Figure 1

(Color online) (a) Main panel: IVC showing Josephson state at $T=200\mathrm{mK}$. Upper inset: optical image of a device. Lower inset: magnetic field dependence of critical current exhibiting Fraunhofer pattern. (b) Gate dependence of the voltage across a junction in Josephson state for $I=800\mathrm{nA}$. Inset: IV curves as a function of gate voltage. The center area corresponding to the Josephson state is separated from the normal state by the switching current represented by the bright line. (c) Gate dependence of normal state resistance at $T=200\mathrm{mK}$. The superconductivity of the leads was suppressed with a small magnetic field. Inset: mean free path calculated from the transport data. The arrow indicates the onset of the puddle regime. (d) Gate dependence of critical current. Comparison of the data with theoretical predictions for ballistic SGS junction at $T=0$. Green line (dark gray) represents the experimental data; solid black line is the calculated value without fluctuation, and the red (light gray) is the calculated value with fluctuations due to a rf noise temperature of $300\mathrm{mK}$. Inset: zoom into Dirac point.Reuse & Permissions

Figure 2

(Color online) Multiple Andreev reflections. (a) Temperature dependence of the MAR. Curves, taken for different temperatures, are vertically shifted for clarity. The labels show temperatures in units of mK. Dotted lines indicate the first four subgap oscillations. The extra peaks at high bias (seen in the curve just below $T_c$) signal the superconducting to normal transition in the leads. (b) Comparison of normalized subgap features at different doping levels for sample S022207. Inset: normalized differential conductance as a function of $L∕\xi$. Black squares, theoretical values for diffusive junctions from Ref. 25. Triangles, measured values. A similar estimate for the data in Ref. 6 was not possible because the Andreev reflections were absent.Reuse & Permissions

Figure 3

(Color online) Temperature and gate dependence of the Josephson effect. (a) Comparison of the measured temperature dependence of the switching current, $I_c$, with calculated values for ballistic SGS junctions, $I_c^{\mathit{cal}}$. (b) Comparison of measured gate dependence of $V_c=I_c{R}_n$—red curve (gray)—with calculated values from Likharev’s model including corrections for premature switching $V_c^{*}=I_c^{*}{R}_n$ (black curve). The blue curve (dark gray) corresponds to the ballistic model. Inset: ratio of experimental and theoretical values $V_c∕V_c^{*}$, for two of our samples: S032007, S02207, and for data obtained from Ref. 5. The solid line is a guide to the eye.Reuse & Permissions