Josephson coupling through one-dimensional ballistic channel in semiconductor-superconductor hybrid quantum point contacts

We study a superconducting quantum point contact made of a narrow In${}_{0.75}$Ga${}_{0.25}$As channel with Nb proximity electrodes. The narrow channel is formed in a gate-fitted constriction of InGaAs/InAlAs/InP heterostructure hosting a two-dimensional electron gas. When the channel opening is varied with the gate, the Josephson critical current exhibits a discretized variation that arises from the quantization of the transverse momentum in the channel. The quantization of Josephson critical current persists down to the single-channel regime, providing an unambiguous demonstration of a semiconductor-superconductor hybrid Josephson junction involving only a single ballistic channel.

Figure 1

Schematic drawings of the (a) SQPC and (b) cross section of the wrap-gate QPC. (c) Scanning electron micrograph of a representative device tested. The black scale bar is 300 nm.

Figure 2

I-V characteristics of the SQPC taken at three representative values of $V_{\text{g}}$. The inset shows a magnified view of the I-V curve with $V_{\text{g}}=-2.35$ V.

Figure 3

(a) $V_{\text{g}}$ dependence of $I_{\text{sw}}$. (b) $V_{\text{g}}$ dependence of $dI/dV$ taken at $V=0.2$ mV. For both (a) and (b), the dots represent experimental data, while the lines are fitted curves. Refer to the main text for the details of the fitting. The inset in (b) shows $dI/dV$ taken at $V=2$ mV. Note that the data in the inset were taken in a cooldown cycle different from that in the main panels.

Figure 4

Temperature dependence of the switching current normalized by the value at 0 K. The solid and open circles are experimental data of $I_{sw}$ and $I_r$, respectively. The solid and dashed lines are the curves calculated using the KO-2 model with ${\Delta }_0=0.154$ meV and ${\Delta }_0=1.27$ meV, respectively.