Fig. 1: Double SQUID device and single-JoFET characteristics.
From: Gate- and flux-tunable sin(2φ) Josephson element with planar-Ge junctions
a Schematic and scanning electron micrograph of the device. A Ge-based SQUID (G-SQUID), embedding JoFETs JN1 and JN2, is connected in parallel to a wider JoFET (JW) used as a reference Josephson junction for current-phase-relation (CPR) measurements. The aluminum arms are modeled by three inductances: L1, L2 and LW. b–d Current-biased measurements of the JoFET characteristics for JW, JN1, and JN2, respectively. In each panel, the measured source-drain voltage is plotted as a function of gate voltage, \({V}_{{{{\rm{G}}}}}^{i}\) (i = W, N1, N2), and source-drain current bias IDC. e (resp. f), Left: critical current, IC, as a function of magnetic flux Φ1 through the large loop in (a). The reference JoFET JW is biased to strong accumulation (\({V}_{{{{\rm{G}}}}}^{W}=-\!1.5\,{{{\rm{V}}}}\)), JN2 (resp. JN1) is pinched off and \({V}_{{{{\rm{G}}}}}^{{{{\rm{N1}}}}}=-\!0.6\,{{{\rm{V}}}}\) (resp. \({V}_{{{{\rm{G}}}}}^{{{{\rm{N2}}}}}=-\!1.5\,{{{\rm{V}}}}\)). The IC oscillations are a direct measurement of JN2 (resp. JN1) CPR. Right: Fast Fourier transform (FFT) of the CPR on the left, calculated over 15 Φ0. Black dashed line: calculated CPR and FFT based on the circuit model in a with parameters obtained from a fit of the data in Fig. 2a.
