Bias voltage dependence of a flux-sensitive Al/GaAs/Al (SNS) interferometer

We report new results on interferometers based on high transparency superconductor-semiconductor-superconductor junctions composed of Al and highly doped GaAs. The fabricated devices consist of planar dc-SQUID like geometries with an effective flux-sensitive area of about 100-150 /spl mu/m/sup 2/. At zero bias voltage the fabricated interferometers typically exhibit 3% sinusoidal modulation of the conductance as a function of a magnetic field applied perpendicular to the loop. The conductance modulation is caused by resonant Andreev states in the normal GaAs region of the device. With increasing bias voltage of the order of a few microvolts the device is driven out of resonance and the conductance oscillations are extinguished. However, at higher bias voltage corresponding to the superconducting energy gap of Al (178 /spl mu/V) the conductance oscillations reappear but with reduced amplitude.