Fig. 2: Frequency doubling of the G-SQUID CPR.
From: Gate- and flux-tunable sin(2φ) Josephson element with planar-Ge junctions
The G-SQUID is symmetrized by setting \({V}_{{{{\rm{G}}}}}^{{{{\rm{N1}}}}}=-1.5\,{{{\rm{V}}}}\) and \({V}_{{{{\rm{G}}}}}^{{{{\rm{N2}}}}}=-0.6\,{{{\rm{V}}}}\), which equalizes the amplitudes of the first harmonics in JN1 and JN2. JW is kept in strong accumulation (\({V}_{{{{\rm{G}}}}}^{{{{\rm{W}}}}}=-1.5\,{{{\rm{V}}}}\)). a Critical current as a function of the two compensated magnetic fluxes, Φ1 and Φ2, threading the large superconducting loop and the G-SQUID, respectively. b–d G-SQUID CPR (IC vs Φ1) for Φ2 = 0, −Φ0/4, and −Φ0/2, i.e., at the line cuts denoted by green lines in (a). e–g The FFTs obtained from the CPRs in (b–d), respectively, are calculated over 15 Φ0. Black dashed lines in b–g are calculated CPRs (FFTs) based on the circuit model in Fig. 1a with parameters obtained from a fit of the data in a. In d, following a suppression of the odd harmonics (clearly shown in d), we observe the doubling of the CPR frequency as expected for a \(\sin (2\varphi )\) Josephson element.
