Half - h/2e - Oscillations of SQUIDs

The current-voltage-voltage characteristics of Superconducting Quantum Interference Devices (SQUIDs) are known to modulate as a function of applied magnetic filed with a period of one flux quantum $\Phi _{0}=h$/2e. Here we report on the fabrication and properties of SQUIDs modulating with a period of 1/2 x $\Phi _{0}$. The characteristics of these bicrystal SQUIDs are consistent with either a strong sin(2\textit{$\phi )$} component of the current-phase relation o f the Josephson current, or with an interaction between the Cooper-pairs, causing an admixture of quartets to the condensate.