Fig. 3: Tuning a superconducting quantum interference device into a symmetric configuration.
From: Charge-4e supercurrent in a two-dimensional InAs-Al superconductor-semiconductor heterostructure
a Differential resistance dV/dI of the superconducting quantum interference device (SQUID) as a function of external flux Φext and current bias I for symmetric junctions. Here, the gate voltage on one junction is VG1 = −0.865 V and the gate voltage on the other junction is VG2 = −0.9 V. In this balanced configuration, there is no diode effect. b Normalized radiation power Pdet,norm. at a detection frequency \({f}_{\det }=7.1\) GHz plotted vs external flux Φext and normalized voltage drop over the SQUID Vint. The map is measured at the same time as in a. At half flux quantum, the 2e radiation signal is suppressed, and the 4e peak becomes the dominant feature. The plots in blue and orange are line cuts in the power map taken at Φext = 0.22 Φ0 and Φext = Φ0/2 respectively, as indicated by the arrows. In c, we bias the SQUID at Φext = Φ0/2, and fix VG2 = −0.875 V. We measure the SQUID differential resistance as a function of current bias and VG1. Moving from left to right, we go from Ic2 > Ic1 to Ic1 > Ic2, crossing a balanced configuration. d Same as in b but for the gate and flux configuration as in c). For specific values of VG1, we see a clear increase in the visibility of the 4e peak. The plots in blue and orange are line cuts in the power map taken at VG1 = −0.89 V and VG1 = −0.8 V, respectively. e Same as in a), but for VG1 = −0.9 V and VG2 = −1 V. In this unbalanced configuration, there is a diode effect. f Same as in b but for the gate configuration as in e. Here, throughout the flux bias range, the 2e peak remains the dominant feature.
