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 $Phi_0=h$/2e. Here we report on the fabrication and properties of SQUIDs modulating with a period of $1/2timesPhi_0$. The characteristics of these bicrystal SQUIDs are consistent with either a strong sin(2$phi$) 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.
تحميل البحث