Fig. 2: Superconducting gap tunability.
From: Parity-conserving Cooper-pair transport and ideal superconducting diode in planar germanium
a Sketch of the proximity effect. Al has a superconducting parent gap Δ and it is coupled to the Ge hole gas. The coupling t, and therefore the induced gap Δ*, depends on the thickness of the SiGe tunnel barrier, i.e., on D. b Top-view sketch of the device layout used to perform tunneling spectroscopy. The part of the Ge QW (right side) not covered by Al is tuned to be fully conductive and behaves like a normal metal reservoir. The two split gates are used for creating a tunnel barrier by applying voltages Vdg1 and Vdg2. The accumulation gate which covers the sample without Al on top is not depicted in the sketch. c Side-view sketch of b. The green profile is a sketch of the tunnel barrier for holes formed at the border between the conductive Ge and the hybridized Ge. d [g] dI/dV as a function of V and Vdg = Vdg1 + Vdg2 plotted in logarithmic scale for D8 [D5]. Data for lower Vdg are shown in Fig. S1. e [h] Line-cuts taken from d [g] at different Vdg (see small solid circles) demonstrating a hard gap for sample D5. f [i] Line-cuts taken from d [g] plotted in a normalized scale, in which the measured dI/dV is divided by the normal state conductance GN = (dI/dV)/Gnormal. The traces are shifted vertically by 0.25 GN with respect to each other.
