A new singularity in the coherent coupling in Al/GaAs/Al SNS junctions at the bias voltage corresponding to the superconducting energy gap

Particularly high transmittivity superconductor-semiconductor barriers formed by MBE growth have been used to form short Josephson planar type Superconductor-Normal-metal-Superconduc tor (SNS) Josephson junctions with lengths down to 1 μm. In these junctions the quasiparticles move diffusively across the normal region and carry along the phase information given to them by Andreev reflections at both SN boundaries. In order to probe the importance of the coherent transport of quasiparticles in the normal region, we formed one of the superconducting electrodes of the junction as an open loop i.e. an SNS1S2 junction. The total transmission probability through this junction which is modulated by the external magnetic flux through the loop, depends on the coherence of the trajectories going across from S to S1 and from S to S2. Oscillations of the conductance in this type of sample versus magnetic field was observed both at VDC=0 and VDC=Δ/e=163 μV. At intermediate as well as higher voltages no oscillations were observed. (orig.)