Anomalously large second Josephson harmonic in quantum well-based junctions

The current-phase relation (CPR) of a Josephson junction (JJ) contains information about the microscopic mechanisms behind supercurrent. The sinusoidal CPR can successfully describe most JJs made with different materials and synthesis technologies. However, CPR can also deviate from simply sinusoidal form, in particular it can feature higher order sinusoidal terms. We investigate InAs quantum well JJs with epitaxial Al contacts. The distance between Al electrodes is of order 100 nm shorter than the mean free path in the quantum well. We perform diffraction pattern measurements, SQUID measurements and Shapiro step measurements all pointing at a strong intrinsic second order harmonic.