Fig. 4: Shapiro steps measurements at zero and a half flux quantum for symmetric junctions.
From: Charge-4e supercurrent in a two-dimensional InAs-Al superconductor-semiconductor heterostructure
a On the left, differential resistance dV/dI as a function of drive power Pd and bias current I at constant drive frequency fd = 7.5 GHz and zero external flux Φext = 0 for a gate voltage on the first junction of VG1 = −0.73 V and a gate voltage on the second junction of VG2 = −0.5 V. The drops in differential resistance correspond to the emergence of Shapiro steps. On the right, differential resistance as a function of Pd plotted vs normalized voltage drop Vint over the device. At zero flux, mostly integer Shapiro steps are visible. b Same as in a, but at Φext = Φ0/2. The destructive interference of the first harmonics produces a current-phase relation with double the periodicity of the individual junctions, inducing the emergence of half-integer Shapiro steps.
