Gate Controlled Anomalous Phase Shift in Al/InAs Josephson Junctions*

In a standard Josephson junction the current is zero when the phase difference between superconducting leads is zero. This condition is protected by parity and time-reversal symmetries. However, the combined presence of spin-orbit coupling, and in-plane magnetic field breaks these symmetries, which can lead to a finite supercurrent even when the phase difference is zero. This is the anomalous Josephson effect which can be characterized by the corresponding anomalous phase shift. We report the observation of a tunable anomalous Josephson effect in Al/InAs Josephson junctions measured via a superconducting quantum interference device. By gate controlling the density of InAs, we are able to tune the spin-orbit coupling in the Josephson junction. This gives us the ability to tune the anomalous phase using both in-plane magnetic field and gate voltage. We observe anomalous phase shifts larger than expected from theory for our material parameters. These results open new opportunities for superconducting spintronics, and new possibilities for realizing and characterizing topological superconductivity.