shown in e). The Josephson current changes sign between 0- and 1-JV states. External magnetic field is Bz = 1.10 mT in (f), and Bz = 1.91 mT in (g). h Effective phase difference across the junction ϕeff = ϕe∣x=W/2 deviates from the external field contribution ϕext (indicated by the shaded area), as a result of induced phase from the Josephson current. Scale bar is 0.5 μm for (b, c, f, g). The measurements are taken at T = 7 K. Error bars in d and h represent standard deviation from fitting.
