Half-h/2e critical current - Oscillations of SQUIDs

The current-voltage characteristics of Superconducting Quantum Interference Devices (SQUIDs) are known to modulate as a function of applied magnetic field with a period of one flux quantum Φ0 = h/2e. Here we report on the fabrication and properties of SQUIDs modulating with a fundamental period of 1/2 × Φ0. The characteristics of these bicrystal SQUIDs are consistent with either a strong sin(2ψ) component of the current-phase relation of the Josephson current, or with an interaction between the Cooper pairs, causing an admixture of quartets to the condensate.