Extended Data Fig. 8: Tunnelling spectroscopy in device 3 (W1 = 120 nm). | Nature

Extended Data Fig. 8: Tunnelling spectroscopy in device 3 (W1 = 120 nm).

From: Evidence of topological superconductivity in planar Josephson junctions

Extended Data Fig. 8

ah, G as a function of Φ and Vsd measured at different values of B|| in device 3 (W1 = 120 nm). In this device, spectroscopy was performed with a QPC forming a tunnel barrier between the top edge of JJ1 and a wide planar Al lead, following the approach of refs 6,7. At B|| = 0, the superconducting probe generates a flux-independent gap \({{\Delta }}_{{\rm{p}}{\rm{r}}{\rm{o}}{\rm{b}}{\rm{e}}}^{\ast }\) ≈ 200 µeV added to the junction gap  ≈ 100 µeV, together with the characteristic features of negative differential conductance, as visible in a. When a moderate parallel field is applied, the superconducting gap below the superconducting plane softens, creating a finite density of states at zero energy. This feature allows the Al plane to be used as an effective normal lead that can probe discrete states close to zero energy in the junction. At B|| = 250 mT, we can see a complete phase modulation of , indicating that the Al plane gap is already soft (see b). As the field is increased, two ABSs move towards zero energy, forming a ZBP first localized at phase bias φ ≈ π and then extending up to φ = 0, as shown in c–f. At higher fields, the induced gap collapses (g, h). The lower value of and critical field compared to that observed in devices 1 and 2 are presumably due to the larger width of the junction.

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