Figure 1: Characterization of SQUID.
From: Evidence for an anomalous current–phase relation in topological insulator Josephson junctions
(a) Scanning electron microscopy (SEM) image of device. The Bi2Se3 flake is outlined with a dashed white line. Top gate is coloured yellow and the niobium leads are coloured blue. Each junction has a length of ∼100 nm and a width of 1 μm. Scale bar, 2 μm. Schematic of device (TI flake and top gate not shown) is shown in inset. Our measurements are sensitive to the sum of the critical currents of two of the junctions, with a phase difference φ2–φ3=2π(Φ)/(Φ0) set by the magnetic flux Φ within the superconducting loop. Here Φ0 is the magnetic flux quantum. The third junction is not directly probed here. It only partially covers the TI flake and thus only weakly modifies the much larger supercurrent circulating around the loop. (b) I–V curves versus temperature at zero magnetic field and top gate bias (B=0 and VTG=0 V), clearly demonstrating zero resistance state. (c) Top gate dependence, showing an abrupt drop in supercurrent. (d) Temperature dependence of critical current for VTG=0 (black squares) and VTG=−18 V (red squares), showing a transformation from ballistic to diffusive behaviour. Note that the supercurrent at low density (VTG=−18 V) is only weakly dependent on temperature up to 800 mK.
